Suggestion on How to Use

Suggestion on How to Use
Industry Trainers are encouraged to use this material in their sessions Download both the PowerPoint file (.ppt) and script file (.pdf) Print the script file (.pdf) and read the script as you view the PowerPoint presentation in the “Slide Show” view. In this way you see the slides in large format and have animation (if there is any) Must have PowerPoint and Adobe Reader application software on your system. Suggestion on How to Use Download both the PowerPoint file (.ppt) and script file (.pdf). Print the script file (.pdf) and read the script as you view the PowerPoint (.ppt) presentation in the “Slide Show” view. In this way you see the slides in large format and have animation (if there is any). Must have PowerPoint and Adobe reader application software on your system.

2005 National Electrical Code® Changes
Affecting Overcurrent Protection

409 New Article 409: Industrial Control Panels
SCCR Marking for Industrial Control Panels SCCR Marking on Motor Controllers 670.3(A) Industrial Machinery SCCR Marking 440.4(B) HVAC Short Circuit Current Rating (SCCR) Marking 230.82(3) SCCR Marking on Meter Disconnects Definition for Coordination (selective) Selective Coordination: Emergency Systems Selective Coordination: Legally Required Standby Sys. Selective Coordination: Healthcare Essential Circuits 240.86(A) Existing Facilities: Series Rating Engineering Method Definition for Supplementary OCPD 240.5(B) Appliance and Extension Cord Protection 240.60(D) Renewable Fuses: Replacement ONLY 410.73(G) Disconnecting Means: Electric Discharge Lighting 430.52(C)(6) Self Protected Comb. Ctrl 1 Pole Interrupting Capacity 430.83(E) Motor Controllers Slash Voltage Requirement Summary of code changes for 2005 covered in this presentation

Summary of Changes Requiring Marked Short Circuit Current Rating
New Article 409 Industrial Control Panels Marked on Industrial Control Panels Marked on Motor Controllers 440.4(B) Marked on HVAC Greater than 60A Non Residential Marked on Industrial Machinery 230.83(3) Marked on Meter Disconnect Switches Several sections of the 2005 NEC were added or revised to require components or equipment electrical panels to be marked with their short circuit current rating. Article 409 Industrial Control Panels is an entirely new article.

Industrial Control Panels
Example of industrial control panel – new Article 409 for Industrial Control Panels is an important addition.

2002 NEC® and Before Required marking for interrupting rating of main Overcurrent Protective Device on Industrial machinery (670.3) Industrial control panels, HVAC control panels, motor controllers, and meter disconnects were not required to be marked with SCCR Prior to the 2005 NEC it was required to mark industrial machinery electrical panels with the interrupting rating of the main overcurrent protective device where one was installed in the panel. However, this was did not ensure the electrical panel was adequately protected against short circuits as required per The other components and industrial control panels were not required to be marked with their short-circuit current ratings.

Now NEC ® Required to be marked with short circuit current rating: Components Motor Controllers Meter Disconnects Assembly Industrial Control Panels Industrial Machinery Electrical Panels HVAC Panels above 60A non-residential Prior to the 2005 NEC it was required to mark industrial machinery electrical panels with the interrupting rating of the main overcurrent protective device where one was installed in the panel. However, this was did not ensure the electrical panel was adequately protected against short circuits as required per The other components and industrial control panels were not required to be marked with their short-circuit current ratings.

WHY???? Short circuit currents can cause extensive damage to components and industrial control panels. This can be a cause of fire or safety hazards for buildings and personnel.

Short Circuit Current Ratings (SCCR)
What is a Short Circuit Current Rating? The maximum short circuit current a component, assembly or equipment can safely withstand when protected by a specific overcurrent protective device, or for a specified time interval SCCR pertains to protection of components, multiple component assemblies or entire control panels This slide states the meaning of a short circuit current rating and to what a SCCR pertains. It is important to understand that short circuit current ratings are different than interrupting ratings, which are discussed on the next slide.

Short Circuit Current Ratings
Short Circuit Current Rating is not the same as Interrupting Rating: Interrupting Rating – Maximum available current a fuse or circuit breaker can safely interrupt under standard test conditions Interrupting Rating only pertains to the overcurrent protective device Class H Fuses 10kAIR Adequate Interrupting Ratings do not ensure protection of circuit components, assemblies or equipment Many people confuse short circuit current ratings with interrupting ratings. An interrupting rating is only applied to an overcurrent protective device, such as a fuse or circuit breaker. Components and equipment which are not intended to interrupt fault currents are rated with short circuit current ratings. It is certainly important to ensure that overcurrent protective devices have an adequate interrupting rating for the available short circuit current – in fact, it is required in – however, this alone does not ensure protection of circuit components. One must compare the short circuit current ratings of the circuit components against the available short circuit current, or in some cases, the current let-through of the next upstream overcurrent device. 50,000A Fault Inadequate Interrupting Rating

Marked Short Circuit Current Ratings
Why are Marked Short Circuit Current Ratings Important? Needed to ensure compliance with NEC® Helps to eliminate hazards where components and equipment are applied above their ratings Simplifies inspection approval process Any device that is applied outside of its ratings – whether it is the voltage rating, short circuit current rating, etc. – poses a fire and safety hazard to surrounding space and personnel. Marked short circuit current ratings are needed to ensure compliance with , to help eliminate components and equipment being applied beyond their rating, and to simplify the inspection approval process.

Component Marking Requirements Short Circuit Current Rating may be established during testing as part of the listing and labeling process for individual components or multiple component assemblies A component in this context is an individual controller, contactor, etc. In contrast later, equipment such as industrial control panels are discussed. Components have a short circuit current rating that is established as part of the listing and labeling process with third-party testing agencies, such as UL and CSA. These components are typically part of large production runs, making short circuit testing feasible.

Meter Disconnects Marked Short Circuit Current Rating
230.82(3) – Equipment Connected to the Supply Side of Service Disconnect. Only the following equipment shall be permitted to be connected to the supply side of the service disconnecting means: (3) Meter disconnect switches nominally rated not in excess of 600 volts that have a short-circuit current rating equal to or greater than the available short circuit current, provided all metal housings and service enclosures are grounded. Here is the applicable text from the 2005 NEC®. The next slide summarizes the key points.

230.82(3) Meter Disconnects Marked Short Circuit Current Ratings
Meter Disconnect Switches: Must have a marked short circuit current rating equal to or greater than the available short circuit currents Typically achieved by a fused disconnect utilizing current-limiting fuses Disconnects are allowed to be installed ahead of the service disconnect when they are used to isolate watthour meters for installation and removal. These switches allow utilities to install and maintain meters in an electrically safe working environment. However, being installed on the supply side of the service disconnect, these switches can be subjected to extremely high fault currents. Applying these disconnects without considering their short circuit current rating could pose a real danger to personnel. The solution typically will be a fused disconnect with current-limiting fuses that is able to achieve a high marked short-circuit current rating.

430.8 Motor Controllers Marked Short Circuit Current Ratings
A controller shall be marked with the manufacturer’s name or identification, the voltage, the current or horsepower rating, the short-circuit current rating, and such other necessary data to properly indicate the applications for which it is suitable. A motor controller is any device that is meant to control the on/off function of a motor circuit. They are not usually appropriate for isolating the circuit from the supply, but some can be used as disconnects in certain conditions. 430.8 requires motor controllers to be marked with their short-circuit rating. There are product standard procedures for determining motor controller short circuit current ratings. These are mentioned in the slide after the next slide.

430.8 Motor Controllers Marked Short Circuit Current Ratings
Exceptions where the Short Circuit Current Rating is not required on the controller: 1/8HP or less motors which are normally left running and constructed not to be damaged by overloads 1/3HP or less portable motors where the controller is the attachment plug and receptacle The rating is marked elsewhere on an assembly The assembly into which the controller is to be installed is marked with a rating Controller is rated 2HP or less at 300V or less and is listed exclusively for general purpose branch circuits Exceptions to motor controllers being marked with short-circuit current rating

Motor Controllers Marked Short Circuit Current Ratings
UL 508 has: “Standard” fault current test An optional “high available” fault current test Optional Type 2 “no damage”, “high available” fault current (UL 508E) “Standard” level: 5kA for HP ratings 10kA for HP ratings, etc. Current limiting fuses are often used in the optional “high-available” fault current tests and Type 2 “no damage” tests to achieve high short circuit current ratings UL 508 is the product standard for industrial control components has test procedures to establish the short-circuit current rating for these products. There is a standard fault current test level and an optional high available fault current test level. In either of these two test procedures extensive damage is permissible. UL 508E has an Outline for Investigation to establish a high fault current rating short circuit current with “no permanent damage” to the controller. Current limiting fuses are often used to achieve the optional high fault current short-circuit current rating and Type 2 “no damage” short-circuit current rating.

Motor Controller Label Example (from an 80A, 40HP rated controller) GENERAL PURPOSE SWITCH INTERRUPTEUR, USAGE GENERAL Short circuit rating 100kA at 600VAC max when protected by 100A class J or T 5kA when protected by 150A class H or RK5 fuses LISTED 3E73 MAN MTR CNTRL Notice the higher short circuit current rating with the more current-limiting J and T class fuses. Notice also that the “standard” rating is achieved with H or RK5 class fuses. The short circuit current rating is not typically achieved without an overcurrent protective device.

Equipment Marking Requirements Short Circuit Current Rating can be established during testing as part of the Listing and Labeling process Where testing is not feasible, Short Circuit Current Ratings can be determined using approved engineering methods Equipment, like components, can have short circuit current ratings that are determined as part of the listing and labeling of the equipment. However, short circuit current testing is not always a practical option. For example, many industrial control panel builders often build unique panels to fulfill a specific need for a client. In these cases it is too costly and time consuming to build several examples of the panel for short-circuit testing purposes.

– Industrial Control Panels – Marking. An industrial control panel shall be marked with the following information that is plainly visible after installation: (3) Short-circuit current rating of the industrial control panel based on one of the following: a. Short-circuit current rating of a listed and labeled assembly b. Short-circuit current rating established utilizing an approved method FPN: UL 508A-2001, Supplement SB, is an example of an approved method requires industrial control panels to be marked with their short circuit current rating. This is very important. It makes it much easier for the designer, contractor and inspector to ensure the industrial control panel has a short circuit current rating equal to or greater than the available short circuit current at the point of panel installation. The short circuit current rating of industrial control panels and electric panels for industrial machinery can be established with testing as part of the listing and labeling of the device to a product standard. Where this is not feasible, such as one-off panels, an approved engineering method can be used. UL 508A Supplement SB has a method for determining the short circuit current ratings for each branch circuit in an industrial control panel. The short circuit current rating of each branch are then compared against the peak current let-through of the feeder current limiting overcurrent protective device. If the peak let-through of the feeder overcurrent protective device is less than or equal to the lowest branch circuit short circuit current rating, the panel can be marked with that level as the short circuit current rating. Since fuses have umbrella limits with UL, it is very simple to use the current limitation of fuses.

Industrial Control Panels: Now Marked with Short Circuit Current Rating

670.3 – Industrial Machine Nameplate Data. (A) Permanent Nameplate. … shall be attached to the control equipment enclosure or machine and shall be plainly visible after installation. The nameplate shall include the following information: (4) Short-circuit current rating of the industrial control panel based on one of the following: a. Short-circuit current rating of a listed and labeled assembly b. Short-circuit current rating established utilizing an approved method FPN: UL 508A-2001, Supplement SB, is an example of an approved method 670.3 requires control panels for industrial machinery to be marked with their short circuit current rating. These are treated in the same manner as industrial control panels.

Example: Industrial Machinery Control Panel Label Plastics Processing Machine Serial Number Voltage Current SN2356YUP77 volts 87 Amperes Largest Motor H.P. 25 Horsepower Diagram Numbers CM 12.1 THRU CM 12.5 Phase & Freq.. 3ph., 60 Hz Quality Machine Tool Somewhere, USA Short Circuit Current Rating 100,000 Amperes RMS Max OCP Device 60 Ampere Short Circuit Current Rating 100,000 Amperes RMS Example label properly marked with short circuit current rating

440.4(B) – Marking on Hermetic Refrigerant Motor-Compressors and Equipment (B) Multimotor and Combination-Load Equipment. Multimotor and combination-load equipment shall be provided with a visible nameplate marked with the maker’s name, the rating in volts, frequency and number of phases, minimum supply circuit conductor ampacity, the maximum rating of the branch-circuit short-circuit and ground-fault protective device, and the short-circuit current rating of the motor controllers or industrial control panel. 440.4(B) SCCR marking requirement for HVAC equipment

Combination Load and Multimotor HVAC and Refrigeration Equipment Exceptions: Equipment used in one and two family dwellings Cord-and-attachment-plug connected equipment Equipment supplied by a branch circuit protected at 60A or less Shows the exceptions to requiring HVAC equipment to be marked with SCCR. Essentially, only commercial and industrial combination load and multimotor equipment will be required to marked short circuit current ratings.

Example of HVAC Label HVAC Control Panel Serial Number HVDB Current 72 Amperes Min Circuit Ampacity 90 Amperes Max Fuse Size 125 Ampere Voltage volts Phase & Freq.. 3ph., 60 Hz Short Circuit Current Rating 40,000 Amperes RMS Short Circuit Current Rating 40,000 Amperes RMS Example HVAC label HVAC Equipment, Inc. Anytown, USA

Ensuring Compliance For equipment requiring Marked Short Circuit Current Ratings Engineer provides: Available short circuit currents at each installation point Short circuit current rating of each piece of equipment or panel During site inspection, inspector compares actual marked short circuit current ratings to the submitted data: planned SCCRs and available short circuit currents Ensuring Compliance For the affected types of equipment, simply require the following: 1. For the plan review process, the engineer supplies the available short-circuit current at each equipment installation point and the specific short-circuit current rating for each piece of equipment or industrial control panel. 2. Upon site inspection, compare the actual equipment marked short-circuit current rating to the submitted data to ensure the rating is indeed as specified and sufficient for the available short-circuit current available at the point of installation.

Ensuring Compliance This method requires proper engineering and analysis by the design engineers and proper review by inspectors.

Ensuring Compliance: Simple Check For Short Circuit Current Rating
500 KVA 480/277V 1 5 % Z 13,222 A 1500 KVA 2 2 % Z 99,165 A Determine the maximum, worst case short circuit current available at the terminals of the supply transformer Verify that all required equipment is marked with a short circuit current rating sufficient for this maximum, worst case available current If SCCRs are sufficient: installation approved. If this SCCRs insufficient by this quick check method, a detailed analysis may be required A simple method if all the equipment has high short-circuit current ratings: 1. Verify the maximum, worst case short-circuit current available at the terminals of the supply transformer. 2. If all the equipment in the system has short-circuit current ratings greater than this maximum, worst case available short-circuit current, then the detailed short-circuit current study is not necessary. Equipment properly protected by current-limiting fuses can easily achieve short-circuit current ratings of 100,000A or 200,000A. If some of the equipment in the system does not have sufficient short circuit current ratings for this simple check method, then a short-circuit study to the equipment installation point is necessary. Cooper Bussmann® has several tools for calculating available short-circuit currents. At there are: Software program: simple one point at a time short circuit calculator that can be downloaded In the SPD protection handbook publication there is the Point to Point short circuit calculation method The EPR-1 Electrical Plan Review publication has the Point to Point short circuit current method and calculations for an example system.

Achieving High Short Circuit Current Ratings
High Short Circuit Current Ratings Make Equipment and Controllers: Easier to specify and install for compliance More flexible – can be moved from location to location safely Components or control panels that achieve high short circuit current ratings are more desirable. With high short circuit current ratings much less analysis needs to be done by the designer. Also, industrial control panels and industrial machinery typically are moved periodically as manufacturers move their production lines, etc. A high short circuit current rating on equipment, is a benefit allowing the owner more flexibility in moving the equipment.

Achieving High Short Circuit Current Ratings
Current Limiting Fuses: Reduce fault energy Can be used to achieve high short circuit current ratings for motor controllers, assemblies of multiple components, disconnects, and industrial control panels FUSETRON® dual-element, time delay fuses FRS-R and FRN-R (Class RK5) provide current- limiting protection. The level of current limiting ability is good. A better choice for applications using Class R fuse clips is the LOW-PEAK® LPS-RK_SP & LPN-RK_SP (Class RK1) because these fuses are more current-limiting and enter their current-limiting range at lower fault levels. LOW-PEAK® fuses, LPJ_SP (Class J), LPS-RK_SP & LPN-RK_SP (Class RK1), LP-CC (Class CC) and KRP-C_SP (Class L) and TRON JJN/JJS fuses (Class T), offer the best practical current-limiting protection. They have a significantly better degree of current limitation than the other alternatives discussed. In addition, they typically enter their current-limiting range at lower currents than the other fuses or limiter alternatives. The LOW-PEAK® family of fuses is the most current-limiting type fuse family for general protection and motor circuit protection.

Regulatory - 2005 NEC® Changes Marked Short Circuit Current Ratings
Before Now Marked 200 kA SCCR Plastics Processing Voltage Current volts 87 Amperes Phase & Freq.. 3ph., 60 Hz XYZ Machine Company Anywhere, USA Current Rating Short Circuit Current Rating 200 kA 400A Class J Fuse Disconnect Listed 200,000A SCCR Fuses and Power Distribution Block Listed 200,000A SCCR Protected by 400A Class J Fuses Disc PDB This is a simple example of how current limiting fuses can be used to achieve high short circuit current ratings for industrial control panels. There are other methods but this is a sure method. In this case, the motor branch circuit components are tested and listed to UL 508 with 200,000A short circuit current rating when protected by specific type and ampere rating current limiting fuses. The power distribution block is tested and listed with a 200,000A short circuit current rating when protected by Class J 400A fuses. The 400A Class J fused disconnect is tested and listed with a short circuit current rating of 200,000A. This entire panel then can be listed and marked with a 200,000A short circuit current rating. Branch circuits with current limiting fuses, contactors and overloads Listed 200,000A SCCR

Summary: The 2005 NEC® now requires short circuit current ratings to be marked on: Meter Disconnect Switches Motor Controllers Industrial Control Panels Industrial Control Panels for Industrial Machinery Combination Load and Multimotor HVAC and Refrigeration Equipment Summary

Summary of Changes Selective Coordination of Overcurrent Protective Devices
Definition: Coordination Selective Required for Emergency Systems Required for Legally Required Standby Systems Required for Essential Electrical Standby Systems Several sections of the 2005 NEC were added to require selective coordination for fuses or circuit breakers on specific systems.

Selective Coordination
2005 NEC® New Article 100 Definition Coordination (Selective) Localization of an overcurrent condition to restrict outages to the circuit or equipment affected, accomplished by the choice of overcurrent protective devices and their ratings or settings. The 2005 NEC added a definition for selective coordination in Article 100.

What is Selective Coordination?
Isolates an overloaded or faulted circuit Only the nearest upstream overcurrent protective device opens Why is it required? Vital for critical systems Increase system reliability Selective coordination is now required for increased system reliability, which is vital for these critical systems. Selective coordination can be defined as isolating an overloaded or faulted circuit from the remainder of the electrical system by having only the nearest upstream overcurrent protective device open. OPENS Fault NOT AFFECTED

Selective Coordination: Avoids Blackouts
Lacking Selective Coordination With Selective Coordination Fault Fault Selective Coordination is the ability of a system to isolate an overcurrent. Without selective coordination, many or all of the upstream devices can also open causing unnecessary power losses to other non-faulted or non-overloaded loads. With selective coordination, the device closest to the overcurrent is the only device which opens, unnecessary power loss is avoided. The concept is easy to understand. Most people just assume that selective coordination is achieved if the upstream overcurrent protective devices have larger ampere ratings. You will discover that this is not the case. In the examples shown, the fault is on a branch circuit. Faults can occur on feeders too. The feeder overcurrent protective devices need to be selectively coordinated with the main overcurrent protective devices. UNNECESSARY POWER LOSS NOT AFFECTED OPENS

Selective Coordination Requirements
Articles affected 700 Emergency Systems 701 Legally Required Standby Systems 517 Health Care Facilities Selective coordination is an important new NEC® 2005 requirement that is consistent with the critical need to keep these loads powered even with the loss of normal power. Article 700, Emergency Systems, and Article 701, Legally Required Standby Systems have several requirements that are based upon providing a system with reliable operation, reduction in the probability of faults and minimizing the effects of an outage to the smallest portion of the system as possible. Article 517, Health Care Facilities, requires essential electrical systems to meet the requirements of Article 700 except as amended in Article 517.

Other supporting requirements 700.4 Maintenance and Testing Requirements 700.9(B) Emergency circuits separated from normal supply circuits 700.9(C) Wiring specifically located to minimize system hazards Failure of one component must not result in a condition where a means of egress will be in total darkness The objective of these requirements is to ensure system uptime with the goal of safety of human life during emergencies or for essential health care functions. Selective coordination of overcurrent devices fits well with the other requirements such as: 700.4 maintenance and testing requirements 700.9(B) emergency circuits separated from normal supply circuits 700.9(C) wiring specifically located to minimize system hazards failure of one component must not result in a condition where a means of egress will be in total darkness

Emergency system(s) overcurrent devices shall be selectively coordinated with all supply side overcurrent protective devices. Blackout New NEC® 2005 requirement For emergency circuits, selective coordination required through the normal power source and the emergency power source.

Emergency Systems Required in places of assembly or where panic control is needed Hotels, theaters, sports arenas, health care facilities and similar institutions Provide power for: Ventilation, fire detection, alarm systems, elevators, fire pumps, public safety communications, and continuous processes Emergency systems are considered in places of assembly where artificial illumination is required and for areas where panic control is needed such as hotels, theaters, sports arenas, health care facilities, and similar institutions. Emergency systems also provide power to functions for ventilation, fire detection and alarm systems, elevators, fire pumps, public safety communications, or industrial processes where interruption could cause severe human safety hazards.

Legally required standby system(s) overcurrent devices shall be selectively coordinated with all supply side overcurrent protective devices. New NEC® 2005 requirement Selective coordination is required for the path through the normal power supply and the legally required standby source of power.

Legally Required Standby Systems
Supply power to selected loads when normal source fails Serve loads to: Heating and refrigeration, communications, ventilation and smoke removal, sewage disposal, lighting systems, and continuous processes Legally required standby systems are intended to supply power to selected loads in the event of failure of the normal source. Legally required standby systems typically serve loads in heating and refrigeration, communication systems, ventilation and smoke removal systems, sewage disposal, lighting systems, and industrial processes where interruption could cause severe human safety hazards.

Application of Other Articles. The essential electrical system shall meet the requirements of Article 700, except as amended by Article 517. Article 517 covers health care facilities Selective coordination required in essential electrical systems – There are no amendments in Article 517 concerning selective coordination of overcurrent protective devices New NEC® 2005 requirement Article 517 cover health care facilities Notes: 1. Article 517 has no amendment to the selective coordination requirement, therefore selective coordination is required. 2. Selective coordination is required for both the normal supply path and the emergency system path.

Essential Electrical Systems
In health care facilities Designed to ensure service to lighting and power in critical areas Essential systems include: Critical branch, life safety branch, and equipment systems essential for life safety Essential electrical systems in healthcare facilities are portions of the electrical system designed to ensure continuity of lighting and power to designated areas/functions during normal source power disruptions or disruptions within the internal wiring system. Essential electrical systems can include the critical branch, life safety branch, and equipment systems which are essential for life safety and orderly cessation of procedures during normal power disruptions.

Objectives For These Important Circuits
Keep loads powered in the event of loss of normal power Ensure system uptime Ensure safety to human life in an emergency Reduce the probability of faults Provide reliable operation Minimize the effects of an outage Selective coordination requirements fit well with these objectives Selective coordination is an important new NEC® 2005 requirement that is consistent with the critical need to keep these loads powered even with the loss of normal power. Article 700, Emergency Systems, and Article 701, Legally Required Standby Systems have several requirements that are based upon providing a system with reliable operation, reduction in the probability of faults and minimizing the effects of an outage to the smallest portion of the system as possible. Article 517, Health Care Facilities, requires essential electrical systems to meet the requirements of Article 700 except as amended in Article The objective of these requirements is to ensure system uptime with the goal of safety of human life during emergencies or for essential health care functions. Selective coordination of overcurrent devices fits well with the other requirements such as: 700.4 maintenance and testing requirements 700.9(B) emergency circuits separated from normal supply circuits 700.9(C) wiring specifically located to minimize system hazards failure of one component must not result in a condition where a means of egress will be in total darkness

Selective Coordination: Normal Supply
Emergency Source Normal Source N E ATS Typical one-line circuit diagram with emergency circuit.

Unnecessary Feeder Outage
Selective Coordination: Normal Supply Emergency Source Normal Source Unnecessary Feeder Outage N E ATS Opens Not Affected Unnecessary Power Loss Normal power If overcurrent protective devices in the emergency system are not selectively coordinated, a fault at X1 on the branch circuit may unnecessarily open the sub-feeder; or even worse the feeder or possibly even the main. In this case, emergency circuits are unnecessarily blacked out. With selective coordination as a requirement for emergency, legally required standby, and essential electrical systems, when a fault occurs at X1 only the nearest upstream fuse or circuit breaker supplying just that circuit would open. Other emergency loads would remain powered. This shows a fault on an emergency branch circuit when the power is from the normal power source. In this case the overcurrent protective devices are not selective coordinated and the feeder OCPD also opens. This unnecessarily blacksout the other branch circuits fed by that feeder. This is no longer permitted. Fault X1

Unnecessary Main Outage
Selective Coordination: Normal Supply Without Emergency Source Normal Source Unnecessary Main Outage Blackouts Possible! N E ATS Opens Not Affected Unnecessary Power Loss Normal power This shows the fault on the branch unnecessarily opening the feeders and main on the normal power source. In this case, emergency circuits are unnecessarily blacked out. This system does not comply with the selective coordination requirements for emergency, legally required standby, and essential electrical systems. Fault X1

Blackouts Possible! Selective Coordination: Normal Supply Without With
Emergency Source Emergency Source Normal Source Normal Source Blackouts Possible! N E ATS N E ATS Opens Not Affected Unnecessary Power Loss Normal power This diagram on the right will illustrate the benefits of selective coordination when the emergency branch circuit is connected to the normal power source. Fault X1

Blackouts Prevented! Blackouts Possible!
Selective Coordination: Normal Supply Without With Emergency Source Emergency Source Normal Source Normal Source Blackouts Prevented! Blackouts Possible! N E ATS N E ATS Isolated to Branch Only Opens Not Affected Unnecessary Power Loss Normal power This illustrates the benefits of selective coordination when the emergency branch circuit is connected to the normal power source. A fault on the emergency branch circuit is opened only by the branch circuit overcurrent protective device and no other upstream devices open. Therefore, all the others loads remain powered by the normal power source. With selective coordination as a requirement for emergency, legally required standby, and essential electrical systems, when a fault occurs at X1 only the nearest upstream fuse or circuit breaker supplying just that circuit would open. Other emergency loads would remain powered. Fault X1 Fault X1

Selective Coordination: Emergency Supply
Source Normal Source N E ATS Emergency Power Now the power is from the emergency source.

Unnecessary Feeder Outage
Selective Coordination: Emergency Supply Emergency Source Normal Source Unnecessary Feeder Outage N E ATS Opens Not Affected Unnecessary Power Loss Emergency Power If overcurrent protective devices in the emergency system are not selectively coordinated, a fault at X1 on the branch circuit may unnecessarily open the sub-feeder. In this case, emergency circuits fed by the sub-feeder are unnecessarily blacked out. Fault X1

Unnecessary Outage Entire
Selective Coordination: Emergency Supply Without Emergency Source Normal Source Unnecessary Outage Entire Emergency Source Blackouts Possible! N E ATS Opens Not Affected Unnecessary Power Loss Emergency Power If the overcurrent protective devices are not selectively coordinated, it is even possible for the fault current to unnecessarily open the feeders and main of the emergency source path. This could shut down all power to the emergency loads unnecessarily. Fault X1

Blackouts Possible! Selective Coordination: Emergency Supply Without
Source Emergency Source Normal Source Normal Source Blackouts Possible! N E ATS N E ATS Opens Not Affected Unnecessary Power Loss Emergency Power The diagram on the right will illustrate the benefit of overcurrent protective devices that have been chosen that are selectively coordinated for the emergency path. Fault X1

Blackouts Prevented! Blackouts Possible!
Selective Coordination: Emergency Supply Without With Emergency Source Emergency Source Normal Source Normal Source Blackouts Prevented! Blackouts Possible! N E ATS N E ATS Isolated to Branch Only Opens Not Affected Unnecessary Power Loss Emergency Power In this case, for all overcurrents, only the nearest upstream overcurrent protective device will open if there is a downstream overcurrent. In this case, a fault on the branch circuit is cleared without the sub-feeder, feeder or main of the emergency power source opening. With selective coordination as a requirement for emergency, legally required standby, and essential electrical systems, when a fault occurs at X1 only the nearest upstream fuse or circuit breaker supplying just that circuit may open. Other emergency loads would remain powered. Fault X1 Fault X1

Selective Coordination Ensuring Compliance
Requires proper engineering, specification and installation Designer must provide proper documentation of coordination Site inspection should verify correct devices are installed per plans to achieve coordination Achieving the proper overcurrent protective device selective coordination requires proper engineering, specification and installation of the required devices. During the plan review process, it is the design engineer’s responsibility to provide documentation that verifies the overcurrent devices are selectively coordinated for the full range of overcurrents that can occur in the system. And the site inspection should verify the overcurrent protective devices are installed as specified to achieve selective coordination.

What must to be considered?
So now the concept of selective coordination is understood and the 2005 NEC requirements for selective coordination are understood. How can a system be designed and installed to ensure the overcurrent protective devices are selectively coordinated? It is possible for both fusible and circuit breaker systems to be selectively coordinated with proper analysis and selection. However, proper analysis must be done by a qualified person.

Selective Coordination - Fuses
Tm Ta Tc MELTING ENERGY Short Circuit Region Selectivity Ratio Guide (based on I2T) LINE SIDE LOAD SIDE KRP-C-1200SP LPS-RK-600SP AVAILABLE SHORT-CIRCUIT CURRENT Tc Loadside fuse must clear prior to lineside fuse melting Modern current limiting fuses are typically easy to selectively coordinate. For a branch circuit fuse to be selectively coordinated with a feeder fuse (or feeder fuse to a main fuse), it is necessary that the branch circuit fuse clear before the feeder fuse melts. It is that simple. This diagram illustrates this point. The clearing energy of the downstream fuses has to be less the energy required to melt the fuse link of the upstream fuse. With fuses, this is predictable based on the fuse manufacturer, type fuses and fuse ampere ratings. The black dotted lines represent the fault current that would flow if the fuses were not in the circuit. In the lower curve, the downstream fuse (600A fuse), melts and clears as depicted by the small red triangle. There is a thermal energy associated with this let-through current by the 600A fuse. The upper diagram represents how the 1200A fuse would respond to this fault if the 600A fuse were not in the circuit below. The larger red triangle represents the current that flows to melt the 1200A fuse. The white triangle to the right bounded by the red line on the right is the clearing portion of the 1200A fuse. When the 600A fuse is in the circuit being feed by the 1200A fuse, the 600A fuse must clear the small red triangle in the lower diagram before the 1200A fuse melts (the thermal energy associated with the red triangle in the upper diagram. Fuse manufacturers have run tests and published Selective Coordination Ratio Tables to make this an easy, simple design decision. See the next two slides. CLEARING ENERGY

Selective Coordination
Fuses Published selectivity ratios Short circuit study unnecessary Selective coordination is easy with Bussmann® fuses by using the published fuse selective coordination ratios; a full short-circuit and coordination study is not necessary to verify selective coordination. See example on the following slide.

Selective Coordination - Fuses
Circuit Selectively Coordinated Loadside Fuse KRP-C_SP LPJ_SP LPS-RK_SP 2:1 - KRP-C_SP LPJ_SP LPS-RK_SP 2:1 - KRP-C_SP LPJ_SP LPS-RK_SP 2:1 - Low Peak KRP-C-800SP Lineside Fuse Low Peak LPJ-100SP Low Peak LPS-RK-20SP 800/100 = 8:1 only 2:1 needed Selective Coordination achieved This is an example of how easy it is to selectively coordinate a fusible system. Each fuse type and ampere rating must be compared with the fuse upstream. By using the published ratios, it is simple to verify if selective coordination is achieved. In this example the branch circuit fuse is selectively coordinated with the feeder fuse and the feeder is selectively coordinated with the main fuse. Therefore the entire circuit is selectively coordinated. If a fault occurs on the branch circuit only the branch circuit fuse will open. If the fault occurs on the feeder circuit, only the feeder fuse will open. Overloads or faults of any level up to 300,000A 100/20= 5:1 only 2:1 needed Selective Coordination achieved

Selective Coordination – Circuit Breakers
Depends on characteristics and settings Difficult to achieve May be higher cost Full short circuit study is necessary Proper analysis and interpretation a must Selective coordination with circuit breakers depends on their characteristics and settings as well as the circuit parameters for the specific application. It is generally difficult to achieve selective coordination with common thermal magnetic circuit breakers that incorporate instantaneous trip settings. Typically circuit breakers with short-time delay settings or zone selective interlock features may be necessary, which can add to the cost and may create other system issues. If circuit breakers are to be considered, a full short-circuit current and coordination study must be completed with proper analysis and interpretation. See circuit breaker examples on the following slides.

90A & 400A Molded Case Circuit Breakers Inherent long delay between unlatching and interrupting due to mechanical means of breaking current Upstream breaker can unlatch before the downstream breaker can clear the fault Lack of Selective Coordination in the Short-Circuit Region Here is an example that illustrates the analysis for circuit breakers with instantaneous trip settings. It is very difficult and in most cases impossible to design selective coordination for a system with all the circuit breakers having instantaneous trip settings.

Not Coordinated above 900A 800 A. CB 0.1 Seconds 100 A. CB IT Non Adjustable 20 A. CB IT Non Adjustable In this case the main and feeder circuit breakers are coordinated since the main is equipped with a short time delay setting and it has no instantaneous trip setting. The branch circuit breaker coordinates with the feeder circuit breaker as long as the fault current on the branch circuit is no greater than 900A. If the short circuit study confirms that the maximum short circuit current at the branch is no greater than 900A then this system is coordinated. Coordinated for overloads and faults less than 900A 900A

Selectively Coordinated up to CBs’ Interrupting Ratings 800 A. CB 0.4 Seconds 100 A. CB 0.1 Seconds 20 A. CB IT Non Adjustable This illustrates selective coordination for a circuit breaker system. The branch circuit breaker has an instantaneous trip and the feeder and main circuit breakers have short time delay settings that do not cross over. This can be achieved using low voltage power circuit breakers (which can add significant cost.) If circuit breakers are not maintained, extended clearing times or nuisance operation may compromise coordination. The Cooper Bussmann SPD Selecting Protective Devices publication (download from has an in-depth discussion on selective coordination analysis with the published fuse selectivity ratios, some simple evaluation rules for coordination of instantaneous trip circuit breakers, and illustration of short-time delay circuit breakers. Overcurrents of any level up to CBs’ Interrupting Ratings

Summary of Changes Selective Coordination Required
100 Definition 700 Emergency Systems 701 Legally Required Standby Systems 517 Health Care Facilities: Essential Electrical Systems

Summary of Changes Series Ratings for Existing Systems
240.86(A) Series Ratings

Series Ratings The 2005 NEC®, section (A), will now permit selection of series rated combinations for existing systems when the selection is made by a licensed professional engineer. The 2005 NEC has added a new (A) which concerns applying series rating combinations for existing systems.

Series Ratings First … What is a Series Rated Combination?
See the next two slides

Series Rating: Fuse/CB
Up to ISC= 200,000 Amp Available Short Circuit 400 A Class J Fuse 200,000 A Interrupting Rating 20 A XYZ Circuit Breaker Best CB Company 10,000 A Interrupting Rating Series Rated Combination 200,000 A. I.R. And here is a 20 ampere circuit breaker with an individual interrupting rating of 10 kA that is series rated with a 400 ampere Class J fuse with an individual interrupting rating of 300kA. The series rating for 200,000 amperes is the result of listing agency testing.

Available Short Circuit
Series Rating: CB/CB Series Rated Combination 65,000 A. I.R. 200 A ABC Circuit Breaker Best CB Company 65,000 A Interrupting Rating 20 A XYZ Circuit Breaker 10,000 A Interrupting Rating Up to ISC= 65,000 Amp Available Short Circuit Here is a 20 amp circuit breaker with a 10 kA individual interrupting rating that is series rated with an upstream 200 amp circuit breaker that has an individual interrupting rating of 65 kA. The series rating, also 65 kA, is the result of listing agency testing.

Background Series Ratings for Existing System
Building improvements and replacement transformers may have increased available short circuit currents to levels that exceeded existing circuit breakers’ interrupting ratings. Serious safety hazard Does NOT comply with NEC® 110.9 When buildings undergo improvements or if new transformers are installed, quite often the new available short circuit current exceeds the existing circuit breakers’ interrupting rating. This is a serious safety hazard and does not comply with NEC®

Circuit Breakers 14,000 A Interrupting Rating
Background BEFORE 500 KVA 480/277V 5 % Z 12,000 A Existing Equipment Circuit Breakers 14,000 A Interrupting Rating Slide shows original system with CB’s that have interrupting rating of 14,000A, which was sufficient for the original available fault current.

Circuit Breakers 14,000 A Interrupting Rating
Background BEFORE 500 KVA 480/277V 2% Z 30,000 A AFTER 500 KVA 480/277V 5 % Z 12,000 A Existing Equipment Circuit Breakers 14,000 A Interrupting Rating Slide shows original system that has been upgraded with lower impedance transformer. Available fault current now exceeds the interrupting rating of the existing CBs. This is a safety hazard. It occurs rather frequently in the modern economy. In many cases the building owner is not even aware of the change. In this case the available short circuit current increased from 12,000A to over 30,000A by a change of transformer. The KVA rating is the same in both cases. The only difference is the percent impedance of the transformer. In the after case, the existing circuit breakers are applied beyond their interrupting rating.

14,000A IR, 480V, Circuit Breaker 50,000 Available
Safety Hazard Available Short Circuit Current Beyond Circuit Breaker Interrupting Rating 14,000A IR, 480V, Circuit Breaker 50,000 Available These timed still photos illustrate the safety hazard when a circuit breaker is applied beyond its interrupting rating and then tries to interrupt this fault current.

Background Series Ratings for Existing System
Up until NEC® 2005 The only option…remove and replace the CB panel with a new CB or fusible switch panel with overcurrent protective devices with sufficient Interrupting ratings. Costly and Disruptive Prior to the 2005 NEC®, under this condition, the only option an owner had was to remove and scrap the existing circuit breaker panel and install a new circuit breaker or fusible switch panel that has overcurrent protective devices that are sufficient for the new available short-circuit current. This is very expensive and disruptive.

New Requirement 240.86(A) Series Rating
240.86(A) Selected Under Engineering Supervision in Existing Installations. The series rated combination devices shall be selected by a licensed professional engineer engaged primarily in the design or maintenance of electrical installations. The selection shall be documented and stamped by the professional engineer. This documentation shall be available to those authorized to design, install, inspect, maintain, and operate the system. This series combination rating, including identification of the upstream device, shall be field marked on the end use equipment. This is the new (A)

Series Ratings for Existing System
With the 2005 NEC® (A): A licensed professional engineer can determine if an upgrade of lineside fuses or circuit breakers can series rate with existing loadside circuit breakers. This may save owner significant money and provide a safer system Now for existing systems, a licensed professional engineer can determine if an upgrade of lineside fuses or circuit breakers can series rate with existing loadside circuit breakers. This new option may save an owner significant money and provide a safer system than if no action is taken when the available short-circuit current exceeds the installed circuit breakers’ interrupting rating.

Ensuring Compliance: Series Ratings for Existing Systems
Engineer: Analyzes if lineside fuse or circuit breaker provides protection to the downstream circuit breakers Provides stamped documentation that is readily available to those involved. The engineer provides the necessary analysis that insertion of a set of lineside fuses or circuit breaker can provide protection to the downstream circuit breakers. The documentation for the selection of series ratings for existing systems shall be stamped by the engineer and be readily available to those involved in the design, install, inspection, maintenance and operation of the equipment.

Methods For Existing Systems
There may be several analysis options for a licensed professional engineer to rectify situations where existing circuit breakers have inadequate interrupting ratings. Note: In some cases, a suitable method may not be feasible. New methods may surface in the future. Methods To Series Rate Existing Systems There may be several analysis options for a licensed professional engineer to rectify the situations where existing circuit breakers have inadequate interrupting ratings. In some cases, a suitable method may not be feasible. New methods may surface in the future. Some methods follow in the next two slides.

1. Check if new fused disconnect can be installed ahead of existing circuit breakers by using an existing, recognized series rated combination. 2. If existing system used series ratings with Class R fuses (RK5 Umbrella), analyze whether a specific Bussmann® Class RK1, J or T fuse may provide protection at the higher short-circuit current. 1. Check to see if a new fused disconnect can be installed ahead of the existing circuit breakers by using an existing recognized series rated combination. Even though the existing system may not take advantage of series ratings, if the existing circuit breakers are not too old, the panel may have a table or booklet that provides all the possible listed combinations of fuse-circuit breaker series ratings. 2. If the existing system used series ratings with Class R fuses, analyze whether a specific Bussmann® Class RK1, J or T fuse may provide the protection at the higher short-circuit current. The series ratings for panelboards that use lineside Class R fuses have been determined with special, commercially unavailable Class RK5 umbrella fuses. (Commercially unavailable umbrella fuses are only sold to electrical equipment manufacturers in order to perform equipment short-circuit testing) Actual, commercially available Bussmann® Class RK1, J or T fuses will have current-limiting let-through characteristics considerably less than the Class RK5 umbrella limits.

3. Supervise short circuit testing of lineside current-limiting fuses to verify protection is provided to circuit breakers that are identical to installed, existing circuit breakers. 4. Perform analysis to determine if current- limiting fuses installed on lineside of existing circuit breakers provide adequate protection for circuit breakers. Supervise short circuit testing of lineside current-limiting fuses to verify that protection is provided to circuit breakers that are identical to the installed, existing circuit breakers. 4. Perform an analysis to determine if a set of current-limiting fuses installed on the lineside of the existing circuit breakers provides adequate protection for the circuit breakers. For instance, if the existing equipment is low voltage power circuit breakers (approximately three cycle opening time), then the line-side fuse short-circuit let-through current (up, over, and down method) must be less than the circuit breaker’s interrupting rating. An appropriate analysis method has yet to be found for circuit breakers that clear in less than a 1/2 cycle. It is possible, but a practical analysis method based on present available circuit breaker data is not yet feasible.

Suggest Bussmann® Low-Peak® Fuses
For new installations, owners, designers, and contractors should consider using fusible switches in fully rated systems Low-Peak® fuses have 300,000A interrupting rating so changes to electrical system will not cause the available short circuit current to increase beyond their interrupting rating System reliability: no periodic maintenance and testing required on fuses to ensure their ability to operate as intended Suggestion for New Installations Design and install fusible switches in a fully rated system Use Bussmann® Low-Peak® Fuses on all the circuits: The owner does not have to unexpectedly make significant changes to the electrical system because the short-circuit current increased after the initial installation. KRP-C_SP, LPJ_SP, LPN-RK_SP, and LPS-RK_SP Low-Peak® Fuses have interrupting ratings of 300,000A. The owner does not have to have required periodic maintenance and testing performed on fuses to ensure their ability to operate as intended.

Solution Using Current Limiting Fuses
BEFORE AFTER 500 KVA 480/277V 5 % Z 12,000 A 500 KVA 480/277V 2% Z 30,000 A Bussmann Low Peak® Fuse Existing Equipment Circuit Breakers 14,000 A Interrupting Rating Current limiting fuses, such as Bussmann Low Peak® fuses, can be used to protect circuit breakers when available fault currents exceed the breakers’ interrupting ratings. A licensed professional engineer can select these fuses based upon a recognized series rated combination, or by using another approved method.

Series Ratings for New Systems
For new installations, the process remains the same as the 2002 NEC®: Tested Listed Marked Use the Tables and SPD publication For new installations, the process remains the same as the 2002 NEC®: the series rated combinations shall be tested, listed and marked for use with specific panel boards and switchboards. For fusible/CB series rated systems, use the tables by Bussmann fuses/CB manufacturer

Summary of Changes Series Ratings for Existing Systems
240.86(A) Series Ratings

2005 NEC® Article 100 Definition
Supplementary Overcurrent Protective Device. A device intended to provide limited overcurrent protection for specific applications and utilization equipment such as luminaires (lighting fixtures) and appliances. This limited protection is in addition to the protection provided in the required branch circuit by the branch circuit overcurrent protective device. A definition for Supplementary overcurrent protective device has been added to Article This definition has been added to help avoid serious misapplication of devices that have not been tested for general purpose usage. Supplementary overcurrent protective devices must not be applied where branch circuit overcurrent protective devices are required; unfortunately this unsafe misapplication is prevalent in the industry.

Supplementary Overcurrent Protective Devices
Examples Supplemental fuses are not branch circuit fuses and must not be confused with them. Supplemental protectors or “mini-breakers” are not branch circuit breakers. Branch circuit breakers are evaluated and listed to UL489 Molded Case Circuit Breakers and supplemental protectors are recognized to UL1077 Supplemental Protectors. The capabilities of UL1077 supplementary protectors are typically considerably less than UL489 circuit breakers. UL248-14 Supplemental Fuses UL1077 Supplemental Protectors (Mini-breakers)

Do not substitute where a branch circuit overcurrent protective device is required Capabilities and spacings can be inadequate compared to branch circuit OCPD Must be evaluated for appropriate application in every instance Must investigate differences and limitations for the specific application Supplementary overcurrent protective devices are not general use devices, as are branch circuit devices, and must be evaluated for appropriate application in every instance where they are used. Supplementary overcurrent protective devices are extremely application oriented and prior to applying the devices, the differences and limitations for these devices must be investigated and found acceptable.

Example of difference between UL489 circuit breaker and UL1077 supplemental protector: Spacings: UL /8” thru air, 1/2” over surface UL ” thru air, 2” over surface One example of the difference and limitations is that a supplementary overcurrent protective device may have spacings, creepage and clearance, that are considerably less than that of a branch circuit overcurrent protective device. Example: · A supplemental protector, UL1077, has spacings that are 3/8 inch through air and 1/2 inch over surface at 480V. · A branch circuit rated UL489 molded case circuit breaker has spacings that are 1 inch through air and 2 inches over surface at 480V.

Example of difference between UL489 circuit breaker and UL1077 supplemental protector: Time current characteristics UL1077 no standard overload characteristics UL489 standard overload characteristics Another example of differences and limitations is that branch circuit overcurrent protective devices have standard overload characteristics to protect branch circuit and feeder conductors. Supplementary overcurrent protective devices do not have standard overload characteristics and may differ from the standard branch circuit overload characteristics. Also, supplementary overcurrent protective devices have interrupting ratings that can range from 32 amps to 100,000 amps. When supplementary overcurrent protective devices are considered for proper use, it is important to be sure that the device's interrupting rating equals or exceeds the available short-circuit current and that the device has the proper voltage rating for the installation (including compliance with slash voltage rating requirements, if applicable).

10 reasons why UL1077 supplementary devices can not be used for branch circuit protection Not intended for, nor evaluated for branch circuit protection Spacings are inadequate Do not have standard overload characteristics Multipole, 3 phase UL1077 devices not evaluated for all types of overcurrents Most UL1077 devices tested with and rely upon upstream branch circuit device for protection Reasons Why Supplemental Protectors (UL1077 Devices) can not be used to Provide Branch Circuit Protection 1. Supplemental Protectors are not intended to be used or evaluated for branch circuit protection in UL1077 2. Supplemental protectors have drastically reduced spacings, compared to branch circuit protective devices, which depend upon the aid of a separate branch circuit protective device upstream 3. Supplemental protectors do not have standard calibration limits or overload characteristics performance levels and cannot assure proper protection of branch circuits 4. Multipole supplemental protectors for use in 3 phase systems are not evaluated for protection against all types of overcurrents 5. Most supplemental protectors are tested with a branch circuit overcurrent device ahead of them and rely upon this device for proper performance For a more in depth discussion see TECH TALK 3 found on

10 reasons why UL1077 supplementary devices can not be used for branch circuit protection 6. Not required to be tested by closing into fault 7. Not tested for calibration or reusability after fault interruption 8. Considerable damage allowed after short circuit interruption test 9. Not intended for branch circuit protection or disconnecting means 10. Not evaluated for energy let-thru or protection of conductors under short circuit current tests Reasons Why Supplemental Protectors (UL1077 Devices) can not be used to Provide Branch Circuit Protection 6. Supplemental protectors are not required to be tested for closing into a fault 7. Recalibration of a supplemental protector is not required and depends upon manufacturer’s preference. There is no assurance of performance following a fault or resettability of the device. 8. Considerable damage to a supplemental protector is allowed following short circuit testing. 9. Supplemental protectors are not intended to: · Provide Branch Circuit Protection · Be used as a Disconnecting Means 10. Supplemental protectors are not evaluated for short circuit performance criteria, such as energy let through limits or protection of test circuit conductors For a more in depth discussion see TECH TALK 3 found on

240.5(B) Protection of Flexible Cords, Flexible Cables and Fixture Wires
Prior to 2005 NEC®, supply cords of listed appliances, portable lamps, and extension cords assumed protected by branch circuit device However, many fires caused by small wire With 2005 NEC, these supply cords are considered protected when applied within listing requirements NRTLs & cord and equipment manufacturers determine if small wire protected If specific cords or equipment has poor record, protection may be required If protection needed, could be fuse, GFCI, AFCI, LCDI or combination Prior to the 2005 NEC® the supply cords of listed appliances, portable lamps, and listed extension cord sets were “assumed” to be protected by the branch circuit overcurrent protective device. There has been a change to the 2005 NEC® that removes this assumption. The new requirement considers these cords to be protected when applied within the listing requirements. There has been a lot of focus on preventing fires due to arcing faults in recent code cycles. This focus has brought about the requirements for AFCI protection on bedroom circuits. Many of the studies that were used to substantiate the AFCI requirement show that as many as 60% of all electrical fires started on the load side of the outlet. The fires start in the extension cords, supply cords, and appliances. This new requirement places the responsibility on the cord/equipment manufacturers and product safety standards to evaluate the protection of the appliances and cords, and any possible necessity for supplemental overcurrent protection. Nationally Recognized Testing Laboratories (NRTLs) and the equipment manufacturers will now have to determine if the small wire is properly protected. Some equipment that has never caused fires will not be affected. But other equipment that has a poor record for causing fires will likely be required to provide the protection of their cords. That protection might come in the form of supplementary fuses, AFCIs, GFCIs, LCDIs, or a combination of two or more of these.

240.5(B) Protection of Flexible Cords, Flexible Cables and Fixture Wires
One solution - fused line cords Cost effective Good protection Used extensively in UK and Japan Fused line cords are one of the possible and least costly solutions for protecting line cords of equipment. This is currently a common practice for holiday lights. This method is also widely used in the UK (Bussmann P/N TDC180 shown in the photo) and Japan. Fused plug

240.60(D) Renewable Fuses Now Replacement Only
Class H cartridge fuses of the renewable type shall only be permitted to be used for replacement in existing installations where there is no evidence of overfusing or tampering. Not to be used on new installations Reason: renewable fuses have only 10,000A interrupting rating The 2005 NEC® has new requirements that prohibit the use of Class H renewable fuses for new installations. The reasoning given for this restriction was that renewable fuses were posing significant safety issues. The code making panel statement did not support the claims of the safety issues, however, they chose to support the proposal because of the minimal 10,000 amp interrupting rating. Renewable fuses that are applied within their ratings and where there is no evidence of tampering are permitted for replacement in existing installations

Supports overcurrent protective devices with high interrupting rating For new equipment use: Low Peak® Fuses 300,000A IR LPJ_SP KRP_C_SP LPS-RK_SP & LPN-RK_SP LP-CC (200,000A IR) CUBEFusesTM 300,000A IR TCF Additional fuse types available with high IR This new requirement supports the use of devices with higher interrupting ratings. New equipment should be installed using Fusetron® (RK5) which have a 200,000A IR, or preferably Low-Peak® (RK1, J, CC or L) fuses which have a 200,000A IR for LP-CC fuses and 300,000A IR for the others. It is also important if Class R fuses are used, to install switches with rejection fuse clips, so that Class H fuses cannot be used for later replacement. Class J, L, T, CC, and G fuses as well as the CUBEFuseTM mounting are all physical size rejecting so only that respective Class of fuse can be installed. This ensures the installation maintains its high interrupting rating.

Modern current limiting fuses with high interrupting rating also provide: Best equipment protection Selective coordination Reliability over life of system Minimal maintenance Possible arc flash hazard reduction Physical size rejecting features In addition to the highest interrupting ratings of all overcurrent protective devices, modern current-limiting fuses provide: - The best equipment protection - The easiest overcurrent protective devices to selectively coordinate - Reliable overcurrent protection over the life of the system - Minimal maintenance - The best reduction of the arc flash hazard when the arcing current is within the current limiting range - Physical size rejection features. For instance, only Class J fuses can be inserted in fuse mountings for Class J.

410.73(G) Disconnecting Means for Electric Discharge Lighting (1000V or less)
2005 NEC® new section requiring disconnecting means for certain types of luminaires: That use double-ended lamps Indoor other than dwellings Ballasts that can be serviced in place Disconnecting means accessible to qualified person prior to servicing the ballast Effective Jan. 1, 2008 Rationale: safer system for electricians The 2005 NEC® has a new article requiring individual disconnecting means for ballasted electric discharge lighting fixtures that have double ended lamps, or those that are fed by multiwire branch circuits (with some exceptions). Industry data has shown that a leading cause of fatalities for electricians is electrocution while working on 277V lighting systems. Electricians are often pressured to change out ballasts while the circuits are energized to avoid removing illumination from an area. When the electrician gets to the wire nut with three white wires (neutral), the thought is that these are grounded conductors, and therefore are not hazardous. The electrician opens the wire nut and gets between two of the white wires, which can result in shock or electrocution. These white wires carry the unbalanced load current from all phases. This new requirement will allow electricians to de-energize a ballasted luminaire without removing illumination to an entire area. Then they can safely change out the ballast without being exposed to a shock hazard. This change has been given an effective date of January 1st, 2008 to allow manufacturers time to develop products for this application.

430.52(C)(6) Self-Protected Combination Controller Single-Pole Interrupting Capability Limitation
New 2005 NEC® 430.52(C)(6) FPN: Proper application of self-protected combination controllers on 3-phase systems, other than solidly grounded wye, particularly on corner grounded delta systems, considers the self-protected combination controllers’ individual pole-interrupting capability. Self-protected combination controllers are intended to provide motor overload, and motor branch circuit short-circuit and ground fault protection. They are essentially the same as circuit breakers when it comes to short-circuit protection. And like circuit breakers, they have limitations on how much short-circuit current a single pole can interrupt (individual pole interrupting capability). For this reason a FPN was added to the 2005 NEC® that matches the FPN added to for the 2002 NEC® for circuit breakers. While the FPN is not a requirement it does alert users that proper application of these devices takes the individual pole interrupting capability into consideration.

430.52(C)(6) Self-Protected Combination Controller Single-Pole Interrupting Capability Limitation
This limitation can be a safety hazard The single-pole interrupting capability is not marked on the device Must check UL508 Standard Device 0 to 200 hp up to 600V: tested only for 8,660A single-pole short circuit current interruption, even though the device may have a three-phase short circuit current rating of 65,000A. This single-pole interrupting capability for self-protected combination controller can be a safety hazard. There can be a safety hazard. The single-pole interrupting capability is marked on the device. Self-protected combination controllers are listed to UL Table 82A.3 specifies the short circuit test values of one pole as 8,660 amps for 0 to 200 hp devices rated up to 600 volts. Self-protected combination controllers may not be able to safely interrupt single-pole faults above these values. Per 110.3(B), these devices must not be used in an application where they are subjected to more fault current than specified in UL 508 (8,660A for 0 to 200 hp devices rated up to 600 volts). For this reason a FPN was added to the 2005 NEC® that matches the FPN added to for the 2002 NEC® for circuit breakers. While the FPN is not a requirement it does alert users that proper application of these devices takes the individual pole interrupting capability into consideration.

430.83(E) Slash Voltage Rating for Motor Controllers
New 2005 NEC ® 430.83(E) Applications. A motor controller with a slash rating, such as 120/240V or 480Y/277, shall be permitted to be applied in a solidly grounded circuit where the nominal voltage of any conductor to ground does not exceed the lower of the two values of the motor controller’s voltage rating and the nominal voltage between any two conductors does not exceed the higher value of the motor controller’s voltage rating…” The 2005 NEC® section covering voltage ratings for motor controllers was changed to address the proper application of slash-rated devices. A slash-rated motor controller is one with two voltage ratings separated by a slash, such as 480Y/277 volt. The change was the addition of the words “solidly grounded”. This was needed to emphasize that slash-rated devices are not appropriate for use on corner grounded delta, resistance-grounded and ungrounded systems. This typically pertains to the self-protected combination controllers mentioned in the previous section. Most of them are “dual listed.” Dual listed controllers will have one listing as a manual motor controller that has a straight 480 volt rating. When used as a manual motor controller they can be used any 480 volt system, but they must be protected by a fuse or circuit-breaker. Dual listed devices also have a second listing as a self-protected motor controller. The self-protected starter listing is nearly exclusively rated 480Y/277. These slash-rated devices cannot be used on corner-grounded delta, resistance grounded, or ungrounded systems. Where it is possible for full phase-to-phase voltage to appear across only one pole, a slash-rated device is not acceptable. These self-protected starters are typically listed with a straight 480 volt rating when utilized as a manual motor controller. As such, they can be used on other than solidly grounded systems, but only for their on/off function and overload protection. When slash-rated devices such as self-protected motor controllers are installed in equipment, it limits the application of the equipment to solidly grounded wye systems. The equipment nameplate must also be marked with the slash-rating (e.g. 480Y/277) to clearly indicate that it is limited by the type of grounding system. This limits the entire equipment or panel to solidly grounded systems only. The advantage of fuses is that they are tested with full voltage across the fuse, and therefore are not limited by the type of grounding systems. Equipment that has slash-rated devices for short-circuit protection can often be retrofitted with fuses (such as LP-CC fuses with the OPM-NG holder) to eliminate the limitations.

480Y/277 slash voltage rating
Motor Controller 480Y/277 slash voltage rating 480 volts Line-to-line 480Y/277 Volt Three phase Four wire Solidly grounded wye system A B C N Now, if we have a 480Y/277V, three phase, four wire solidly grounded wye system and apply this 480/277V motor controller: The smaller of the two ratings is for overcurrents at line-to-ground voltages, meant to be cleared by one pole of the device. In this example, the motor controller lower rating is 277 volts and the system line to ground voltage is 277 volts. The larger of the two ratings is for overcurrents at line-to-line voltages, meant to be cleared by two or three poles of the motor controller. In this example the system’s line to line voltage is 480 volts and the motor controller line to line voltage rating is 480 volts. Ground 277 volts Line-to-ground

Slash Rated Exercise Can 480Y/277 Controller Be Used? System Voltage
Secondary System Type L-L Volt L-G Volt 480Y/277 Solidly Grounded WYE 480 277 Yes No 480 Resistance Grounded WYE 480 277 Yes No 480 Delta Corner Grounded B Phase 480 480 Yes No Before we proceed let’s test your knowledge. For each of the four separate examples shown answer yes or no as to whether a 480Y/277 volt motor controller can be used in compliance with (E). The first is a 480Y/277 volt, solidly grounded system with 480 volts line to line and 277 volts line to ground. Can a 480Y/277 volt motor controller be used? Using your mouse, click on your answer either yes or no. 480 Delta Ungrounded 480 * Yes No * Ungrounded delta systems - phase conductors are capacitively coupled to ground

Secondary System Type L-L Volt L-G Volt 480Y/277 Solidly Grounded WYE 480 277 Yes No 480 Resistance Grounded WYE 480 277 Yes No 480 Delta Corner Grounded B Phase 480 480 Yes No Let’s check your response. The first is a 480Y/277 volt, solidly grounded system with 480 volts line to line and 277 volts line to ground. Can a 480Y/277 volt motor controller be used? The answer is Yes, since it is a solidly grounded system, the lower device rating of 277 volts equals the system line to ground voltage of 277 and the higher device rating of 480 equals the line to line system voltage of 480 volts. Proceed and do the next one; the resistance grounded wye. click on your answer. 480 Delta Ungrounded 480 * Yes No * Ungrounded delta systems - phase conductors are capacitively coupled to ground

Secondary System Type L-L Volt L-G Volt 480Y/277 Solidly Grounded WYE 480 277 Yes No 480 Resistance Grounded WYE 480 277 Yes No 480 Delta Corner Grounded B Phase 480 480 Yes No Let’s check your second response. The answer is No, because it is a resistance grounded system which is not defined as a “solidly grounded system”. A slash rated device does not comply. Proceed and do the third one; corner grounded delta. click on your answer. 480 Delta Ungrounded 480 * Yes No * Ungrounded delta systems - phase conductors are capacitively coupled to ground

Secondary System Type L-L Volt L-G Volt 480Y/277 Solidly Grounded WYE 480 277 Yes No 480 Resistance Grounded WYE 480 277 Yes No 480 Delta Corner Grounded B Phase 480 480 Yes No Let’s check your third response. The answer is No. This is a corner grounded system delta. Even though it is solidly grounded, the lower device rating of 277 volts is less than the system line to ground voltage of 480 volts. So a slash rated device does not comply. Proceed and do the fourth one; delta ungrounded. click on your answer. 480 Delta Ungrounded 480 * Yes No * Ungrounded delta systems - phase conductors are capacitively coupled to ground

Secondary System Type L-L Volt L-G Volt 480Y/277 Solidly Grounded WYE 480 277 Yes No 480 Resistance Grounded WYE 480 277 Yes No 480 Delta Corner Grounded B Phase 480 480 Yes No Let’s check your fourth response. The answer is No. This is not a solidly grounded system so a slash rated device does not comply. 480 Delta Ungrounded 480 * Yes No * Ungrounded delta systems - phase conductors are capacitively coupled to ground

Slash Voltage Rating System must be solidly grounded
Larger device voltage rating greater than system L-L voltage Smaller device voltage rating greater than system L-G voltage 480Y / 277 V

Single-Pole Interrupting Capability and Slash Voltage Rating Examples
The next seven slides demonstrate the limitations of single-pole interrupting capabilities and slash voltage rating. These are examples with circuit breakers. The same issues are applicable to self protected combination controllers for single-pole interruption and slash voltage ratings and motor controllers for slash voltage ratings The next seven slides after this one demonstrate the limitations of single-pole interrupting capability. These examples are circuit breakers, but the same issues apply to self protected combination controllers for single pole interruption and slash voltage ratings, and motor controllers for slash voltage ratings.

Solidly Grounded WYE System
SERVICE PANEL BRANCH PANEL Steel Conduit A A 277V 480V 277V B 277V B C C We are going to examine how different systems must be analyzed for circuit breaker single pole interrupting capabilities. The first system we will look at is the solidly grounded wye system, which is by far is the most common type of electrical system. This system is typically delta connected on the primary and has an intentional solid connection between the ground and the center of the wye connected secondary (neutral). The grounded neutral conductor carries single-phase or unbalanced three-phase current. This system lends itself well to industrial applications where 480V(L-L-L) three-phase motor loads and 277V(L-N) lighting are required. N N

Single Pole Must Interrupt Fault Current
Solidly Grounded WYE System Single Pole Must Interrupt Fault Current SERVICE PANEL BRANCH PANEL Steel Conduit A A Fault to Conduit 277V 480V 277V B 277V B C C In solidly grounded wye systems, the first low impedance fault to ground is generally sufficient to open the overcurrent device on the faulted leg. (Mouse Click) In the circuit shown, this fault current causes the branch circuit overcurrent device to clear the 277 volt fault. Because the branch circuit device will clear the fault with only 277 volts across one pole, a slash-rated 480Y/277 volt circuit breaker is perfectly acceptable. However, what about the single pole interrupting capability? This system requires compliance with single-pole interrupting capability for 277 volt faults on one pole. If the overcurrent devices have a single-pole interrupting capability adequate for the available short-circuit current, then the system meets NEC We worked through an example of a 20 ampere, 480Y/277 circuit breaker earlier. This breaker is single pole tested by UL to interrupt 10,000 amperes. N N

Corner Grounded Delta System
SERVICE PANEL BRANCH PANEL Steel Conduit A A 480V 480V B C 480V B C The system shown has a delta-connected secondary and is solidly grounded on the B-phase. If the B-phase should short to ground, no fault current will flow because it is already solidly grounded.

Single Pole Must Interrupt Fault Current
Corner Grounded Delta System Single Pole Must Interrupt Fault Current SERVICE PANEL BRANCH PANEL Steel Conduit A A Fault to Conduit 480V 480V B C 480V B C If either Phase A or C is shorted to ground, only one pole of the branch-circuit overcurrent device will see the 480V fault as shown. In this example, a fault from phase A to the steel conduit occurs. The fault current path is through the steel conduit and equipment enclosures back to the service. At the service the grounding jumper provides the path to the grounded conductor which completes the circuit. Take the time to follow the current path. (Mouse Click) The fault current flows through the steel conduit, through the steel of the branch circuit panel, through the steel conduit between the branch and service panels, through the steel of the service panel, over the grounding jumper to the grounded conductor of the system, through the transformer winding, and to the point of the fault. You can see that the branch-circuit circuit breaker’s A phase has to clear this fault current on its own. Phase B and Phase C of this circuit breaker do not have any fault current flowing through them. A slash rated 480Y/277 volt circuit breaker could not be utilized on this 480 volt corner-grounded delta circuit because the voltage to ground of 480 volts, exceeds the lower of the two ratings of 277 volts. This system also requires compliance with single-pole interrupting capabilities for 480 volt faults on one pole because the branch-circuit circuit breaker would be required to interrupt 480 volts with only one pole. A disadvantage of Corner-Grounded Delta systems is the inability to readily supply voltage levels for fluorescent or HID lighting (277V). Installations with this system require a V transformer to supply 120V lighting. Another disadvantage, as given on page 33 of IEEE Std , Section 1.5.1(4) (Green Book) is " the possibility of exceeding interrupting capabilities of marginally applied circuit breakers, because for a ground fault, the interrupting duty on the affected circuit breaker pole exceeds the three-phase fault duty."

UL Single Pole Short-Circuit Test
Single Pole Interrupting Capability UL 489 Circuit Breaker Procedure UL Single Pole Short-Circuit Test CB Frame Rating 480/277V 480V 100 A Maximum 10,000 Amps 8,660 Amps 101 – 800 A. 10,000 Amps 8,660 Amps As an example of single-pole interrupting capability in a typical installation, consider a common three-pole, 20 amp, 480 volt circuit breaker. Assume this three pole, 20 amp circuit breaker has a three-pole interrupting rating of 65,000 amperes. Referring to the table on the slide, this breaker has an 8,660 ampere single-pole interrupting capability for 480 volt faults across one pole. If the available line-to-ground fault current exceeds 8,660 amps at 480 volts, such as might occur on the secondary of a 1000 KVA, 480 volt, corner-grounded delta transformer, the circuit breaker may be misapplied. In this case, the breaker manufacturer must be consulted to verify interrupting ratings and proper application. Example: 20 A, 480V CB having 65,000 A.I.R. (3 Pole Test). Single pole tested at 8,660 Amps

480 Volt, 25,000 Amp Line to Ground 4 Feet 4/0 225 Amp, 480 V
Single Pole Test UL489 tests single pole at only 8660A 225 Amp, 480 V Circuit Breaker 35, 000 Amp Three Phase Interrupting Rating 4 Feet 4/0 To better understand the importance of investigating and properly applying single pole interrupting capabilities let’s take a look at photos from a test where the single pole fault current exceeded the circuit breaker’s single pole interrupting rating. In this test, a 225 ampere, 480 V rated circuit breaker will be tested. There will be a faulted circuit on one pole of 480 volts with an available of 25,000 amperes. This circuit breaker has a three pole UL interrupting rating of 35,000 amperes. The test was recorded on VHS video tape at normal speed. These photos were reproduced from the VHS tape. Photos on following slide

This is the test set up prior to the test circuit being closed
This is the test set up prior to the test circuit being closed. The next few slides are linked. During the test the board with the circuit breaker moved due to the mechanical forces of the fault current.

2005 Code Changes THE END This concludes the presentation. Thanks for your participation.

Suggestion on How to Use

Similar presentations

Presentation on theme: "Suggestion on How to Use"— Presentation transcript:

Similar presentations

About project

Feedback

Log in

Auth with social network:

Suggestion on How to Use

Similar presentations

Presentation on theme: "Suggestion on How to Use"— Presentation transcript:

Similar presentations

About project

Feedback