Suggestion on How to Use

Suggestion on How to Use
Industry Trainers are encouraged to use this material in their sessions Download the presentation file Print the Notes pages and read them as you view the presentation in the “Slide Show” view. In this way you see the slides in large format and have animation (when available) Suggestion on How to Use Download the presentation file. Print the Notes pages and read them as you view the presentation in the “Slide Show” view. In this way you see the slides in large format and have animation (when available).

Motor and Motor Circuit Protection

Agenda Motor Circuit Characteristics Protection from Overcurrents Motor Circuit Requirements Sizing OCPD’s Back-up Overload Protection Type 2 Protection This presentation is designed to give you a better understanding of how a motor circuit operates and how you can protect the components involved in the motor circuit from overloads and short circuits.

How does a motor operate? Starting Normally What do we protect against? Overload Short-Circuit So how does a motor operate and what types of current characteristics can it experience?

Normal Operating Current
1000 100 10 1 0.1 0.01 Time in Seconds Current in Amperes Normal Operating Current Motor Inrush Curve The starting current of a motor is also what is known as the inrush current for the motor. Getting the rotor inside the motor to begin to turn requires more current than is needed to keep the rotor spinning. Initially, this inrush current is typically between 4 to 8 times the normal operating current and can last for several seconds. As the rotor arrives to a constant speed, the current needed to turn the rotor gradually subsides to a constant value as well. You can see this depicted in the curve. An initial large amount of current subsides after a few seconds to a normal operating current. The normal operating current is most commonly referred to as the FLA(Full Load Amperes) of the motor. This current operates at a nearly constant value for a continuous duty operation to keep the rotor turning. Inrush Current

300 % Overload Time in Seconds Current in Amperes 1000 100 10 1 0.1
0.01 Time in Seconds Current in Amperes 300 % Overload An overload condition will occur when the rotor has difficulty turning and draws more amperage to keep it turning than it normally would. An overload is most often between the FLA and 6 times the normal operating current. For example if a conveyor belt becomes jammed and does not allow the rotor to turn, the motor will draw about as much amperage as it would on startup to try to get the rotor to turn. As long as the rotor does not turn, this increased current will continue to flow. The key thing to remember in an overload condition is that the current flows through the normal circuit path. Continued subjection to an overload current will cause excess heating in the motor and the motor circuit. If the overcurrent protective device does not operate in a timely manner, a motor winding could short out, or winding insulation damage could lead to a short circuit later.

Short Circuit Time in Seconds Current in Amperes 1000 100 10 1 0.1
0.01 Time in Seconds Current in Amperes Short Circuit A short circuit can occur in many different ways and can be many hundred times larger than the normal operating current. The main thing to acknowledge with a short circuit is that the current will travel outside the normal path. In the example here a line to line fault occurred prior to entering the motor, causing a very large amount of current to travel through the remainder of the motor circuit. In the case of a short circuit, the overcurrent protective device must be sized properly to be able to protect the Motor Circuit components from the disastrous effects of the short circuit current.

Motor Circuit Requirements(NEC®)
To Supply M Motor Branch Overload (Part IX) Disconnecting means 430.52 Branch-Circuit Short-Circuit Protection 430.32 Overload Protection Now let’s take a look at what is required for a motor circuit from the NEC. We will also be able to look at how the Overcurrent Protective Devices are required to be sized.

NEC® Location(Of Disconnecting Means) (A) In sight from Controller Branch-Circuit Short-Circuit Disconnect (B) In sight from Motor Manual Motor Controller “Suitable as Motor Disconnect” Exceptions provided if (A) is lockable in open position. Section outlines the location of the disconnecting means. Part A requires a disconnecting means in sight from(within 50ft.) the motor controller. This disconnect will be the Branch-circuit short-circuit disconnect. Part B requires a disconnecting means in sight from the motor. This can also be the Branch-circuit short-circuit disconnect. If however, the motor is not in sight from the branch-circuit short circuit disconnect, an additional disconnect is required to be within sight of the motor. This can be the same type of disconnect that is used for the Branch-circuit short-circuit disconnect, it can be a non-fused disconnect, or it can be a manual motor controller if the MMC is marked “suitable as a motor disconnect”.

1999 NEC® Code M Lockable Disconnecting Means
Barrier, wall or isle with an obstruction Controller Up through the 1999 code, the exception was that if the branch-circuit short-circuit disconnecting means was Lockable, you did not have to have a disconnecting means within sight of the motor. The circuit diagram here would have been acceptable. M

Requirement since 2002 NEC® Code
In sight (of controller) disconnecting means ahead of controller required per (A) Barrier, wall or isle with an obstruction In sight motor disconnecting means required per (B) The NEC now requires the second disconnecting means in all instances except for the two following exceptions. There are two exceptions to this additional disconnect requirement that can be used so long as the Branch-circuit Short-circuit disconnect is capable of being locked in the open position. Exception (a) is: “where such a location of the disconnecting means is impracticable or introduces additional or increased hazards to persons or property” such as “Informational Note: … …motors rated in excess of 100hp, multimotor equipment, submersible motors, motors associated with variable frequency drives, and motors located in hazardous (classified) locations.” Exception (b) is: “in industrial installations, with written safety procedures, where conditions of maintenance and supervision ensure that only qualified persons service the equipment” Controller M

NEC® Branch-Circuit Short-Circuit Protection (B) Must handle starting current (C) Rating or Setting (1) Table Exception 1: Next Higher size is permitted if the values from table do not correspond to a standard size This section states that whatever device is selected it must be able to handle the starting current or inrush current. It also refers to Table for maximum sizing and the exception allows the next standard size if the calculation does not land on a standard amperage size.

Table Maximum Rating* Non time-delay Fuse1 Dual-Element (Time-Delay) Fuse Instantaneous Trip Breaker Inverse Time Breaker 300% 175% 800% 250% Table allows Non-time delay fuses up to 300%, Dual element time-delay fuses up to 175%, Instantaneous Trip Breakers(MCPs) up to 800% and an inverse time(thermal magnetic) CBs up to 250%. 1Non-Time-Delay also applies to Class CC fuses *Single-phase motors, AC polyphase motors other than wound-rotor, squirrel cage-other than Design B energy-efficient

NEC® (C)(1) Exception 2: If Motor Unable to Start, then size according to following, or next smaller size 400% 300% 225% Inverse Time Breaker< 100A Inverse Time Breaker> Dual-Element (Time-Delay) Fuse Non time-delay Fuse1 A Fuse If by any chance the maximum sizing in table (or the next standard size per Exc No. 1) does not allow the motor to start, Exception No. 2 allows this sizing as a maximum. The next smaller size must be utilized if the calculation doesn’t result in a standard size. 1Non-Time-Delay also applies to Class CC fuses

NEC® (Overload Protection) (a) More than 1 Horsepower. (1) A separate overload device that is responsive to motor current. This device shall be selected to trip or rated at no more than the following percent of the motor nameplate full-load current rating. Motors with a marked service factor 1.15 or greater % Motors with a marked temperature rise 40 °C or less % All other motors % An overcurrent device sized in accordance with the above information could be used for overload protection. This means that if a fuse or circuit breaker can be sized in accordance with the above, it can be used for overload protection.

MOTOR CIRCUIT DEVICES Now let’s take a look at how these devices stack up and how they are used to protect the motor circuit.

What OCPD(s) can be used in a motor circuit? Fuse Circuit Breaker MCP Overload relay

Motor Inrush Curve Time in Seconds Current in Amperes 1000 100 10 1
0.1 0.01 Time in Seconds Current in Amperes Motor Inrush Curve Here is the inrush curve for a 1/3 Hp, 208V, 3Ø motor, with a nameplate FLA of 1.4 Amps.

MCP at minimum setting Time in Seconds Current in Amperes 1000 100 10
0.1 0.01 Time in Seconds Current in Amperes MCP at minimum setting This is the time-current curve for an MCP. The MCP is an instantaneous only circuit breaker. It does not have the bimetallic element that is used for thermal(overload) sensing.

MCP at minimum setting Motor Inrush Curve Time in Seconds
1000 100 10 1 0.1 0.01 Time in Seconds MCP at minimum setting Motor Inrush Curve If we look at the two curves together we will see that there can be a problem with an MCP at its minimum setting. It overlaps the inrush curve and will not allow the motor to start. Current in Amperes

MCP at maximum setting Time in Seconds Current in Amperes 1000 100 10
0.1 0.01 Time in Seconds Current in Amperes MCP at maximum setting The MCP can then be dialed up to its maximum setting to allow the motor to start.

MCP at maximum setting Motor Inrush Curve Time in Seconds
1000 100 10 1 0.1 0.01 Time in Seconds Current in Amperes MCP at maximum setting Motor Inrush Curve Looking at the Two curves together now we see that the motor will be allowed to start. We also see that if a short-circuit were to occur, the MCP will be able to open the circuit.

300 % Overload Time in Seconds Current in Amperes 1000 100 10 1 0.1
0.01 Time in Seconds Current in Amperes 300 % Overload But what about if we have an overload condition, such as this 300% overload? What should we be concerned with?

Motor Damage Curve Time in Seconds Current in Amperes 1000 100 10 1
0.1 0.01 Time in Seconds Current in Amperes Motor Damage Curve The motor damage curve is what needs to be looked at when considering an overload condition.

Motor Damage Curve 300 % Overload Time in Seconds Current in Amperes
1000 100 10 1 0.1 0.01 Time in Seconds Current in Amperes Motor Damage Curve 300 % Overload If an overload occurs, we must take the circuit offline before the overload reaches the motor damage curve.

MCP at maximum setting Motor Damage Curve 300 % Overload
1000 100 10 1 0.1 0.01 Time in Seconds Current in Amperes MCP at maximum setting Motor Damage Curve 300 % Overload Looking at the MCP at its maximum setting we see that it cannot provide protection against an overload condition. Therefore the motor would be damaged in this situation.

15A Circuit Breaker Time in Seconds Current in Amperes 1000 100 10 1
0.1 0.01 Time in Seconds Current in Amperes 15A Circuit Breaker What about an inverse time circuit breaker?

15A Circuit Breaker Motor Inrush Curve Time in Seconds
1000 100 10 1 0.1 0.01 Time in Seconds Current in Amperes 15A Circuit Breaker Motor Inrush Curve It will allow the motor to start and provides a degree of short circuit protection.

15A Circuit Breaker Motor Damage Curve 300 % Overload Time in Seconds
1000 100 10 1 0.1 0.01 Time in Seconds Current in Amperes 15A Circuit Breaker Motor Damage Curve 300 % Overload But what about the overload? You can see that it will not provide the overload protection needed.

NON-2 Amp Time in Seconds Current in Amperes 1000 100 10 1 0.1 0.01
Let’s look at a fuse. Specifically in this case a NON 2, which is a 2 amp, non-time delay fuse.

NON-2 Amp Motor Inrush Curve Time in Seconds Current in Amperes 1000
0.1 0.01 Time in Seconds Current in Amperes NON-2 Amp Motor Inrush Curve But as you can see, the motor will not be able to start. So we must increase the size of the fuse.

NON-5 Amp Time in Seconds Current in Amperes 1000 100 10 1 0.1 0.01
Let’s look at a NON 5 which is a 5 amp, non-time delay fuse. Current in Amperes

NON-5 Amp Motor Inrush Curve Time in Seconds Current in Amperes 1000
0.1 0.01 Time in Seconds Current in Amperes NON-5 Amp Motor Inrush Curve This would allow the motor to start, but what about the overload condition?

NON-5 Amp Motor Damage Curve 300 % Overload Time in Seconds
1000 100 10 1 0.1 0.01 Time in Seconds Current in Amperes NON-5 Amp Motor Damage Curve 300 % Overload A non-time delay fuse cannot provide protection against this overload.

Overload Relay Time in Seconds Current in Amperes 1000 100 10 1 0.1
0.01 Time in Seconds Current in Amperes Overload Relay What about an overload relay? It is designed to protect against overload conditions.

Motor Inrush Curve Overload Relay Time in Seconds Current in Amperes
1000 100 10 1 0.1 0.01 Time in Seconds Current in Amperes Motor Inrush Curve Overload Relay It allows the motor to start.

Motor Damage Curve 300 % Overload Overload Relay Time in Seconds
1000 100 10 1 0.1 0.01 Time in Seconds Current in Amperes Motor Damage Curve 300 % Overload Overload Relay And will take the system offline if an overload condition occurs prior to reaching the motor damage curve. So the overload relay will provide the overload protection for the motor.

MCP at maximum setting Motor Damage Curve 300 % Overload
1000 100 10 1 0.1 0.01 Time in Seconds Current in Amperes MCP at maximum setting Motor Damage Curve 300 % Overload Overload Relay MCP in conjunction with the overload relay provides both overload protection and short circuit protection required by NEC.

15A Circuit Breaker Motor Damage Curve 300 % Overload Overload Relay
1000 100 10 1 0.1 0.01 Time in Seconds Current in Amperes 15A Circuit Breaker Motor Damage Curve 300 % Overload Overload Relay CB in conjunction with the overload relay provides both overload protection and short circuit protection required by NEC.

NON-5 Amp Motor Damage Curve 300 % Overload Overload Relay
1000 100 10 1 0.1 0.01 Time in Seconds Current in Amperes NON-5 Amp Motor Damage Curve 300 % Overload Overload Relay Non time delay fuse in conjunction with the overload relay provides both overload protection and short circuit protection required by NEC.

FRN-R-1-6/10 Time in Seconds Current in Amperes 1000 100 10 1 0.1 0.01
But what about the dual element time delay fuse? How does it stack up? Sizing it for overload protection we will see that the 1-6/10 amp fuse would be the proper size.

FRN-R-1-6/10 Motor Inrush Curve Time in Seconds Current in Amperes
1000 100 10 1 0.1 0.01 Time in Seconds Current in Amperes FRN-R-1-6/10 Motor Inrush Curve It will allow the motor to start.

FRN-R-1-6/10 Motor Damage Curve 300 % Overload Time in Seconds
1000 100 10 1 0.1 0.01 Time in Seconds Current in Amperes FRN-R-1-6/10 Motor Damage Curve 300 % Overload It can open the circuit before the motor is damaged from an overload and it provides the short-circuit protection needed. So a dual-element time delay fuse can provide both short circuit and overload protection if sized properly.

Optimal Branch Circuit Protection (Back-up Overload Protection): 125% or up of FLA - FRN/FRS 130% or up of FLA- LPN/LPS 150% or up of FLA- LPJ 200% or up of FLA- LP-CC Keep in mind that for short circuit protection the sizing from the NEC is maximum sizing. Different manufacturer’s may have recommendations for what is called optimal sizing. These are an example of how certain Bussmann fuses can be sized for optimal sizing. Note:Class CC fuses are considered to be non time delay fuses and can be sized to a maximum of 300% for branch-circuit short-circuit protection.

FRN-R-1-8/10 Time in Seconds Current in Amperes 1000 100 10 1 0.1 0.01
Using the optimal sizing recommendation of 125% of FLA, or next size larger, we would end up with an FRN-R-1-8/10.

FRN-R-1-8/10 Motor Damage Curve Overload Relay Time in Seconds
1000 100 10 1 0.1 0.01 Time in Seconds Current in Amperes FRN-R-1-8/10 Motor Damage Curve Overload Relay By sizing the fuse this way you can provide “back-up” overload protection for the overload relay.

FRN-R-1-8/10 Motor Damage Curve 300 % Overload Overload Relay
1000 100 10 1 0.1 0.01 Time in Seconds Current in Amperes FRN-R-1-8/10 Motor Damage Curve 300 % Overload Overload Relay Remembering that the overload relay is the main defense against an overload, if an overload were to occur the overload relay should open the circuit. But by sizing the fuse for backup overload protection, if something were to happen to the overload relay and it could not operate properly, the fuse would be the second line of defense and open the circuit.

Single-Phasing Single phasing is the opening of one phase of a three phase circuit. What about single-phasing? One of the common misconceptions about fuses is that they cause single phasing. While it is possible for the fuse to open up one phase and cause a single phase condition to occur, the fuse is not the only cause of single-phasing.

Primary Single Phasing
Primary wire broken by: Storm - Wind - Ice - Sleet - Hail - Lightning Vehicle or Plane Striking Pole Falling Tree Limbs Construction Mishaps Primary wire burned out from short-circuit created by animals(i.e. squirrel to ground) A primary single phase is the opening of one phase of the system feeding the incoming delta-wye or wye-delta transformer.

Defective contacts on primary breaker - failure to make up on all 3 poles. Failure of 3 shot automatic reclosers to make up on all 3 poles. Open pole on 3Ø auto. voltage tap changer Open winding in one phase of transformer Primary fuse open These are also examples of what can cause a primary single phase condition.

Normal Condition M 1.4 A 1.4 A Under normal operation, the motor will draw 1.4 amps of current through each phase. 1.4 A 208V 1/3 HP Motor C F.L.A. = 1.4 Amperes

Single Phase Condition Assume one phase lost on the primary side of transformer. M 1.61 A (115%) 3.22 A (230%) If a phase were to open on the primary of the transformer, the motor would then draw 115% of the normal FLA in two of the phases and the other leg would draw 230% of the FLA. If this were to occur, what should take the system offline? The overload relay. Can the fuse protect against a single phasing condition? What about a circuit breaker sized at code maximum?(250% of FLA) (115%) 1.61 A 208V 1/3 HP Motor C F.L.A. = 1.4 Amperes

Secondary Single Phasing
Damaged Motor Starter Contact - One Pole Open Burned open overload relay (heater) Damaged switch or circuit breaker on the main, feeder, or branch circuit. Open fuse or open pole in breaker on main, feeder, or branch circuit. Open cable or bus on secondary of transformer terminals Secondary single phasing can occur in much the same way as the primary single phasing. A secondary single phase is the opening of one phase of the system on the secondary side of the transformer.

Open cable caused by overheated lug on secondary side-connection to service head. Open connection in wiring such as in motor junction box (caused by vibration) or any pull box Open winding in motor Open winding in one phase of transformer winding Here are more examples of secondary single phasing.

Normal Condition M 1.4 A Again under normal conditions, the motor draws the normal FLA. 208V 1/3 HP Motor C F.L.A. = 1.4 Amperes

Single Phase Condition Contacts on one phase are worn out resulting in an open circuit M 0 A 2.4 A (173%) If a secondary single phasing occurs, one leg to the motor would be disconnected. If the motor is already in operation, it may continue to operate on only two phases which will cause approximately 173% of the FLA to flow in the remaining two phases. What should protect the motor from this occurrence? The overload relay. The fuses or circuit breaker will not be able to open the circuit if sized in accordance with maximum levels. (173%) 2.4 A 208V 1/3 HP Motor C F.L.A. = 1.4 Amperes

1000 100 10 1 0.1 0.01 Time in Seconds Current in Amperes FRN-R-1-6/10 Motor Damage Curve Secondary Single Phasing However, what if the fuse is sized for overload protection? Can it protect from a secondary single phase condition? From the above picture you could say yes since the fuse curve is to the left of the motor damage curve.

1000 100 10 1 0.1 0.01 Time in Seconds Current in Amperes FRN-R-1-8/10 Motor Damage Curve Secondary Single Phasing Overload Relay What if the time-delay fuse is sized for backup overload protection? Again the main operating device in this condition should be the overload relay. But if the overload relay were to fail for some reason, will the fuse be able to protect the motor from the single phase condition?

What about short circuit protection for a motor circuit?

Current Source M A short circuit can occur in many different ways. The main thing to acknowledge with a short circuit is that the current will travel outside the normal path. In the example here a line to line fault occurred prior to entering the motor, causing a very large amount of current to travel through the remainder of the motor circuit. In the case of a short circuit, the fuse, circuit breaker, or MCP must be sized properly to be able to protect the Motor Circuit components from the disastrous effects of short circuit current. One thing to note is that the fuse, circuit breaker, or MCP cannot protect the motor from a short circuit. If a short circuit were to occur in the motor, the motor would already be damaged and most likely will need to be rewound or replaced. If a line to line fault were to occur as in the diagram, the short circuit current would not travel through the motor but actually through the short cut path back to the current source. You can however, use a properly sized overload device to reduce the chance of overload conditions breaking down the insulation in the motor causing a fault to occur. Short Circuit Condition

If the overcurrent protective devices are sized according to the maximums in NEC® , will the motor circuit components be protected from damage? The answer is no. The intent is to prevent fires outside the equipment or the energization of the equipment enclosures (to minimize the occurrence of electric shock.

TYPE 1 PROTECTION vs. TYPE 2 PROTECTION
Type 1 and Type 2 protection are distinct levels of motor circuit equipment protection, with Type 1 allowing considerable damage and Type 2 allowing “no damage” under short-circuit conditions.

TYPE 1 vs. TYPE 2 PROTECTION
What is Type 1 and Type 2 Protection? IEC Standard Type 1 Protection(Damage) UL 508 Listing Type 2 Protection(No Damage) Type 2 Tables from Manufacturer Type 1 and Type 2 protection evolved from Europe through the IEC standards.

“Requires that, under short-circuit conditions, the contactor or starter shall cause no danger to persons or installation and may not be suitable for further service without repair and replacement of parts.” Similar to UL 508 requirements Type 1 protection allows significant damage to the equipment. For all practical purposes, it requires that the door to the enclosure remains closed, the enclosure does not become energized and there is no fire outside of the enclosure. This is very similar to the way that UL tests a combination motor starter.

“Requires that, under short-circuit conditions, the contactor or starter shall cause no danger to persons or installation and shall be suitable for further use. The risk of contact welding is recognized, in which case the manufacturer shall indicate the measure to be taken as regards the maintenance of the equipment.” In Type 2 protection, No damage is allowed to either the contactor or overload relay. Light contact welding is permitted, but contacts must be easily separable. The only thing that is allowed to be replaced is the short circuit protective device. The equipment must be ready to be placed directly back into service after a fault. “No damage” Protection for NEMA and IEC motor starters can only be provided by very current-limiting devices.

Type 2 Protection Tables
To achieve Type 2 protection you must refer to manufacturers recommendations from tested combinations of OCPD and starters similar to what is shown.

Does NEC® require Type 2 protection? Does NEC® require Type 2 protection?

NEC® section : Circuit Impedance, Short- Circuit Current Ratings, and Other Characteristics. The overcurrent protective devices, the total impedance, the equipment short-circuit current ratings, and other characteristics of the circuit to be protected shall be selected and coordinated to permit the circuit- protective devices used to clear a fault to do so without extensive damage to the electrical equipment of the circuit……Listed equipment applied in accordance with their listing shall be considered to meet the requirements of this section. Yes and no. It depends upon your interpretation. The OCPD is required to open and clear a fault without allowing “extensive damage” to the equipment. But it also says that a listed product is applied in accordance with its listing it will meet the requirements of This means that a UL listed combination starter would be acceptable for if all faults were at least 4’ 10” from the controller. Of course, that guarantee can’t be made if a maintenance person is trouble-shooting an energized motor circuit. Most people, after witnessing a high short-circuit test of equipment that passed, would say that the results of such a fault would be extensive damage.

TYPE 2 PROTECTION Why Is Total Protection Important?
Maximum Safety To Personnel And Equipment Minimum Cost To Stay In Service Maximum Productivity From The Equipment Why Is Total Protection Important? Maximum Safety To Personnel And Equipment Minimum Cost To Stay In Service Maximum Productivity From The Equipment

Overload Protection Overload Relay Fuses for Backup Short Circuit Protection Fuse, Circuit Breaker, MCP Type 2 Protection(No Damage) Summary. Main focus is that Overload protection is provided by the overload relay. Fuses and Circuit breakers provide short-circuit protection. However, if using the proper type and proper size, fuses can also provide back-up overload protection to give two levels of overload protection. When it comes to short circuits, highly current limiting devices can be used to provide TYPE 2, no damage protection for motor starters. This is so that in the event of a short circuit, the equipment will not need to be replaced in order to proceed with operation. This will result in less cost for equipment expenses and less down time as a result of a short-circuit current.

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