The Basics What is Electrical Current? Answer: Electron Flow

Field Rep Training Modules Electrical Insulated Conductors Dec 10, 2019

The Basics What is Electrical Current? Answer: Electron Flow
Electrical current is the flow of electrons in a conductor. Current is produced when an excited electron from one atom collides with an electron from another atom. This action displaces the electron from its orbit around the nucleus. This electron flow is known as electricity.

The Basics How is Electricity Produced? Answer: 6 ways
1: Magnetism 2: Chemical 3: Pressure 4: Heat 5: Friction 6: Light Magnetism is the most common way to generate electricity. The movement of a wire in a magnetic field generates electricity in the wire. Ie. Motors and Generators.

DC Resistance Electron flow through a conductor connected to a direct current source is subject to some amount of ohmic resistance, depending on the conductor material, length, and diameter. As the frequency increases, the skin effect increases. At low frequencies, such as 60 Hz, the skin effect has very little effect on the resistance of the conductor and generally is not taken into consideration when computing the size wire needed for a particular circuit. Eddy currents are created through a process called electromagnetic induction. When alternating current is applied to the conductor, such as copper wire, a magnetic field develops in and around the conductor. This magnetic field expands as the alternating current rises to maximum and collapses as the current is reduced to zero. If another electrical conductor is brought into the close proximity to this changing magnetic field, current will be induced in this second conductor. Eddy currents are induced electrical currents that flow in a circular path. They get their name from “eddies” that are formed when a liquid or gas flows in a circular path around obstacles when conditions are right.

AC Resistance In a conductor connected to an alternating current source, the resistance of the conductor to the flow of current is slightly higher because AC causes the electrons to be repelled toward the outer surface of the conductor. This phenomenon is called the “skin effect” The “skin effect” is proportional to frequency. At 60 Hz, skin effect is not a factor in determining wire size for 600 V applications. As the frequency increases, the skin effect increases. At low frequencies, such as 60 Hz, the skin effect has very little effect on the resistance of the conductor and generally is not taken into consideration when computing the size wire needed for a particular circuit. Eddy currents are created through a process called electromagnetic induction. When alternating current is applied to the conductor, such as copper wire, a magnetic field develops in and around the conductor. This magnetic field expands as the alternating current rises to maximum and collapses as the current is reduced to zero. If another electrical conductor is brought into the close proximity to this changing magnetic field, current will be induced in this second conductor. Eddy currents are induced electrical currents that flow in a circular path. They get their name from “eddies” that are formed when a liquid or gas flows in a circular path around obstacles when conditions are right.

Conductor Materials According to Clause of the NEC, allowable conductor materials for applications up to 2000 V are: Copper Aluminum Copper-clad aluminum Aluminum conductors for building wire are most commonly AA-8000, but may be AA-1350 for some applications such as USE-2.

A metal formed by the combination of two or more metals
Alloy A metal formed by the combination of two or more metals Copper is not typically alloyed. Aluminum may be alloyed to produce specific electrical, mechanical and physical properties. 1350 AA 8000 series The combination of metals into an alloy can drastically change the electrical, mechanical and physical properties of an element depending on the addition of various other elements. Typically, alloyed conductors are engineered and designed to produce specific electrical, mechanical and physical properties. The initial strength of alloys in this group depends on the hardening effect of elements such as manganese, silicon, iron, and magnesium, singly or in various combinations. These alloys are work-hardenable and further strengthening is made possible by various degrees of cold working. Alloys containing appreciable amounts of magnesium are usually given a final elevated-temperature treatment called “stabilizing” to ensure stability of properties. Initial strength of these alloys is enhanced by the addition of alloying elements such as copper, silicon, zinc, silicon, and magnesium. Since these elements singly or in various combinations show increasing solid solubility in aluminum with increasing temperature, it is possible to subject them to thermal treatments that will impart pronounced strengthening. Annealing is a process that consists of heating the metal to or above re-crystallization temperature for a period of time to allow the new molecular structure to stabilize.

Solid Conductors Smaller wire sizes (14, 12 and 10 AWG) are typically solid conductors, but may be stranded. The NEC allows aluminum conductors 12 AWG and above for general wiring, 14 AWG copper conductors.

Stranded Conductors What are they?
Conductors composed of a group of wires or of any combination of groups of wires. Stranded conductors can be unilay or reverse-lay stranded (or other geometric configuration), and can be concentric, compressed, rope-lay, bunch or compact stranded. Conductors may be either lengths of single wires or a stranded group of smaller wires arranged in some regular manner. In either case, the cross-sectional area of all conducting wires determine the AWG or circular mil size of the assembled conductor.

Stranded Conductors Why Use Them?
Practicality in Handling Flexibility during installation Connectability/Terminations Conductors may be either lengths of single wires or a stranded group of smaller wires arranged in some regular manner. In either case, the cross-sectional area of all conducting wires determine the AWG or circular mil size of the assembled conductor.

Stranded Conductors Designations
ASTM International* categorizes conductor stranding in classes: B, C, D, etc. Increased flexibility of stranded conductors is signified by progression in letter designations. (e.g. Class M is more flexible than Class B) Table 8 of NEC® Chapter 9 includes conductor properties for solid and Class B stranded conductors. Some stranded conductors conform to ASTM standards for single-input wire, which may have a different number of strands than classical stranding methods. *Formerly known as American Society for Testing and Materials ASTM B (2005) defines SIW as "Single Input Wire Construction- A stranded conductor design methodology that varies the number of wires within a range of conductor sizes in order to permit that range of conductor sizes to be constructed from a single wire size."

Stranding Types Concentric Stranding
Constructed with a central wire surrounded by one or more layers of helically wound strands in a fixed round geometric arrangement. Unilay Stranding and Unidirectional Stranding Electrical Conductivity: Slightly lower than true concentric; higher conductivity than bunched for 18 gauge and finer, lower for 16 gauge through 10 gauge. Diameter Control: Best in diameter control and smaller diameters. Weight Control: Best weight control and lowest weight for equivalent conductivity. Flexibility: Higher flexibility than true concentric or bunched with fewer strands. Crimp Termination: Concentric strandings are best for crimping due to less "give". General: Excellent diameter control and very smooth surface; used for thin wall insulations, both extruded and tape wrapped.

Stranding Types Bunch Stranding
A group of wires twisted together in the same direction with no pre- determined pattern Bunched Stranding Electrical Conductivity: Designed to have same conductivity as equivalent solid gauges. Diameter Control: Poor diameter control because of non-geometric configuration. Weight Control: Poor weight control but usually not important for bunched. Flexibility: Dependant upon number if strands; more strands equals better flexibility. Crimp Termination: Poor for quality crimp terminations, usually soldered. General: Generally used for lower temperature, heavier insulation thickness.

Stranding Types Rope Stranding
Shown as concentric rope stranded construction with concentric-stranded component wires Rope Stranding Electrical Conductivity: Generally designed to have same conductivity as equivalent solid gauges except 19 x 7 end construction, which is greater. Diameter Control: Dependent upon configuration; generally more strands means less control. Weight Control: Dependent upon configuration; generally more strands means less control. Flexibility: Best flexibility due to greater number of strands. Crimp Termination: Generally good for crimping because of mass, depending upon configuration. General: Can be used with any insulation, depending upon configuration.

Stranding Types Compressed Stranding
A concentric stranded conductor drawn through a forming die (to about 97% of its original diameter, but with the same volume of metal). Concentric StrandingElectrical Conductivity: Slightly higher than unilay; same comparison with bunched as unilay. Diameter Control: Better than bunched or ropes. Weight Control: Good weight control. Flexibility: Least flexibility when compared to other types of stranding with the same number of strands. Crimp Termination: Concentric strandings are best for crimping due to less "give." General: Very good diameter control and smooth surface; used for thin wall insulations, both extruded and tape wrapped.

Stranding Types Compact Stranding
A concentric stranded conductor drawn through a series of forming dies (to about 90% of its original diameter, but with the same volume of metal). Concentric Stranding Electrical Conductivity: Slightly higher than unilay; same comparison with bunched as unilay. Diameter Control: Better than bunched or ropes. Weight Control: Good weight control. Flexibility: Least flexibility when compared to other types of stranding with the same number of strands. Crimp Termination: Concentric strandings are best for crimping due to less "give." General: Very good diameter control and smooth surface; used for thin wall insulations, both extruded and tape wrapped.

Stranding Types Compressed and Compact Stranding Benefits
Smoother conductor interface for stripping Normally used for larger sizes Helps reduce the overall cable diameter Helpful in increasing the number of conductors in conduit Concentric and Compact Stranding Electrical Conductivity: Slightly higher than unilay; same comparison with bunched as unilay. Diameter Control: Better than bunched or ropes. Weight Control: Good weight control. Flexibility: Least flexibility when compared to other types of stranding with the same number of strands. Crimp Termination: Concentric strandings are best for crimping due to less "give." General: Very good diameter control and smooth surface; used for thin wall insulations, both extruded and tape wrapped.

NEC Clause 110.14 Marking of Stranding
Connectors and terminal for conductors more finely stranded than class B and Class C shall be identified for the specific conductor class These specific conductor classes (other than Class B and Class C) would be part of the conductor marking

Insulation Materials Materials include: Thermoplastic compounds
Thermoset compounds See NEC© Table (A) Thermoplastic - a material that repeatedly can be softened by heating and hardened by cooling through a temperature range characteristic of the material, and that in the softened state can be shaped through the application of force. Thermoset - an insulating or jacketing polymeric material which, when cross-linked, will not flow on subsequent heating.

Commercial/Industrial Conductors
XHHW-2 USE-2/RHH/RHW-2 Typically single conductors are not used in residential wiring applications

RHW vs. XHHW RHW requires a thicker insulation
RHW and XHHW are both normally manufactured with a “-2” rating, allowing use in 90 degrees C, wet or dry RHW is often multi-rated to include insulation types RHH and USE (e.g. USE- 2/RHH/RHW-2)

Commercial/Industrial Conductors
THHN / THWN-2 PVC Typically single conductor THHN is not used in residential wiring applications either. THHN is often used in combination with THWN-2 to allow the conductors to be used in wet locations. Nylon

Applications for XHHW or THWN
Service entrance – either in cable or conduit Feeders – either in cable or conduit Branch circuits – either in cable or conduit Wet or dry locations Aboveground or underground in cable or conduit

Sunlight Resistance Per NEC® (D), insulated conductors or cables used where exposed to direct rays of the sun must be listed, or listed and marked, as being sunlight resistant. Suitability for dry, dry/damp and wet locations is identified by the conductor and cable Type designation, whereas suitability for exposure to direct sunlight is indicated by the SUN RES marking on the completed cable.

“W” (Wet) Rated Conductors
“W” as part of the insulated conductor Type designation indicates that it may be used in a wet location. Insulated conductors with a “–2” in their Type designation are 90°C rated wet or dry. Refer to NEC Table (A) for conductor Type designations and temperature ratings.

Ampacities of insulated conductors or cables
Ampacities can be found in tables in NEC Article 310 or under engineering supervision, derived from the Neher-McGrath formula in NEC (C) Under engineering supervision, conductor ampacities shall be permitted to be calculated by the following equation: where: Tc = conductor temperature in degrees Celsius (°C) Ta = ambient temperature in degrees Celsius (°C) Rdc = dc resistance of 305 mm (1 ft) of conductor in micro-ohms at temperature, Tc Yc = component ac resistance resulting from skin effect and proximity effect Rca = effective thermal resistance between conductor and surrounding ambient The NEC tables are built around 30 degrees C earth ambient temperature, 100% load factor, an earth thermal resistivity of 90, and 60, 75, and 90 degrees C rated conductors and several other limiting factors that could vary given a particular location and environment. In the plethora of cases where conditions do not conform to the restrictions set forth in the NEC tables, the Neher-McGrath formula can be used to derive the ampacity of conductors.

Correction Factors from Table 310.15(B)(2)(a)
Conductor ampacity from the NEC Tables are based on an ambient of 30ºC. Ambient temperature correction factors are important because exposing conductors to ambient temperatures are higher than 30ºC may cause insulation failure. There may be additional de-rating factors not covered in this presentation. This slide addresses only correction factors from Table (B)(2)(a), and is not meant to be an in-depth discussion of this issue.

Cable Design Selection of power cable for a particular circuit or feeder should be based on the following considerations, as applicable: Electrical Thermal Mechanical Chemical Flame Resistance Limited Smoke Acid Gas Emission Electrical - dictates conductor size, type and thickness of insulation, correct materials for low- and medium-voltage designs, considerations of dielectric strength, insulation resistance, specific inductive capacitance, and power factor. Thermal - compatibility with ambient and overload conditions, expansion, and thermal resistance. Mechanical - involves toughness and flexibility, consideration of jacketing or armoring, and resistance to impact, crushing, abrasion, and moisture. Chemical - stability of materials on exposure to oils, flame, ozone, sunlight, acids and alkalies. Flame Resistance - Cables installed in cable tray must be listed as flame retardant and marked for installation in cable tray. The marking may be “Type TC, “TC”, “for use in cable trays”, or “for CT use”, depending on the voltage and construction. Low Smoke - The NEC authorizes the addition of the suffix “ST1” to the cable marking on any cable construction that is flame retardant and has limited smoke characteristics. While the NEC does not specifically require the use of “ST1” construction in any area, this requirement might be considered for occupancies with large populations or high-rise occupancies. Toxicity - All electrical wire and cable installed or terminated in any building in the State of New York after December 16, 1987 must have the toxicity level and certain other data for the product on file with the New York Secretary of State.

Proper Connection Methods
The following slides will describe the proper method to terminate conductors on compression and mechanical connectors Thanks to the NEMA Electrical Connector Section for providing slides on proper connection methods.

Connector Installation Guide For Compression Connectors
Determine Proper Connector For Cable Conductor size and CU = Copper conductors only Conductor size and “AL9” = Aluminum conductors only Conductor size and “AL9CU” = Aluminum or Copper conductors Match size and type of conductor to proper lug Note: Consult manufacturers instructions on whether fine stranded conductors or welding cable conductor types may be used.

Marking Information on Connectors: Manufacturer Wire Size Wire material- CU, AL, or AL9CU (indicates Dual Rating and 90° C) Optional Crimp Indicator Bands Listing Information

2. Strip and Properly Prepare Cable Strip insulation carefully to avoid nicking strands. Strip to proper length so conductor can be fully inserted. Refer to manufacturers instructions for strip length. Most connectors are suitable for one conductor. Never install more than one conductor unless specifically allowed by the manufacturer’s instructions.

Strip and Properly Prepare Cable (Continued) Brush the stripped portion of the conductor to remove oxide film using a stainless steel wire brush. Apply oxide inhibitor compound if recommended by the connector manufacturer. Do not remove pre-filled inhibitor from the barrel.

3. Select proper installing die tool Always refer to the connector manufacturer’s instructions for the proper compression die that is intended for the connector. Manufacturers may use colored bands or dots that correspond to color markings on dies. Manufacturers may use die code number marked or stamped on the connector. Knurls may be used in place of colored bands.

Locate tool with correct die in proper position on connector and activate tool Connectors that are banded with colored stripes to indicate number and location of each crimp. Connectors may also be marked with the die code number at each compression location. Follow manufacturers instructions whether to crimp on the colored bands or between the colored bands.

4. Continued…. When crimped, the die code number or other marking will be embossed on connector for easy inspection to determine if correct die and connector combination were used.

4a. Die-less Tools Select proper installing die-less tool * Crimp as directed by the manufacturer’s instructions. * Advanced tools are now available with RF sensing technology allowing terminals to provide compression requirements directly to the tools.

5. Connector Securement Use a 2-hole connector if there is a concern for twisting the connection.

Connector Installation Guide For Mechanical Connectors
Connector Types Double Conductor Lug Single Conductor Lug Overhead Transformer Copper Single Conductor Lug Stud Type Transformer Double Conductor Lug, NEMA Pad

Marking Information on Connectors: Manufacturer’s name or Symbol Wire Size or range Wire material- CU, AL, or Both Temperature Rating if applicable AL9CU Shows Dual Rating (Al & Cu) and 90°C UL and/or CSA if it is a listed connector Caution: Fine-stranded wires may only be used with connectors that are specifically listed and marked for use with fine-stranded wires. This applies to both set-screw and crimp-on connectors.

Unlike Compression connectors, mechanical connectors typically take a range of conductors. It is important to check that the cable falls within the cable range listed on the connector. If the connector is intended to be used on a bus, pad or equipment, mount the connector and tighten the mounting hardware per the manufacturer’s specifications.

6.Strip and Properly Prepare Cable Strip insulation carefully to avoid nicking strands Strip to proper length so conductors can be fully inserted Refer to manufacturers instructions for strip length Brush the stripped portion of the conductor to remove oxide film with a stainless steel wire brush. Apply oxide inhibitor compound if recommended by the connector manufacturer.

Insert the conductor(s) and tighten all set screws per the manufacturer’s recommendations. Do not retighten after properly torqued. Most connectors are suitable for one conductor. Never install more than one conductor unless specifically allowed by the manufacturers instructions. Use the mounting bolt size as recommended by the manufacturer.

Connector Installation Guide Connector Rating Marking
Marking Material Temp Rating AL 9 Aluminum °C AL9CU CU9AL Aluminum/Copper °C AL7 Aluminum °C AL7CU CU7AL Aluminum/Copper °C CU9AL

Good Connections Follow manufacturers instructions Torque requirement
Cleaning/wire brushing contact surfaces Use of hardware (nuts, bolts, washers) Oxide inhibitors Strip length

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The Basics What is Electrical Current? Answer: Electron Flow

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