Cable Data

Five different cable types can be modeled. Cable type is used in determining the impedance of the conductor.

• 1/C - One conductor. Three separate conductors are used for a circuit, one each for A phase, B phase and C phase.
• 3/C - Three conductor. This is the same as three separate conductors, except that the conductors are encased with an insulated overall outer jacket effectively forming one cable. The cable may or may not have an interstitial ground wire.
• IAA - Interlocked armor aluminum. This is the same as the three conductor cable except that the outer jacket is made of aluminum instead of protective insulation. IAA is a generic term for describing any type of aluminum jacket including continuous sheath products such as Okonite CLX.
• IAS - Interlocked armor steel. This is the same as IAA except that the outer jacket is made of steel instead of aluminum.
• MAC - Messenger aerial cable. Messenger aerial cable is three separate conductors bundled together with a messenger cable easy hanging from poles. Because the conductors are held in a triangular fashion with the bundling, the impedance of this configuration is the same as for the 3/C cable.

Note: For Teck cables, select the CSA unit. For single conductor Teck, select 1/C and for 3-conductor Teck, select IAA for aluminum armor or IAS for steel armor. Look for Teck or Teck-90 in the Insulation type.

US Low Voltage Insulation (1000 volts or less):

• EPR - Ethylene Propylene Rubber.
• PVC - Polyvinyl chloride.
• RH - Heat Resistant Rubber, 75^oC.
• RHH - Heat Resistant Rubber.
• RHW - Moisture and Heat Resistant Rubber. This is the 480 volt equivalent of EPR.
• THHN - Heat Resistant Thermoplastic.
• THWN - Moisture and Heat Resistant Thermoplastic.
• THW - Moisture and Heat Resistant Thermoplastic.
• TW - Thermoplastic insulated moisture resistant cable.
• XHHW - Moisture and Heat Resistant Crosslinked Synthetic Polymer. This is the 480 volt equivalent of XLPE.

US High Voltage Insulation (Over 1000 volts):

• XLPE - Crosslinked Polyethylene.
• XLPE-133% - Crosslinked Polyethylene with 133% insulation.
• XLPE-NJ - Non-Jacketed Crosslinked Polyethylene.
• XLPE-NJ-133% - Non-Jacketed Crosslinked Polyethylene with 133% insulation.
• XLPES - Shielded Crosslinked Polyethylene.
• XLPES-133% - Shielded Crosslinked Polyethylene with 133% insulation.
• EPR - Ethylene Propylene Rubber.
• EPR-133% - Ethylene Propylene Rubber with 133% insulation.
• EPR-NJ - Non-Jacketed Ethylene Propylene Rubber.
• EPR-NJ-133% - Non-Jacketed Ethylene Propylene Rubber with 133% insulation.
• EPRS - Shielded Ethylene Propylene Rubber.
• EPRS-133% - Shielded Ethylene Propylene Rubber.
• PILC - Paper Insulated Lead Sheath.
• PILC-133% - Paper Insulated Lead Sheath with 133% insulation.

Medium in which the conductor is supported or run (conduit, cable tray, air, or direct buried). If none is selected, the cable ampacity defaults to 10A.

Note: For buried conduits, you can apply the derating for ampacity in the Duct Config field on the Specifications 2 tab.

Temperature of the loaded conductor. This can be varied from 25C to 250C depending on the type of study being performed. Cable temperature is used in determining the resistance of the conductor. The resistance increases with the conductor temperature.

Note: This is not the ambient air temperature or the ground temperature.

Distance between the outside insulation or jacket edges of adjacent phase conductors. This will affect the reactance calculations. All three spacings are modeled as the same or as a GMD equivalent.

Note: This is not the center to center distance. See figure below.

Figure 4: Conductor Spacing: Zero Spacing (Left) and With Spacing (Right)

Ampacity Derating

This field allows for cable ampacity derating based on the number of conductors in the conduit, tray or duct. Select from D-1, D-2, and so on, which correspond to NEC Detail 1, NEC Detail 2, and so on, of the National Electric Code. If this field is left blank, a 1.0 multiplier is assumed for the ampacity calculations. The rating factors are stored in the standard device library and can be customized if needed. If you need to derate cables based on number of conductors in the conduit or tray, you can add to the library.

Figure 5: Cable Derating in the Standard Device Library

Figure 6: 11.5” X 11.5” Electrical duct bank. One electrical duct

Figure 7: 19” X 19” Electrical duct bank. Three electrical ducts

For a complete listing of duct configurations, please see article 310 in the National Electric Code.

Ground conductor type (none, interstitial, separate, or as part of a group of conductors). This choice has an effect on the zero sequence impedance calculation. See Reference 1 for more information on ground impedance calculations.

None: No ground conductor.

Interstitial: The ground wires in a three conductor cable (or IAA, IAS, CLX, TEC). Typically there are three bare ground wires spaced evenly between the phase conductors.

Figure 9: Interstitial Ground

Separate: A separate ground conductor in a conduit for a specific circuit.

Figure 10: Separate Ground

Group: A ground conductor in a duct bank or tray that is used for multiple circuits.

Ground conductor size. This value is for reference only and does not affect analysis.

Note: The size of ground wire may not have a direct influence on the effective zero sequence resistance (R0) and reactance (X0). Refer to Kaufmann’s paper on grounding. For steel conduits, ground currents flow through the conduit close to the outer surface because of skin effect.

EasyPower offers two methods for calculating R_H:

• Resistance varying with a power of the harmonic (R-EXP):

R_H = R_Fund * H ^R-EXP

• Resistance varying with a percent eddy current factor (%ECF):

R_H = R_Fund * (1+ECF*H²)/(1+ECF)

EasyPower defaults all skin effect correction to R-EXP and a value of 0.5.