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Table 310.15(B)(16) Parallel Conductor and  Voltage Drop Calculator
by
electrician2.com

This calculator finds the conductor ampacity, maximum overcurrent protective device size and Voltage Drop for branch circuits and feeders using Table 310.15(B)(16 )per Section 240.4(B), and (D) and otlated sections of the NEC.

Written by Gerald C Newton  December 2006.  Updated to 2011 NEC 04/03/2011

Select Material

Ambient
Temperature C
Number Current Carrying Conductors in Raceway or Cable or bundled  see Note 2

Select Conductor Size

Select number
 of conductors in parallel

Special Condition

Select Conductor Insulation Temperature see Note 3 Select Termination Temperature C. Circuit is bundled or in raceway 24 inches or less in length

Yes

 
   

No

 

CLICK BUTTON FOR OUTPUTS BELOW

Parallel Conductors Derated ampacity

Parallel OCPD Maximum Size

Parallel Equip Grnding Cond.  Size
see Note 6

Single Conductor Data

Single Conductor Derated ampacity

Single OCPD Maximum Size

Single Equip Grnding Cond.  Size

Single Maximum Continuous Load (amperes)

   

Data


Conductor ampacity

Terminal
Ampacity

 
Ambient
Correction
Factor


 

Conductor circular mil area



 
Conductor Derating Factor for more than three current carrying conductors
    Total Derating Factor

Voltage Drop for above Parallel Conductors
(For parallel conductors the load is the maximum OCPD divided by number of conductors.)

Select voltage and phase, Enter Distance, Then Click Calculate Button
(This calculator uses k=12.9 for copper or k=21.2 for aluminum)
Select Voltage
and Phase

Enter Distance in
feet from supply to load (one way)

Input from above program: (The Load can be changed by using the keyboard)
Material conductor Size CMA of conductor Load k (circular mil-ohm ft.
Voltage drop
Voltage at load end of circuit
Per Cent voltage drop
Equipment Grounding Conductor Size
(proportionally increased- per 250.122 (A)and (B))

Notes:
1.  240.4(B) Devices Rated 800 Amperes or Less. The next higher standard overcurrent device rating (above the ampacity of the conductors being protected) shall be permitted to be used, provided all of the following conditions are met: (1) The conductors being protected are not part of a multioutlet branch circuit supplying receptacles for cord and- plug-connected portable loads.  Also see Table 210.24 and Section 210.23.
240.4(C) Devices Rated Over 800 Amperes. Where the overcurrent device is rated over 800 amperes, the ampacity of the conductors it protects shall be equal to or greater than the rating of the overcurrent device defined in 240.6.
2. 
Neutral Conductor. (a) A neutral conductor that carries only the unbalanced current from other conductors of the same circuit shall not be required to be counted as a current carrying conductor.
(b) In a 3-wire circuit consisting of two phase wires and the neutral of a 4-wire, 3-phase, wye-connected system, a common conductor carries approximately the same current as the line-to-neutral load currents of the other conductors and shall be counted as a current carrying conductor.
(c) On a 4-wire, 3-phase wye circuit where the major portion (over 50 per cent) of the load consists of nonlinear loads such as electric discharge lighting and computer loads, harmonic currents are present in the neutral conductor and the neutral shall be considered a current carrying conductor.
(d) Each current-carrying conductor of a paralleled set of conductors shall be counted as a current carrying conductor.
3.  Termination provisions of equipment for circuits rated 100 amperes or less, or marked for 14 AWG through 1 AWG conductors, shall be used only for one of the following:
(1) Conductors rated 60C (140F).
(2) Conductors with higher temperature ratings, provided the ampacity of such conductors is determined based on the 60C (140F) ampacity of the conductor size used.
(3) Conductors with higher temperature ratings if the equipment is listed and identified for use with such conductors.
(4) For motors marked with design letters B, C, or D, conductors having an insulation rating of 75C (167F) or higher shall be permitted to be used, provided the ampacity of such conductors does not exceed the 75C (167F) ampacity.
Termination provisions of equipment for circuits rated over 100 amperes, or marked for conductors larger than 1 AWG, shall be used only for one of the following:
(1) Conductors rated 75C (167F)
(2) Conductors with higher temperature ratings, provided the ampacity of such conductors does not exceed the 75C (167F) ampacity of the conductor size used, or up to their ampacity if the equipment is listed and identified for use with such conductors.
Author's Note:  In general most terminals are rated for 75 degrees C.  Conductors with 90 degree C insulations can be used on these terminals provided they are not used at an ampacity higher than the 75 degree C. ampacity.   However, the 90 degree insulation ampacity can be used for derating purposes.    For example a No. 12 AWG copper 90 degree C. THHN rated at 30 amperes can be used in a raceway with up to 9 current carrying conductors on a 20 ampere circuit breaker since the  derated  ampacity is 0.7 x 30 = 21 amperes.
75 degree terminations may be stamped as AL7CU.
4Conductors in Parallel. Aluminum, copper-clad aluminum, or copper conductors of size 1/0 AWG and larger, comprising each phase, polarity, neutral, or grounded circuit conductor, shall be permitted to be connectedin parallel (electrically joined at both ends).
5.  Where parallel conductors are run in separate raceways or cables, the raceways or cables shall have the same physical characteristics.  Where conductors are in separate raceways or cables, the same number of conductors shall be used in each raceway or cable. Conductors of one phase, polarity, neutral, or grounded circuit conductor shall not be required to have the same physical characteristics as those of another phase, polarity, neutral, or grounded circuit conductor to achieve balance.
6.  Where conductors are run in parallel in multiple raceways or cables as permitted in NEC Section 310.4, the equipment grounding conductors, where used, shall be run in parallel in each raceway or cable.
The size of the equipment grounding conductor shall be based on 1 or 2 below:

1.  (This calculator uses this method.) Each parallel equipment grounding conductor shall be sized  on the basis of the ampere rating of the overcurrent device protecting the circuit conductors in the raceway or cable in accordance with Table 250.122.

2.  Where ground-fault protection of equipment is installed, each parallel equipment grounding conductor in a multiconductor cable shall be permitted to be sized in accordance with Table 250.122 on the basis of the trip rating of the ground-fault protection where conditions given in NEC Section 250.122 are met.


Example

Given:

Find the combination of 350 kcmil copper XHHW-2 conductors, BARE equipment grounding conductor, and size of conduit at 40 per cent fill to supply a 1000 ampere load.  Voltage drop is limited to 2 per cent.  Terminals are rated at 75 degree C.
The circuit is 480/277 volts three phase in PVC schedule 80 conduit 100 feet long.  The majority of the load is nonlinear.

Using the T310.16 Parallel Calculator:  Since the majority of the load is nonlinear there are a minimum of 4 current carrying conductors in each raceway,  A-ph, B-ph, C-ph, and the neutral.  4ea  350 kcmil are permitted on a 1000 ampere circuit breaker.  The equipment ground is 2/0 AWG.  The voltage drop for 100 feet is 0.3 per cent.

Using the raceway fill calculator the size of conduit is:  3 inch schedule 80 PVC.

The installation would consist of 4 each 3 inch raceways with 4 each 350 kcmil conductors and a bare 2/0 equipment grounding conductor in each raceway.  Each raceway would have A-phase, B-phase, C-phase, and a Neutral 350 kcmil XHHW-2 copper conductor and a 2/0 AWG bare copper equipment grounding conductor.

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