2 circuits via one 4/c cable

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mikelagoda

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Hello,

Can one 4/c, #6 /w #8 GND Mc-HL cable be used for two branch circuits (15A each; power for 2 heat trace cables; cable is upsized due to the voltage drop)?

It doesn't look right but I couldn't find anything in the NEC that does not allow such configuration.

Please help.

Thanks,

Mike
 
Both circuit breakers are 40A, 2-pole (same 208Y/120V heat trace panelboard) and each of the circuits has it is own overcurrent protection (CT + contactor).

Is sharing equipment grounding conductor for 2 circuits acceptable per NEC?
 
Unfortunately, no. And this is really stupid. Since the circuit would normally be 15 Amps with #14 conductors and #14 ground and the rule that you have to proportionally upsize the EGC when upsizing the current carrying conductors for voltage drop, the #8 EGC is not big enough for the #6 current carrying conductors. See 250.122(B) (I'm still in 2005).

Sorry. I said it was stupid.

Mark
 
Is sharing equipment grounding conductor for 2 circuits acceptable per NEC?
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Yes, see 250.122(C)

Unfortunately, no. And this is really stupid. Since the circuit would normally be 15 Amps with #14 conductors and #14 ground and the rule that you have to proportionally upsize the EGC when upsizing the current carrying conductors for voltage drop, the #8 EGC is not big enough for the #6 current carrying conductors. See 250.122(B) (I'm still in 2005).

Sorry. I said it was stupid.
Click to expand...

I agree that if the ungrounded conductors were upsized to a #6 from a #14 then a #8 EGC would not work due to 250.122(B). But you can use a single EGC for multiple circuits run in the same raceway or cable.

Chris
 
mikelagoda said:
Both circuit breakers are 40A, 2-pole (same 208Y/120V heat trace panelboard) and each of the circuits has it is own overcurrent protection (CT + contactor).

Is sharing equipment grounding conductor for 2 circuits acceptable per NEC?
Click to expand...

This is an odd arrangement. You can just add a 4 circuit subpanel at the end of the mc and feed the 2 circuits with #14 and a 15 amp breaker. o need to upsize the egc if you install a 60 amp breaker to the panel.
 
I believe they made the vd voltage drop change in the 96 code, we shouldnt forget that one.
 
djd said:
I believe they made the vd voltage drop change in the 96 code, we shouldnt forget that one.
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Yes, but in the 2002 NEC 250.122(B) the term voltage drop was removed from that section so you now have a requirement to upsize the EGC anytime the ungrounded conductors are upsized not just for voltage drop.

Chris
 
I already said it was stupid. A #8 ground is OK on a 60A circuit with #6 wires, but not a 15A circuit with #6 wires and a #8 ground. Where is the new proposal when you need one.

Mark
 
mikelagoda said:
Both circuit breakers are 40A, 2-pole (same 208Y/120V heat trace panelboard) and each of the circuits has it is own overcurrent protection (CT + contactor).

Is sharing equipment grounding conductor for 2 circuits acceptable per NEC?
Click to expand...

Do these heat trace units come equipped with 15 or 20 amp plugs?
 
Since the source is a 3ph panel, couldn't a 3-conductor cable be used, the two circuits sharing one conductor, and fed from a 3-pole breaker? The two heaters could be connected sorta like an open Delta.
 
Thank you all for providing post haste input.

The EGC conductor size is not an issue in this particular case as the metalic sheath of the MC-HL cable will be also used.

Thanks,

Mike
 
mikelagoda said:
Hello,

Can one 4/c, #6 /w #8 GND Mc-HL cable be used for two branch circuits (15A each; power for 2 heat trace cables; cable is upsized due to the voltage drop)?

It doesn't look right but I couldn't find anything in the NEC that does not allow such configuration.

Please help.

Thanks,

Mike
Click to expand...

Yes.

The grounding upsizing is incorrectly argued. The ground faults will be out of phase with each other, should they occur simultaneously.:rolleyes:
 
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