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Friday, June 2, 2017
Question:
Re: CQD answer published Friday, May 19, 2017 -Parallel Equipment Grounding Conductors
Good day Charlie,
I enjoy reading your Code Question of the Day every morning prior to performing my inspections for the day. In reference to your response to Greg McMurphy, dated 5/18/17, I respectfully disagree with your response and example. To clarify, 250.122(F) states where conductors are installed in parallel in multiple raceways the Equipment Grounding Conductor must be sized per Table 250.122, and installed in each conduit fully sized.
For example, I have a 500 amp Circuit Breaker, the EGC shall be sized to a #2 AWG, the phase conductors would be sized to 800 KCMIL. Instead of running 1 set of 800 KCMIL conductors, I chose to use 250 KCMIL conductors paralleled. Per 250.122(F) I’m still required to use #2 AWG EGC in both conduits.
The example you gave of adding the total sum of both parallel conductors is only used when applying the provisions of Table 250.66, which is used to calculate the size of the Grounding Electrode Conductor.
If I were to increase the phase conductors due to voltage drop, then per 250.122(B) I would need to increase the Equipment Grounding Conductor sized proportionately to the phase conductors.
Using the same scenario for the 500 amp Circuit Breaker.
I increased the parallel conductors from 250 KCMIL to 300 KCMIL, this would be an increase of 120 %. Per Table 8 of Chapter 9, a #2AWG conductor has a circular mils of 66360 multiplied by 120% = 79,632 circular mils, the conductor size that correlates closest to that sum would be #1 AWG. I would then have 300 KCMIL phase conductors and a #1 AWG EGC paralleled.
Thank you, Mike Cross
A
Answer:
Hey Mike thanks for your question and we are glad you enjoy CQD. The example you gave is correct, equipment grounding conductors (EGC) are sized based on the overcurrent device, whether the conductors are in a single raceway or in multiple raceways. For multiple raceways you need an EGC in each raceway but the words "fully sized" are not part of the rule 1n 250.122(F).
What I meant by "adding the parallel conductors together" was just to help explain what the ungrounded conductor size is in 250.122(A), it is not just the ones in each raceway and is not used for sizing the EGCs.