Upsizing Equipment Grounding Conductor 250.122(B)

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I have a 400A, 480V Main Distribution Panel located on a platform near a river where power is feed from another location about 1200' away. (Getting the utility to provide a 3-phase service near the river would have taken forever). So, we have extended a feeder about 1200' away to this 400A panel; load on the panel is about 220A. Typically from a 400A breaker, I would run 500MCM with a #3 EGC. To compensate for voltage drop, I ran parallel 500MCM with #3EGC in two separate conduits. The inspector is telling me the EGC needs to be larger per 250.122(B). Now I understand what he is bringing up about proportionally increasing the EGC, but my thought behind this is 500MCM (500,000mils) and #3 (52,620 mils) so if I add a second 500MCM run (1,000,000mils of ungrounded conductor) and I include a 2nd EGC in the other conduit that would give me a total of 105,240 mils of EGC (total for the circuit). If I add a second 500MCM to compensate for voltage drop as I did, does the EGC in EACH conduit need to be upsized??? I think he is telling me I would need to proportionally increase the EGC in each (go with 1/0). I'm confused b/c they are separate conduits.
 
Nope parallel runs must have the appropriate size egc in each conduit. So if you need a 3/0 egc then it must be sized 3/0 in each parallel run.
 
The EGC in each conduit it required to be "full sized", meaning the size required due to the proportional increase. Looks like Dennis did the calculation.
 
You have two separate NEC requirements at play. One states that if you upsize the ungrounded conductors, you must also upsize the EGC. That is in 250.122(B), I believe (my code books are not handy). The other requirement is that if you run parallel conduits, there must be a full size EGC in each conduit. I don't recall the article number. These two, separate, requirements are what Dennis and Rob are talking about.
 
I thought with EGC, go by the rating of the OCD use T250.122 regardless of sizing of the wire..Yes, when running parallel full size EGC in each condiut.. Are you guying thinking of 250.66 sizing GEC, T250.66 700kcmils through 1100kcmils use 2/0 GEC??
 
squaredan said:
I thought with EGC, go by the rating of the OCD use T250.122 regardless of sizing of the wire..Yes, when running parallel full size EGC in each condiut.. Are you guying thinking of 250.66 sizing GEC, T250.66 700kcmils through 1100kcmils use 2/0 GEC??
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Dan if you oversize the wire that is needed for a branch circuit or feeder then you must size the egc proportionately regardless of the breaker. The breaker determines the size of the egc for a respective wire size. Change the wire size and you have to change the egc proportionately. Read 250.122(B)
 
SWEET! I like when i learn something.. So you size Proportionately, divide the Cir Mills to get the %... So #3 is 52620Cmils

52620/500,000= 0.10524 = 10.55% So two sets of 500kcmil = 1,000,000x .10524= 105240kcmils which is a 1/0 Chpt9 table 8 Is that correct?
 
squaredan said:
SWEET! I like when i learn something.. So you size Proportionately, divide the Cir Mills to get the %... So #3 is 52620Cmils

52620/500,000= 0.10524 = 10.55% So two sets of 500kcmil = 1,000,000x .10524= 105240kcmils which is a 1/0 Chpt9 table 8 Is that correct?
Click to expand...

Yep, you got it. :thumbsup:
 
Dennis Alwon said:
Dan if you oversize the wire that is needed for a branch circuit or feeder then you must size the egc proportionately regardless of the breaker. The breaker determines the size of the egc for a respective wire size. Change the wire size and you have to change the egc proportionately. Read 250.122(B)
Click to expand...

Keep in mind that this was a change in the 2008 code (I think it was 2008). Before that you only had to size the EGC to T250.122 and the overcurrent device. Both raceways of a parallel circuit still had to be full size EGC.
 
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