EGC size

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codequestion

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Just want to verify regards to NEC 250.122 (B) and (f). I have 400 amps feeder circuit breaker feeding panel 465 feet away. Normally 500 kcmil + #3 gnd would be good. However due to voltage drop the size is increased to 2 sets of 500 kcmil but not sure of EGC would be upgraded.

If upgraded then it would be 2x 52620= 105240 which is 1/0. So it would be 1/0 awg each or full size awg each per 250.122 (f) since parallel.
Do I have to upgrade EGC for voltage drop in my situation? If so then 1/0 awg or full size each per 250.122 (f)? What would be full size?

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codequestion said:
Just want to verify regards to NEC 250.122 (B) and (f). I have 400 amps feeder circuit breaker feeding panel 465 feet away. Normally 500 kcmil + #3 gnd would be good. However due to voltage drop the size is increased to 2 sets of 500 kcmil but not sure of EGC would be upgraded.

If upgraded then it would be 2x 52620= 105240 which is 1/0. So it would be 1/0 awg each or full size awg each per 250.122 (f) since parallel.
Do I have to upgrade EGC for voltage drop in my situation? If so then 1/0 awg or full size each per 250.122 (f)? What would be full size?

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Yes. You must increase the size of the EGC proportional to the increase in size of the ungrounded conductors, but the EGC never needs to be larger than any phase or grounded conductor.

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Since you have doubled the "size" of the phase conductors you need to double the size of the EGC in each raceway.
 
ActionDave said:
This sounds a lot like the question you asked in your other thread http://forums.mikeholt.com/showthread.php?t=190734

What is it that you are trying to understand about 250.122?
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Trying to understand both 250.122 (b) and 250.122 (f). I increase size of phase conductors to 2 sets of 500 kcmil due to voltage drop but the increased size is also parallel i.e. 2 sets 500 kcmil. I get 1/0 gnd from 250.122 (b) but 250.122 (f) says full size. Full size of what phase conductors which gives 500kcmil gnd or circuit braker ratimg which is 400 amps giving #3 gnd? Which 250.122 (b) size gnd or 250.122 (f) size would apply?

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I don't see the word "full size" in 250.122((F)
(F) simply tells you how to size conductors when you install parallel phase conductors in the same raceway (a) or multiple raceways (b).
If you increase the you still need to follow (B).
 
In this context the wording "full size" means that each raceway needs to have a "full size" EGC based on 250.122. The EGC is sized according to the OCPD ahead of the circuit. So if your OCPD requires a #1/0 when you use one raceway it would require a 10-#1/0's if you used 10 raceways.
 
DrSparks said:
Yes. You must increase the size of the EGC proportional to the increase in size of the ungrounded conductors, but the EGC never needs to be larger than any phase or grounded conductor.

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250.122 says that the EGC never has to be larger that the "circuit conductors". IMO opinion, the total cross sectional area of all of the conductors connected in parallel would be the "circuit conductors", which would be 1000 kcmil in this case.
 
Doubling the feeder size seems excessive.
You didn't state all of the circuit parameters...
If 480V-3P, 320A PF-0.85 load, 1-set 500kCMIL, 465' = 2.7%VD
Going to 2-sets of 250kCMIL will give you 2%VD.
 
MyCleveland said:
Doubling the feeder size seems excessive.
You didn't state all of the circuit parameters...
If 480V-3P, 320A PF-0.85 load, 1-set 500kCMIL, 465' = 2.7%VD
Going to 2-sets of 250kCMIL will give you 2%VD.
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Question is not regarding %vd. I know 2 sets 500 kcmil gives approriate %vd.

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codequestion said:
... Which 250.122 (b) size gnd or 250.122 (f) size would apply?
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Both rules apply. You have to up-size the EGC because you up-sized the ungrounded conductors. The up-sized equipment grounding conductor is the the EGC for the application of 250.122(F).
 
codequestion said:
Increase to what ground size in circular mills?

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The code section says increased proportionally. You doubled the the circular mill area of the ungrounded conductors so you have to double the circular mill area of the EGC. Look up the circular mill area of the equipment grounding conductor that is required for your 400 amp OCPD and double that area. Round up to the next standard conductor size. Table 250.122 requires a 3AWG copper EGC for a 400 amp OCPD. Chapter 9, Table 8 tells you that the circular mill area of 3 AWG is 52620. Doubling that is 105,240. The smallest standard conductor with a circular mill area that exceeds 105,240 is 1/0 at 105,600. You need a 1/0 in each of your parallel raceways.
 
I can't put my finger on the exact wording that states the fact but since it calls for a full size EGC when running parallel raceways, I would say you need a 1/0 in each.
If you had elected to run the 2-500s in one raceway then, as you calculated, you need a 1/0 EGC due to your increasing for voltage drop. Multiple raceway rules say all conduits take "full size" EGC which to me means a 1/0.
 
don_resqcapt19 said:
The code section says increased proportionally. You doubled the the circular mill area of the ungrounded conductors so you have to double the circular mill area of the EGC. Look up the circular mill area of the equipment grounding conductor that is required for your 400 amp OCPD and double that area. Round up to the next standard conductor size. Table 250.122 requires a 3AWG copper EGC for a 400 amp OCPD. Chapter 9, Table 8 tells you that the circular mill area of 3 AWG is 52620. Doubling that is 105,240. The smallest standard conductor with a circular mill area that exceeds 105,240 is 1/0 at 105,600. You need a 1/0 in each of your parallel raceways.
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He already answered his own question correctly in the OP. :)
 
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