Tap conductor parallel

[hhsting]

Ok so I have 4000A service disconnect which feeds to 400A fused disconnect with 3 phase 2 sets of (4#3/0 AWG + 1 #3G) 10 feet or less from service disco.

These are feeder taps conductors so I asked to provide 250.122(G) equipment grounding conductor size. I am surprised at the response I got they provided 2 sets(4#3/0 + 350kcmilG). They say it comply per NEC 2014 section 250.122(G) equipment grounding conductor is not required to be larger than phase conductor. According to them 3/0=168 kcmil and 2x3/0 = 336 kcmil so it is not larger than phase. Yes they are providing 350kcmil each conduit.

Ok please correct me if I am wrong but should this not be 2 sets(4#3/0 + 3/0G)? Is feeder taps equipment grounding conductor size 3/0G or 350 kcmil?

 

[hillbilly1]

Being an equipment ground, which goes by ocp size, not conductor size, I would think the #3 would be sufficient. If they were paralleling 3/0's for 4000 amp, then I could see the 350's

 

[hhsting]

Being an equipment ground, which goes by ocp size, not conductor size, I would think the #3 would be sufficient. If they were paralleling 3/0's for 4000 amp, then I could see the 350's

How so these are feeder taps? Ok let me state post #1 in different way but same question:


Please see attach sketch. 4000A breaker load side has 400A feeder size of 2 sets of 4#3/0 to 400A fused disconnect.

What size equipment grounding conductor should be provided?

 

[augie47]

350! A faultl would be fed by both 3/o feeders.

 

[infinity]

Ok so I have 4000A service disconnect which feeds to 400A fused disconnect with 3 phase 2 sets of (4#3/0 AWG + 1 #3G) 10 feet or less from service disco.

These are feeder taps conductors so I asked to provide 250.122(G) equipment grounding conductor size. I am surprised at the response I got they provided 2 sets(4#3/0 + 350kcmilG). They say it comply per NEC 2014 section 250.122(G) equipment grounding conductor is not required to be larger than phase conductor. According to them 3/0=168 kcmil and 2x3/0 = 336 kcmil so it is not larger than phase. Yes they are providing 350kcmil each conduit.

Ok please correct me if I am wrong but should this not be 2 sets(4#3/0 + 3/0G)? Is feeder taps equipment grounding conductor size 3/0G or 350 kcmil?

I agree that 350 kcmil is the correct size for the 4000 amp OCPD. You cannot parallel two smaller EGC's to make a larger one.

 

[augie47]

(hillbilly1: please see mail)

 

[hhsting]

I agree that 350 kcmil is the correct size for the 4000 amp OCPD. You cannot parallel two smaller EGC's to make a larger one.

My tapped conductors are 2 sets of 3/0. 250.122(G) says size equipment grounding conductor based on 4000A OCPD but shall not be required to be larger than the tap conductor. So how can equipment grounding conductor be larger than 2 sets of 3/0 AWG?

 

[augie47]

You answered your own question in the original post. The 2 3/0s combined are 336 and a 350 is the closest size without going under that.

 

[hhsting]

You answered your own question in the original post. The 2 3/0s combined are 336 and a 350 is the closest size without going under that.

Alright I am still getting confused. I am sorry. Your saying it should be 4#3/0 + 1#350 kcmil gnd each in 2 conduits. So if I have 2 sets it would be 700 kcmil equipment grounding conductor total which is way larger than tapped conductors 336 kcmil? Equipment grounding conductor size is not required to be larger than tapped conductors NEC 2014 section 250.122(G).

As oppose to if I have 4#3/0 + 1#3/0 gnd each in 2 conduits then I have total equipment grounding conductor size of 336 kcmil which is not larger than tapped conductors?

 

[augie47]

Based on 250.122 the EGC for a 4000 amp breaker would be a 500, but the parallel rule says no larger than the tap consductors. If you are uisng 3/0s to feed a tap to a 400 amp OCP device they would have to be in separate conduits to have adequate ampacity so you would need an EGC in each conduit and,as noted, since a fault could feed both ways you would need a 350 in each.
Trust whomever gave you the respaonse,

 

[hhsting]

Based on 250.122 the EGC for a 4000 amp breaker would be a 500, but the parallel rule says no larger than the tap consductors. If you are uisng 3/0s to feed a tap to a 400 amp OCP device they would have to be in separate conduits to have adequate ampacity so you would need an EGC in each conduit and,as noted, since a fault could feed both ways you would need a 350 in each.
Trust whomever gave you the respaonse,

Ok but 250.122(G) says “..shall not required to be larger than the tapped conductor. ” (singular) ?

 

[augie47]

but you don't have a singular tap conductor, you have 2 tap conductors.. one LAST time.. if you had a short, power would flow thru BOTH your tap condcutors and you have two conduits and the Code requires a full size in each conduit.

 

[hhsting]

but you don't have a singular tap conductor, you have 2 tap conductors.. one LAST time.. if you had a short, power would flow thru BOTH your tap condcutors and you have two conduits and the Code requires a full size in each conduit.

Thank you augie47 and all others for your inputs. I really appreciate.