Service Entrance Equipment

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blues

Member
Location
Nevada
I have 2500kva xfmr. at 12.47-480v with a secondary OCPD of 3000a/3p with 1#4/0 gounding electrode conductor connectec to "xo" and 8 sets of 4#500kcmil copper conductors & 1#4/0 gnd., each in 4" conduit feeding 3000amp service entrance equiptment.
My question is are not the 8 sets of 4#500 papallel feeders ground condutors feeding 3000amp SWBD. at that point sized based on the rating or setting of the OCPD thus requiring 400kcmil conductors in each conduit.

Thank you
Dan Craven
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
If it is truly a service (as opposed to a SDS), 250.24(C)(2) allows the grounded conductor to be sized in accordance with the phase conductors in each pipe assuming it meets the requirements of 220.61 and is not smaller than 1/0).
In your case it appears a 1/0 would have been o.k. as long as it met the load.

If it happens to be an SDS, it appears the same statistics would apply but under 250.102(C)
 
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bob

Senior Member
Location
Alabama
Augie
I would never question your vast superior excellent knowledge of the code. However, I believe there is a misunderstanding of the question. Blues is installing
8 runs of 4 500 kcm to a 3000 amp breaker. He has a 500 kcm neutral in each conduit. He is also installing a 4/0 grounding conductor in the same conduit.
His question was regarding the size of the 4/0 based on table 250.122. My question to blues is why are you installing the 4/0 conductor? I assume it was on the plans.
When connected, the 4/0 will be in parallel with the 500 kcm neutral. I don't think the code requires you to do this. As augie pointed out the neutral(grounded conductor)
is sized based on the tables he listed. Table 250.122 gives you the minimum equipment grounding conductor.
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
Bob, always question me for, as you can see, reading (correctly) is not my forte' :D

back to the drawing board
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
O.K., now that I actually read the question
:D
I think (not doing that well today) that we are back to the "service" vs SDS story. If this is a service, then I am in agreement with Jumper in that the grounded conductor would normally suffice and there is no need for the grounding electrode conductor to accompany the other wires and if it were installed and connected to the same location on both ends it would be a violation as Bob indicates.

If this is an SDS installation, then 250.30(A)(2) would require an "equipmemnt bonding jumper" to be run with the power conductors to the 1st disconnect means (unless you met Exception 2 of 250.30(A)(1)--which you probably do). If that jumper is needed, it again could be sized per 250.102(C) and a 1/0 would be allowed.

(Check me , Bob, not a good "brain" day)
 
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