Service Capacity

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Fitzdrew516

Senior Member
Location
Cincinnati, OH
Please see attached clip of an existing one line drawing.

I am trying to figure out the service capacity of the existing service to this building. It has a 2500A switchboard, but no main (6 disconnect set up). It looks like I need to derate per the more than 3 CCC rule, but I am not quite sure bc I'm not sure if I'm reading this correctly. Can anyone help me out with this?

Thanks,
- Drew
 

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Smart $

Esteemed Member
Location
Ohio
From what I gather, your lateral has eight (8) 500kcmil ungrounded conductors per phase, two per conduit, and four (4) 500kcmil grounded conductors, one per conduit. Derating for 6 ccc's per conduit applies.

8 × 380A × .8 = 2432A
 

Fitzdrew516

Senior Member
Location
Cincinnati, OH
From what I gather, your lateral has eight (8) 500kcmil ungrounded conductors per phase, two per conduit, and four (4) 500kcmil grounded conductors, one per conduit. Derating for 6 ccc's per conduit applies.

8 × 380A × .8 = 2432A

Now I'm more confused, haha. I see that there are (4) conduits with (7) #500's in each conduit which means (28) total 500's. I'm not seeing how your numbers are adding up to that. Could you break it down a little more for me?
 

jumper

Senior Member
From what I gather, your lateral has eight (8) 500kcmil ungrounded conductors per phase, two per conduit, and four (4) 500kcmil grounded conductors, one per conduit. Derating for 6 ccc's per conduit applies.

8 × 380A × .8 = 2432A

Now I'm more confused, haha. I see that there are (4) conduits with (7) #500's in each conduit which means (28) total 500's. I'm not seeing how your numbers are adding up to that. Could you break it down a little more for me?

8 #500 per phase x 3 phase = 24 #500 + 4 #500 (grounded) = 28 #500 total.
 

Smart $

Esteemed Member
Location
Ohio
8 #500 per phase x 3 phase = 24 #500 + 4 #500 (grounded) = 28 #500 total.
Hmmm.... just dawned on me this could be isophase also. Outright 7 conductors per phase/neutral in one conduit each.

If that be the case... 7 × 380A × .7 = 1862A
 

Strathead

Senior Member
Location
Ocala, Florida, USA
Occupation
Electrician/Estimator/Project Manager/Superintendent
8 #500 per phase x 3 phase = 24 #500 + 4 #500 (grounded) = 28 #500 total.

But they are also service laterals so they are only required to be able to carry the load. In Florida, the secondaries I have done have all been sized to the NEC. In California, however, I saw three parallel 750 aluminum supplied and installed by PG&E feeding a 2,000 amp service more than once. And the NEC calculated load was 1,100 or 1,200 amps. Their rules are different.
 

jumper

Senior Member
But they are also service laterals so they are only required to be able to carry the load. In Florida, the secondaries I have done have all been sized to the NEC. In California, however, I saw three parallel 750 aluminum supplied and installed by PG&E feeding a 2,000 amp service more than once. And the NEC calculated load was 1,100 or 1,200 amps. Their rules are different.

Yes. I am not sure why you quoted me though, I was merely clarifying Smart's post for the OP on the number of conductors.
 

Strathead

Senior Member
Location
Ocala, Florida, USA
Occupation
Electrician/Estimator/Project Manager/Superintendent
Yes. I am not sure why you quoted me though, I was merely clarifying Smart's post for the OP on the number of conductors.

Yeah, my mistake, I actually intended to quote the one that showed the ampacity, which was smart's and obviously got lazy. Sorry to both of you.:slaphead::slaphead::slaphead:
 

Smart $

Esteemed Member
Location
Ohio
...I actually intended to quote... smart's ...
But they are also service laterals so they are only required to be able to carry the load....
As opposed to what? Service entrance must be sized to load factored 125% of continuous portion. That requirement does not apply to laterals or drops, which are flat out minimum sized at 100% load.

And on the POCO side of the service point, not even sized per NEC. :D



No matter what in the OP's case, service rating is limited to 2500A, according to the one-line.
 
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