Service Capacity

[Fitzdrew516]

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

 

[Smart $]

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]

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]

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 $]

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

 

[jumper]

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

Could be. Never did an isophase so I do not think of it.

If isophase, is the grounded isolated also? If yes, a bit oversized I imagine.

 

[Smart $]

...If isophase, is the grounded isolated also? If yes, a bit oversized I imagine.

With 4 conduits, grounded also isolated... and likely oversized. Doubt they have 5400A of line to neutral loads.

 

[Fitzdrew516]

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

Got it! :thumbsup: Thanks.

 

[Strathead]

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]

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]

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 $]

...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.



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