Jim Ingram

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jimingram

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I have an apartment building I will be increasing the size of the service. There are no house loads on this service, only apartments. The existing service is 3PH, 120/208V, 1200 amps. I will be going up to 1600 amps. The existing 3 1/2" PVC conduit is big enough to install the larger wires needed to increase ampacity.

Since the conduits are PVC, I am permitted to run a single phase in each of the conduits. Eg. all phase A wires in one conduit, ditto for phases B & C. Each conduit will also have a neutral conductor, which is not a current carrying conductor.

Each phase will have 8 paralleled wires derated to 70% (Table 310.15(B)(2)(a)). Do I have to derate the non current carrying neutral in the same conduit to 70% also?

Thanks,
Jim
 
Hmmm The topic is Jim Ingram....
jimingram said:
I have an apartment building I will be increasing the size of the service. There are no house loads on this service, only apartments. The existing service is 3PH, 120/208V, 1200 amps. I will be going up to 1600 amps. The existing 3 1/2" PVC conduit is big enough to install the larger wires needed to increase ampacity.

Since the conduits are PVC, I am permitted to run a single phase in each of the conduits. Eg. all phase A wires in one conduit, ditto for phases B & C. Each conduit will also have a neutral conductor, which is not a current carrying conductor.

Each phase will have 8 paralleled wires derated to 70% (Table 310.15(B)(2)(a)). Do I have to derate the non current carrying neutral in the same conduit to 70% also?

Thanks,
Jim
Click to expand...
No lighting outside of the units? No outdoor recepts? NO HOUSE panel????? How many 3 1/2" conduits does one need for your POCO to allow 1600A? Should check... Have you looked at 250.24, or 310.4? Or 310.15(B)4c?
 
e57 said:
No lighting outside of the units? No outdoor recepts? NO HOUSE panel?????
Click to expand...


I have wired apartments that had a coachlight and recept on each front and rear poarch fed from inside each seperate unit. The parkinglot lights were fed from a panel on the community building where the managers office is. there was no need for a house panel on each apartment building.
 
jimingram said:
Since the conduits are PVC, I am permitted to run a single phase in each of the conduits. Eg. all phase A wires in one conduit, ditto for phases B & C. Each conduit will also have a neutral conductor, which is not a current carrying conductor.
Click to expand...
It may be permissible to group the conductors by phase, but it is not desireable because the impedance will be higher. It will also be more difficult to get the phase impedances, and voltage drops, identical. With a neutral grouped with each phase, you will also get current induced in each neutral, even if the overall neutral current adds to zero.

How many conduits?
 
jim ingram

jim ingram

There is no house panel in this wing. The house power for the common hallways comes from another wing.

there are three 3 1/2" PVC conduits. Each conduit will have eight 250 MCM copper for phase wires (current carrying conductors) and one additional 250 MCM copper for the neutral. There will be a total of nine 250 MCMs per conduit.
 
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