UPS feeder size

[mstrlucky74]

No info except that it's 120/208 3P 4W panel and not sure what size for the ground and if it needs a neutral. I'm thinking 4#3's(only 20' feet away from panel). What size ground? Based on 250.122 I'm thinking #8.Thanks.

 

[infinity]

#3 THHN and #8 EGC. You could use #4's if the calculated load is 85 amps or less.

 

[mstrlucky74]

#3 THHN and #8 EGC. You could use #4's if the calculated load is 85 amps or less.

Thanks.

 

[ron]

I would suggest to bring 4W + ground to the UPS. Some smaller UPSs are not "online" type, and essentially pass power through until a power quality issue is detected. If 120V is available on the output, it is likely that you need a neutral on the input.

Granted some better UPS's do have some isolation from input to output and might not need a neutral on the input, but better to wire nut it off if you don't need it, than not have it.

Did they tell you the 90A CB? If you sized it be sure you are giving capacity headroom for full load plus losses and battery recharge.

 

[steve66]

Most UPS's installation manuals will have a table that lists input and output wire sizes. They normally seem to oversize the wiring for some reason or another. Might be worth an RFP to get an answer in writing before you start installing.