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Really Long Panel Feeder - How to Connect to Panel and Feeder Breaker?
I'm working a project involving great distances from a main switchboard or power panel to some 250A 480/3 panels.
By Vinny Galbo on 20 May, 2018 - 8:08 pm

I'm working a project involving great distances from a main switchboard or power panel to some 250A 480/3 panels. The champion is an 850-foot run. In order to keep voltage drop to less than 3 percent, I calculated the need for 4 sets of 350 MCM per phase at an 80 percent load on the panel (200A) for this longest run.

My question is, I haven't found a 250A panel that can accept 4 x 350 MCM per phase at the main lugs, nor a switchboard breaker that can do so either. Do we need to spot a wiring box at each end to reduce the feeder size to "normal" (1 x 250 MCM) at each end?

Sorry for the elementary question - I've just never run into these distances before. I've always been able to space my mains as needed to reduce feeder distances, but not in this cavernous building.

Thanks for your help!

By Vinny Galbo on 23 May, 2018 - 12:30 pm

This is the direction that we are currently heading. We plan to group each set of four conductors onto a pair of commercially-available stud terminals with a link bar across them, and take something more manageable out to the load and source. We are looking at Weidmuller's WFF series. https://www.clrwtr.com/UserFiles/CT/Documents/Weidmuller/Weidmuller-Screw-Connection-Stud-Terminals.pdf

If someone has a better solution, please share it.

How did you arrive at needing 4 x 350 MCM per phase? Maybe recheck your calcs. I'm thinking one 500 MCM per phase would result in about .075 V drop per ampere at 850 ft.

By Bob Peterson on 25 May, 2018 - 12:24 am

There's no reason you can't splice smaller wires on to the feeder at each end. Polaris connectors work pretty good for this kind of thing. With that much wire you might want to give serious consideration to using aluminum it will save you a lot of money.