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# What size wire to use for a 100A garage sub panel, with a run of 120 feet?

#1
07-22-18, 07:14 PM
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Join Date: Jul 2018
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What size wire to use for a 100A garage sub panel, with a run of 120 feet?

I am Wiring in a 100A subpanel for a new garage off of our 200 amp main panel. The run is about 120 feet, part of it inside across the basement and the rest will be ran underground. Found a wire size calculator, and it says to use 2/0 aluminum or #1 copper, is this overkill? Wondering what size cable to use.

#2
07-22-18, 07:33 PM
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Welcome to the forums.

The wire size is correct. How do you plan on wiring the job ?
Cable in the basement to junction box then convert to conduit underground ?

#3
07-23-18, 11:05 AM
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I was planning on running 2/0-2/0-2/0-1 SER cable across basement and then through the wall to outside where it would then be ecased in conduit underground to the garage, all in one continuous length of wire. Would it be a better idea to use a junction block?

#4
07-23-18, 11:12 AM
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We had an electrician do something similar a while back. He used aluminium as it was an outside run and alu cheaper than copper.

#5
07-23-18, 06:31 PM
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Originally Posted by szman23
I was planning on running 2/0-2/0-2/0-1 SER cable across basement and then through the wall to outside where it would then be ecased in conduit underground to the garage, all in one continuous length of wire. Would it be a better idea to use a junction block?
SER cannot be placed underground, even in conduit. You need to switch to wire that is allowed underground such as THWN,XHHW, or MHF(USE/RHH/RHW)

#6
07-24-18, 06:42 AM
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I am Wiring in a 100A subpanel for a new garage off of our 200 amp main panel.

100 amps is a lot of power, do you really need a full 100 amps? You can still use a 100 amp main breaker panel with a smaller feeder such as 6-3 UF-B cable which can be run the entire distance, both above and underground, and fed with a 2 pole 60 amp breaker.