Another sub-panel wire size question.

[cstmg8]

I've read a lot of threads on sub-panels, a lot. I'm still not fully clear on what I need. There is so much knowledge on here. I don't need suggestions, on what I should have put in, or what I'll be doing in my garage, or how I could save money with different equipment.....,etc

What I would greatly appreciate, is what size wire do I need to run through my unfinished basement ceiling, to my ATTACHED garage, to feed a 125 amp sub-panel supplied by a 125 amp breaker?? In Ohio.
Thank you in advance.

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[The Cobbler]

you need to include the total length of the run as it may or may not be a factor with voltage drop

 

[cstmg8]

Thanks, forgot that. It would be 60' max, as the wire runs.

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[wyliesdiesels]

What kind of main panel do you have?

Is a 125a breaker listed for use in it?

 

[mike93lx]

Assuming you can use a 125a breaker in your panel, and you don't want to run conduit, 2/0 AL ser.

https://www.wireandcableyourway.com/2-0-3-1-ground-ser-aluminum-building-wire.html

 

[mike93lx]

+1

Didn't read the rest of the thread, eh?

 

[cstmg8]

Thanks fellas, looks like the 2/0 Al is good for 135 at 75*. I think I finally have a solid plan worked out.

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[Terry D]

I believe you can use 1/0 aluminum SER, since 120 amps is not a common size for a breaker, you are allowed to go up to the next standard overcurrent device size of 125 amps

 

[pattenp]

I believe you can use 1/0 aluminum SER, since 120 amps is not a common size for a breaker, you are allowed to go up to the next standard overcurrent device size of 125 amps

True.

 

[theoldwizard1]

What I would greatly appreciate, is what size wire do I need to run through my unfinished basement ceiling, to my ATTACHED garage, to feed a 125 amp sub-panel supplied by a 125 amp breaker??

One thing DIY electrician never seem to understand is that THERE IS NO REASON TO MATCH THE BREAKER IN THE MAIN PANEL WITH THE BREAKER IN THE SUB PANEL !


You likely purchase the 125A sub panel because you want that many slot/circuits. But WHAT ARE YOUR LOADS ! Welding ? Compressor ? Table saw ? Dust collector ? Mini-split heat pump/AC ?

REALISTICALLY, you will likely never draw more than about 60A, so that is the size of the breaker you should have in your main panel. Seeing as that breaker protects the wire, the wire should be sized for 60A at your total intalled distance.

The breaker in the sub panel is really just a convenient building ON/OFF switch (electrician term is "disconnect) so that you can do work on the circuit inside that panel without having to walk back to the other panel.

 

[ard]

Might I point out the OP specifically knew this would come up and pointedly said 'dont go there'.

 

[mike93lx]

Yup, and he respectfully asked that. Some people just think they need to help when it isn't wanted.

 

[cstmg8]

Bought the wire today.
Correct sirs, I only asked the specific question that I needed answered because I already know the contributing factors of the rest of the situation.
I actually didn't buy the sub panel based on the number of slots/circuits.. I bought it because I decided that I wanted the ability to have 125 AMPS. (It's a main lug, not breaker)
The information that I didn't include, because it didn't pertain to my question, is that I will soon be pulling a circuit out of this panel to feed my detached pole building. My attached garage obviously has power, I just want a 220 outlet for the possibility of my welder, plasma cutter, heater, who knows what.
My house currently has 300 amp service with two 150 amp panels. I'm installing natural gas, eliminating the two hot water tanks, range, hot tub, and eventually furnace. When all of that is said and done, I'll put all remaining circuits into one panel and remove the other for use in the pole barn, replacing it with just a 125amp disconnect feeding the garage.

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[Bert_]

I'd run 1/0, your load will certainly be less than 120A. No real need to run 2/0 for the last 5 amps.

No way would I even consider moving a service panel just to replace it with a disconnect. A new panel for the barn is cheaper and easier than all that screwing around.

 

[cstmg8]

Yeah, it may come to that. I have a lot of money to spend on a pole barn before I'm worried about replacing working hot water tanks.
Though I did think about repurposing one for radiant floor heat.
I can at least use the breakers if I stick with square D qo.

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