Newbie question on installing subpanel in attached garage

[pinkchry]

In Norcal. Have some experience with doing electrical stuff in the house but this is the first time I'm installing a sub panel. Being purposefully dumb to make sure that I don't miss anything.

I have a 50amp EV outlet run from my main panel using 8awg (previously installed by a licensed electrician). I now have a 125amp subpanel that I'd like to install in place of the outlet and run a few outlets in the garage using that.

Pictures of the EV outlet run and the subpanel are at https://imgur.com/a/5Pl9mP6

It looks. to be a simple matter of connecting the two hots and the neutral to the lugs and the ground to the ground bus bar on the left. Anything obvious I'm missing?


Thanks!

 

[Jkcolo22]

I believe that 8awg will be way too small for a 125amp panel. Wire size calculator says that 125amp panel will require 2 gauge. The 8 gauge is actually questionable for a 50amp ev outlet. My understanding is that those really pull close to the full 50 amps.


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[Jkcolo22]

It actually says right there on your panel that 2/0 is required on your main lugs.

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[pinkchry]

Hmmm. So I can't use this panel with a lower awg for what will effectively be a 50amp subpanel?

 

[mike93lx]

Oh God, that is completely wrong.
A larger panel is fine. You could put in a 200a panel for the sub...doesn't matter. You will continue to protect it with a smaller breaker at the main panel.

Your panel requires at least 4 gauge on the main lugs, but you may be able to feed it via a breaker on the buss as well. Hopefully one of the real electricians here can help.

 

[mm08822]

It actually says right there on your panel that 2/0 is required on your main lugs.

No, it clearly provides a conductor range for the lug.

Smallest size = #4
Largest size = 2/0

As Mike stated, Op will need to backfeed a cb to feed the panel b/c of the existing #8's. A cb holddown listed for that panel will be required in that case.

OP, make sure neutral bar is not bonded to grd. (I can't get your pic to load anymore).

Main panel should have a 50a cb in it.

You could put any size cb in panel to supply power. 100a works.

OP, Pull every cb out of that panel and clean it up. Dust it off, blow it out, etc. (Use no fluids)

 

[mm08822]

I believe that 8awg will be way too small for a 125amp panel. Wire size calculator says that 125amp panel will require 2 gauge. The 8 gauge is actually questionable for a 50amp ev outlet. My understanding is that those really pull close to the full 50 amps.


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#8 THHN is good for 50a.

 

[pinkchry]

Main panel should have a 50a cb in it.

You could put any size cb in panel to supply power. 100a works.

I'm confused by this. Why would it make sense to have a 100a cb even if the wire feeding it is 8awg? I was thinking of going with a 50amp cb (similar to that feeding this subpanel to avoid confusion).


Thanks

 

[Innovate1]

I'm confused by this. Why would it make sense to have a 100a cb even if the wire feeding it is 8awg? I was thinking of going with a 50amp cb (similar to that feeding this subpanel to avoid confusion).

Thanks

The 50A breaker in the main panel provides the over current protection. The breaker in the subpanel being used back fed is really just used as a switch. You can use anything there - smaller or larger than 50A although using something smaller doesn't make sense as it limits the current to the panel to lower than needed for the wire size. But you are right that using a 50A might reduce confusion. If you already have something bigger you can just use it.

 

[pinkchry]

Also to make it absolutely clear to me - I should buy a double pole qo breaker and connect the red/black to the breaker and the neutral to the neutral bar and the ground to the egc on the left - connect the breaker and attach it using the cb holddown?

Thanks!

 

[MattT]

I'm confused by this. Why would it make sense to have a 100a cb even if the wire feeding it is 8awg? I was thinking of going with a 50amp cb (similar to that feeding this subpanel to avoid confusion).

It doesn't make any sense to use an expensive 100A breaker when you only need 50A. Personally I'd use a 60A which is the largest cheap breaker.

 

[MattT]

Also to make it absolutely clear to me - I should buy a double pole qo breaker and connect the red/black to the breaker and the neutral to the neutral bar and the ground to the egc on the left - connect the breaker and attach it using the cb holddown?

Correct. Just make sure the neutral bar isn't bonded to the ground before you connect the neutral & ground.

 

[mm08822]

I'm confused by this. Why would it make sense to have a 100a cb even if the wire feeding it is 8awg? I was thinking of going with a 50amp cb (similar to that feeding this subpanel to avoid confusion).

Also to make it absolutely clear to me - I should buy a double pole qo breaker and connect the red/black to the breaker and the neutral to the neutral bar - connect the breaker and attach it using the cb holddown?

Thanks

It's as Innovate stated.
In your case, the cb being added is to just get around the fact that the main lugs can't accommodate wire smaller than #4.

You ask for a specific part # - You could purchase a QO250CP. This is a 2 pole 50 amp circuit breaker.

Connect:
red/black to the breaker,
neutral to the neutral bar and
green to ground bar.

Get the Hold downkit # from your panel label's accessory list

 

[mike93lx]

Edit: whoops, my answer is right in the subject.

 

[alfredeneuman]

If it's in the structure it still must have a 4 wire feed

 

[mm08822]

Is this in the same structure as the main panel or separate?

If separate, it must be a 4 wire feed and you need to ground rods

Lol! Read title. See pic! . Stuff happens.........

 

[pinkchry]

Thanks all. I'll get the required parts connect them and post a picture for further critique. Appreciate the help!

 

[wyliesdiesels]

Is this in the same structure as the main panel or separate?

If separate, it must be a 4 wire feed and you need to ground rods

Every panel after the first means of disconnect is required to be 4-wire no matter where its located

 

[mike93lx]

Every panel after the first means of disconnect is required to be 4-wire no matter where its located

Already noted here and I deleted my post....