Need help choosing correct size main breaker for existing subpanel

[bartleyhs]

DIY homeowner here. I need advice, but will hire a pro if major rewiring needs to be done.
I purchased a home with a 200amp service. There is a detached garage about 15’ from the house. I dont think the subpanel in the garage was wired correctly.
There are currently three 4awg aluminum branch feeders (direct burried) to the subpanel in the garage with no ground conductor. Also the main panel and subpanel were not grounded to earth. I already added a bare copper wire going to a rod (earth) on both the main and subpanel.
Currently there is a 40amp breaker in the main panel that feeds the garage. There is no main shutoff in the garage.

I have 3 questions.
1: I think I am supposed have a main shut off at the garage since it is a detached building and the panel has 12 slots (24 circuit) Is that correct?
2: I think a 40amp breaker is too small for 4 awg aluminum wire. What is the correct breaker size?
3: Should there be a ground conductor between the two panels?
Thanks for the help.

 

[Megawatt]

DIY homeowner here. I need advice, but will hire a pro if major rewiring needs to be done.
I purchased a home with a 200amp service. There is a detached garage about 15’ from the house. I dont think the subpanel in the garage was wired correctly.
There are currently three 4awg aluminum branch feeders (direct burried) to the subpanel in the garage with no ground conductor. Also the main panel and subpanel were not grounded to earth. I already added a bare copper wire going to a rod (earth) on both the main and subpanel.
Currently there is a 40amp breaker in the main panel that feeds the garage. There is no main shutoff in the garage.

I have 3 questions.
1: I think I am supposed have a main shut off at the garage since it is a detached building and the panel has 12 slots (24 circuit) Is that correct?
2: I think a 40amp breaker is too small for 4 awg aluminum wire. What is the correct breaker size?
3: Should there be a ground conductor between the two panels?
Thanks for the help.

bart if you have a subfed panel in your garage it’s supposed to have an equipment ground. The 40 amp breaker is the right size for # 4 aluminum depending on the insulation which can go from 40-55 amps. It’s not unusual to not have a main breaker since your protection is in your main panel and you need to remove the ground rod. The 12 space 24 circuit panel is correct if you use slim line breakers

 

[bartleyhs]

bart if you have a subfed panel in your garage it’s supposed to have an equipment ground. The 40 amp breaker is the right size for # 4 aluminum depending on the insulation which can go from 40-55 amps. It’s not unusual to not have a main breaker since your protection is in your main panel and you need to remove the ground rod. The 12 space 24 circuit panel is correct if you use slim line breakers

Thank you for the reply. If I understand you correctly,
1. I need to remove the grounding rod from the subpanel, but not the main panel.
2. The equipment ground = a 4th wire connecting the sub panel to the main panel’s ground?
3. No shut off is required at the detached garage.
4. Everything else is correct.

One more question.
If I wanted to increase the subpanel to 60 or 70 amp what size wire would I need to run for that?

Thanks again

 

[Megawatt]

Thank you for the reply. If I understand you correctly,
1. I need to remove the grounding rod from the subpanel, but not the main panel.
2. The equipment ground = a 4th wire connecting the sub panel to the main panel’s ground?
3. No shut off is required at the detached garage.
4. Everything else is correct.

One more question.
If I wanted to increase the subpanel to 60 or 70 amp what size wire would I need to run for that?

Thanks again

You are correct on all questions. Google Article 310 (15 ) B of the NEC and it will show you a table of all size wires and the amperage of copper and aluminum left side of the table is copper and right side is aluminum and sorry about the delay in answering your questions. Good luck my friend and by the way I’m licensed in NC and Florida

 

[bartleyhs]

You are correct on all questions. Google Article 310 (15 ) B of the NEC and it will show you a table of all size wires and the amperage of copper and aluminum left side of the table is copper and right side is aluminum and sorry about the delay in answering your questions. Good luck my friend and by the way I’m licensed in NC and Florida

The charts are what confuse me. Everything makes sense until it gets to the amperage of the breaker.
I looked more closely at the direct burial wires running from house to garage. It is aluminum AWG 4 type RHH. According to this chart it is rated at 90 degrees, but I understand I need to use the 75 degree column because the breaker is rated 75 degrees, Right? So it says in that column 65, which I thought meant a 60 or 70 amp breaker. That was why I questioned the 40 amp breaker in my original post. But you said 40 is correct, so that is where I am left scratching my head. I am obviously missing something, but cant figure out what.
Also, for the ground conductor I need to run between the two panels, does it need to also be AWG 4 or can it be a smaller size, and should it be copper or does it also need to be aluminum to match the others?
Thank you so much for your help.

 

[Megawatt]

The charts are what confuse me. Everything makes sense until it gets to the amperage of the breaker.
I looked more closely at the direct burial wires running from house to garage. It is aluminum AWG 4 type RHH. According to this chart it is rated at 90 degrees, but I understand I need to use the 75 degree column because the breaker is rated 75 degrees, Right? So it says in that column 65, which I thought meant a 60 or 70 amp breaker. That was why I questioned the 40 amp breaker in my original post. But you said 40 is correct, so that is where I am left scratching my head. I am obviously missing something, but cant figure out what.
Thank you so much for your help.

View attachment 57303

Yes that is correct always go by the 75 degree C scale. I said that what ever type insulation dictates the amperage
[automerge]1586738578[/automerge]

Yes that is correct always go by the 75 degree C scale. I said that what ever type insulation dictates the amperage

Type RHH insulation is good for 75 amps so you could up your breaker size
[automerge]1586738812[/automerge]

Yes that is correct always go by the 75 degree C scale. I said that what ever type insulation dictates the amperage
[automerge]1586738578[/automerge]

Type RHH insulation is good for 75 amps so you could up your breaker size

If I was you and you want a bigger breaker I would probably install a 60 amp

 

[bartleyhs]

Yes that is correct always go by the 75 degree C scale. I said that what ever type insulation dictates the amperage
[automerge]1586738578[/automerge]

Type RHH insulation is good for 75 amps so you could up your breaker size

AHA, I see now that the type of wire insulation was the thing I was missing in the equation. I originally thought it was all about the size of the wire, now I’ve got it.

One more question since you know Florida and then I will leave you alone.
While I was purchasing the house my inspector said the panel in the garage was the wrong box, so the owner had an electrician come out and replace it. The old box was left here and I am seeing that the old box has an inspection sticker from 1980, but the new box does not have an inspection sticker, which I understand can be an insurance issue. Is it possible to get an inspection from the city done for work that was completed before I bought the house?

 

[Megawatt]

AHA, I see now that the type of wire insulation was the thing I was missing in the equation. I originally thought it was all about the size of the wire, now I’ve got it.

One more question since you know Florida and then I will leave you alone.
While I was purchasing the house my inspector said the panel in the garage was the wrong box, so the owner had an electrician come out and replace it. The old box was left here and I am seeing that the old box has an inspection sticker from 1980, but the new box does not have an inspection sticker, which I understand can be an insurance issue. Is it possible to get an inspection from the city done for work that was completed before I bought the house?

You can go to your local code enforcement office and ask for permits that has been drawn on your address. If you want to pay them they will do a safety check for you. I bet they changed that panel and didn’t draw a permit or it would have a sticker

 

[bartleyhs]

Than

You can go to your local code enforcement office and ask for permits that has been drawn on your address. If you want to pay them they will do a safety check for you. I bet they changed that panel and didn’t draw a permit or it would have a sticker

I think you’re right. Thanks for all your time in answering my questions.

 

[Megawatt]

Than

I think you’re right. Thanks for all your time in answering my questions.

You are quite welcome my friend and good luck