Panelboard in detached garage

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Old 02-19-20, 08:58 AM
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Panelboard in detached garage

Is it permissible to install a 60 amp panelboard (actual 100 amp rating since they don't make 60 amp panelboards anymore) in a detached garage and have it being feed from the 100 amp main service panel in my home? The garage would have a 60 amp breaker as the main shutoff which would then feed the circuits in the garage. 100 amp main panel in home would have 60 amp breaker feeding the garage.

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02-21-20, 12:07 PM
Zorfdt
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No issue with using a higher-amperage breaker in the subpanel. It's just there as a disconnect.
The important over-current protection device is the 60A breaker in your main panel that's sized to protect the 6ga wire.

No issue with using a 100A (or even 200A) panel in your garage.
 
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Old 02-19-20, 10:20 AM
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No problem at all. I'd suggest you install a 100 amp main breaker panel in the detached garage and not worry about having a 60 amp main breaker. The 100 amp breaker will simply be a panel disconnect and the protection of the feeder and subpanel will be the 60 amp subfeed breaker in your main panel. You will need to install a separately purchased ground bar in the subpanel and DO NOT bond the neutral bus to the panel box. You will need to install a 4-wire feeder to the garage; 2 hots, 1 neutral and 1 equipment grounding conductor. You will also need to install at least one ground rod at the garage connected to the ground bar you field install with #6 copper, I prefer #6 bare stranded ground wire. The local AHJ can advise you on whether you need one or two ground rods. If two rods are required, they must be at least 6 feet apart. For the feeder I would use 3 - #6 THWN-2 and 1 - #10 Green THWN-2 all in 1" PVC conduit.
 
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Old 02-19-20, 10:39 AM
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Thank you, CasualJoe, for your reply. I asked this question because I did not think there would be an issue doing this type of installation, but I had a local electrical outfit tell me that it was not allowable by NEC standards. Something about the 60 amp garage panel, when combined with the 100 amp-rating of my main service panel combining to create a possible situation where the load request was greater than the house's main breaker. I thought it odd, but did not want to argue with the guy, as he was the expert. I think I am going to contact our city's electrical inspector and see what he has to say.

Again, CasualJoe, thank you for your reply to my question.
 
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Old 02-19-20, 10:51 AM
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I had a local electrical outfit tell me that it was not allowable by NEC standards. Something about the 60 amp garage panel, when combined with the 100 amp-rating of my main service panel combining to create a possible situation where the load request was greater than the house's main breaker.
That's total nonsense, I'd stay away from that contractor in the future. That guys comment is like saying that you wouldn't be allowed to add up all the circuit breakers in a panel and have them exceed the rating of the main breaker. It's almost a crime that licenses are sometimes issued to companies that have no idea what is in the NEC and have never attended a code class.

Think of it like this. Suppose you have a 100 amp service and in that main 100 amp panel you have a 50 amp range circuit, a 30 amp electric dryer circuit, a 20 amp washer circuit and a 20 amp dishwasher circuit. Under that guys reasoning your service would be full and at 100% and you could have no more circuits, no lights and no receptacle outlets.
 
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Old 02-19-20, 10:59 AM
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Hello CasualJoe. Thank you for sharing your knowledge, I really appreciate it.
 
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Old 02-19-20, 11:27 AM
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Technically you are supposed to do a load calculation before adding on to what you have. Most of the time it is not an issue. Are you going to have an EV car charger? Worst case scenario would be with a garage that has 14KW electric heat. That would be 60 amp continuous load that would likely mean your main 100 amp service would need upgraded.
 
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Old 02-21-20, 07:07 AM
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Hello Astuff,

Thank you for you comment. No, will not have an EV car charger, nor any high KW electric heating device/system. House has gas stove/oven and gas clothes dryer, so there are really no high-amperage devices used in home.

I spoke with city electrical inspector and he said there would be no problem, absent the possible issue you raised (which is not a concern in this situation).

With respect to CasualJoe's comment about just going with the 100 amp main breaker (used as a disconnecting device) being fed by the 60 amp breaker in my home's service panel, do you concur that this setup would not be in violation of any NEC code? My concern would be that doing so could give the false impression that the panel is feed with 100 amps. This would not be of concern to me, but I don't know if AHJ would have an issue with it.

Thank you.
 
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Old 02-21-20, 12:07 PM
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No issue with using a higher-amperage breaker in the subpanel. It's just there as a disconnect.
The important over-current protection device is the 60A breaker in your main panel that's sized to protect the 6ga wire.

No issue with using a 100A (or even 200A) panel in your garage.
 
Astuff, CasualJoe voted this post useful.
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Old 02-22-20, 08:31 AM
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Thank you, Zorfdt, for your reply. I appreciate you taking the time to share your expertise.

 
 

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