Detached Garage

johnmstrks

Member
Location
Mh11370!
Occupation
Engineer
The garage will have a subpanel with several circuits (lighting, exterior, car bay and wall outlets) all in EMT. It will be fed underground in PVC by 6/3 AWG w/ground. 230.79(D) calls for a minimum 60 amp disconnect. It seems this rules out the 50 amp circuit breaker at the main panel as a disconnect means as 6AWG is only rated for 55 amps. Where does the code require the 60 amp disconnect to be located? And, what type of disconnect means would be required? Two ground rods will be installed 6 feet apart with bare 6AWG.
Thanks again,
John
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
Will this be a service or is it fed by a feeder (you said sub-panel) originating at another building? For a feeder the code section is 225.39 for the disconnecting means size which is similar to the section you've mentioned for a service. 225.52 tells you the location of the disconnecting means.

You also said "underground in PVC by 6/3 AWG w/ground" that sounds like a cable. Will it be a cable in PVC or individual conductors?

Welcome to the Forum. :)
 

johnmstrks

Member
Location
Mh11370!
Occupation
Engineer
Good morning. Thank you for the response.
There is a main panel located at the house. A two pole 50 amp breaker at that main panel feeds two hots, a neutral, and a ground. The four are individual conductors in an underground PVC pipe. The garage will have a sub panel. It has not been determined how many circuits that sub panel will have, potentially more than six.
Thank you.
 

infinity

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Staff member
Location
New Jersey
Occupation
Journeyman Electrician
I would use a panel with a 100 amp main circuit breaker at the garage since that's the cheapest option. Because you're using #6 AWG copper conductors you can use the 75° ampacity of #6 AWG which is 65 amps.
 

Dennis Alwon

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Staff member
Location
Chapel Hill, NC
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Retired Electrical Contractor
And remember a #6 rated at 75C can be on a 60 amp overcurrent protective device if the calculated load is 55 amps or less. Section 240.6
 

drcampbell

Senior Member
Location
The Motor City, Michigan USA
Occupation
Engineer
Suggestion: Install conduit twice as large as necessary today, to future-proof against the need to supply two fast-charge EV chargers. Very little added cost today, prevents the need for trenching again tomorrow.
 

Dennis Alwon

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Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
If it is only going to be on a 50 amp breaker then #8 would work if you believe that section 225.39 really only means the physical disconnect enclosure. IMO, it should be fed with #6 and a 60 amp overcurrent protective device.

I know we can argue this all day but it makes no sense. When I wrote a proposal to clarify it their comment was simple with no help in understanding it. No, what is written is what they mean-- or something like that.

I know this is a bit off but, in that case, we could run #10 with a 30 amp breaker at the builder and install a 60 amp disconnect with a 60 amp breaker and we would be compliant. That is ridiculous, IMO-- maybe Don knows more about this reason for this section.
 
An electrical panel located in a detached garage would not fall under the requirements of a "service" that you referenced in the original post (230.79(D)). It is only a subpanel, connected to the main service in the house, and therefore, does not need to meet the 60A minimum requirement. You should be able to size the circuit out to the garage based on the connected load you will have in the garage, regardless. If you only have a connected load of 20A or 30 A, you could have a 40A overcurrent device in the main panel in the house. This will also save on the wire size routed to the garage.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
An electrical panel located in a detached garage would not fall under the requirements of a "service" that you referenced in the original post (230.79(D)). It is only a subpanel, connected to the main service in the house, and therefore, does not need to meet the 60A minimum requirement. You should be able to size the circuit out to the garage based on the connected load you will have in the garage, regardless. If you only have a connected load of 20A or 30 A, you could have a 40A overcurrent device in the main panel in the house. This will also save on the wire size routed to the garage.
You are correct this is not a service but 225.39 does have disconnect requirements that are similar to the minimum sizes for service disconnects. And as you've stated the feeder does not need to be 60 amps.
 

mikeames

Senior Member
Location
Germantown MD
Occupation
Teacher - Master Electrician - 2017 NEC
I know this is a bit off but, in that case, we could run #10 with a 30 amp breaker at the builder and install a 60 amp disconnect with a 60 amp breaker and we would be compliant. That is ridiculous, IMO-- maybe Don knows more about this reason for this section.
I see no issue with it. I look at the garage side as simply a disconnect like a switch. I don't do it this way but I support it being an option.
 
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