Subpanel installation in detached garage

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  #1  
Old 02-07-15, 05:07 PM
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Subpanel installation in detached garage

Hello, I am installing a subpanel in a detached garage. I plan on installing a 60 Amp Breaker in the main panel. Then run a 4 wire (Gauge to be determined) Line to the detached garage and into the subpanel. Should the Subpanel have a 60 Amp “Main” Breaker and 4- 20 Amp single breakers or should it be no “Main” Breaker and only have the 4- 20 Amp Breakers (in the Subpanel)? I also plan on installing a ground rod at the detached garage. Also, what gauge wire should the main line be between the Main Panel & the Subpanel? The run is approximately 100 feet.

I also plan on installing the main line in a PVC Conduit 24 inches deep. Is that OK? I’ve read 18 inches without conduit and I tend to over do things….
 
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Old 02-07-15, 05:34 PM
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You need a local disconnect at the sub-panel. If the panel cannot accommodate any more than 6 circuits then those six circuit breakers are sufficient for the disconnect but if it will allow for more than six circuits then you need a separate disconnect. If you use a main circuit breaker panel the size of that main circuit breaker is irrelevant as it is ONLY a disconnecting means, although it must be equal to or greater rating than the supply CB in the service (main) panel. With a 60 ampere supply breaker the sub must have at least a 60 ampere CB used as the disconnect.

IF you are going to be using a full 60 amperes then you might want to have #4 conductors for the hot and neutral conductors to allow for voltage drop. You would also use a #8 for the equipment grounding conductor. If the primary loads are 240 volts you MAY be able to use a smaller neutral for the unbalanced load but that rarely occurs in a sub-panel installation. If you will rarely, or never, use the full 60 amperes then you can use #6 conductors for the hot and neutral and a #10 for the equipment ground.
 

Last edited by pcboss; 02-07-15 at 05:51 PM.
  #3  
Old 02-07-15, 06:13 PM
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So, I can use a subpanel with a "60 Amp Main Breaker" and 4-20 Amp Breakers. Is that correct? Also, I will use a "Main Line" that is #4/4 (4- 4 Gauge Wires in one insulation). Is that ok? What kind of "Main cable" should I use?
Thanks for the info Furd...
 
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Old 02-07-15, 06:39 PM
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You may use a panel rated at 60 amperes with a 60 ampere main circuit breaker and any number of branch circuit breakers of any rating less than 60 amperes.

If you run conduit you would use individual conductors with type THHN/THWN insulation. Two of the conductors would be #6 copper with an insulation color other than white, grey or green; one #6 copper conductor with white insulation and one #10 copper conductor with green insulation. Only if you are planning a continuous load approaching the 60 ampere limit would you then upsize the conductors as I previously stated.

I would use nothing less than one-inch PVC conduit (not water pipe) which would be sufficient even for the #4 conductors if you need to upsize for voltage drop.
 
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Old 02-07-15, 07:21 PM
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"60 Amp Main Breaker"
You won't find a panel with a 60 amp main breaker, but you can use a main lug only panel (MLO) and plug a 2 pole 60 amp breaker onto the bus and feed the panel through that breaker's lugs. This is called a backfed main breaker. The backfed main breaker will need a main breaker retaining kit from the panel manufacturer to be installed. OR.....you can just buy a 100 amp main breaker panel and the 100 amp breaker becomes the disconnect, like Furd said.
 
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