Size of circuit in subpanel in outbuilding

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Old 12-19-10, 10:14 PM
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Size of circuit in subpanel in outbuilding

I have a new outbuilding in the back yard. Half is a home office, the other half a shop for saws, power tools, etc. I have a 100 amp main in the house and want to run a 40 or 50 amp circuit to the outbuilding.

I wired the building with 7 circuits planned: 1 for lights, 2 for the shop outlets, 2 for office wall outlets, 1 for office equipment (computer stuff to always be on), and one for a standalone heater-a/c. I plan to have all circuits 20 amps (ran 8/2) which I rationalize because either the office or the shop will be in use, but not both at the same time.

So I will have a 40 or 50 amp (i prefer 50) run from the main breaker through buried conduit (6/3) to the subpanel in the outbuilding, and the subpanel will have 7 - 20 amp breakers in it...

Can I do this? Are there any code problems? If necessary, I can combine circuits to cut down on the number, but I like being able to keep things separate - and like I said, I will not be using everything at once - even in the shop, I will have a table saw on one circuit and bench outlets on another, and I can't run them at the same time.

I also understand there is more here, like grounding, etc that I haven't mentioned, and I know all of that has to be taken into account. Right now, I am mostly concerned with the amps and the planned circuits, as I am ready to insulate and get things finished, and I want to do it right.

It also bears mentioning that I have no single piece of equipment that will consume all available amperage when starting or on, so I could get by with 40 amps total... But again, I want to be able to have multiple circuits if possible. Thanks in advance
 
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Old 12-19-10, 10:26 PM
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So I will have a 40 or 50 amp (i prefer 50) run from the main breaker through buried conduit (6/3) to the subpanel in the outbuilding,
Do you mean you ran UF 6-3 instead of four #6 THWN in the conduit?
 
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Old 12-19-10, 10:38 PM
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Have not run the conduit yet, but I won't be using UF when I do. I have read about running 6/3 cable or individual 6 ga wires, and that is a decision to make as well, as far as which is the correct way to go.
 
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Old 12-19-10, 10:42 PM
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That is to say, 6/3 or 4 6 ga wires in conduit, not direct buried.
 
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Old 12-19-10, 10:49 PM
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I rather to run in conduit due you can able replace the conductor down the road if you have issue or upgrade in future.

#6 AWG will be plenty big with 50 amp breaker however how far is the outbuilding from the main breaker and I am sure you are aware you have to run full 4 conductors and you will have to sink two ground rods as well that per NEC code.

Merci.
Marc
 
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Old 12-19-10, 11:59 PM
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If you use a maximum of a 60 ampere circuit breaker to feed the building all you need for the equipment grounding conductor is #10 copper, that will save some money. Regardless, the grounding electrode conductor (from the sub-panel to the ground rods) needs to be no less than #6 and it must be copper.

You will need a sub-panel that has a single main breaker (any amperage equal to or greater than the circuit breaker in the house) OR a panel that cannot hold more than six double-pole circuit breakers. You could also use a 60 ampere pull-out switch ahead of the circuit breaker panel.

My personal preference in shop areas is to have a minimum of two lighting circuits so that if one craps out (or you hit a lamp with a long piece of material) you are not suddenly plunged into darkness.
 
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