What Will a Amp Breaker Feeding Detached Garage Handle

• #1

I have to supply power to a one car detached garage. There will be 2 outlets, two lights & a garage door opener. I would like to feed it with a 3 wire #12 wthe ground. Can I use a double pole 20 amp switch as the disconnect in the garage?

• #5

Re: Detached Garage

Don,

I'm not sure I agree with you on that.

210.4(A) A multiwire branch circuit shall be permitted to be considered as multiple circuits.

While this does not require it to be considered as multiple circuits I would guess that in the case of a separate building most inspectors would consider it multiple circuits.

• #6

Re: Detached Garage

For this purpose, the multiwire branch circuit is considered a single branch circuit, see 210.4 (A). The disconnect can be a snap switch see 225.26 exception and Fig 225-16 in mike holts understanding the NEC. Ground rods are not required at separate building or structure that has only one branch circuit 250.32 (A) exception, see fig 250-86 in mike holts understanding the NEC.

• #7

Re: Detached Garage

Tom,

Your 210.4(A) must read different than what's in my book since I don't see anywhere that it says that a multiwire circuit is always single circuit.

210.4(A) Branch circuits recognized by this article shall be permitted a multiwire branch circuits. A multiwire branch circuit shall be permitted to be considered as multiple circuits. All conductors shall originate from the same panelboard.

The second sentence says that they shall be permitted to be considered as multiple circuits and I think many inspectors would do so in the case of a separate structure. I don't think the intent of the coded was to only require a grounding electrode system if you have multiple grounded conductors run to the building. I think the excepting was for structures that have very limited loads and only require a single 15 or 20 amp two wire circuit.

I do agree that a switch is an acceptable means of disconnect.

• #13

Re: Detached Garage

George

Yes you may. In your application you must install a ground rod since the breaker is in the detached building.

If you install the breaker only in the house you do not need a ground rod. In this application you would run the circuit to a junction box then split this single circuit in half.

Thanxs Don. I would not have allowed this before your explaination.

Mike P.

• #14

Re: Detached Garage

Curt, In Washington State our electrical inspection agency allows a multiwire branch circuit to be run as a single branch circuit to a seperate building or sturcture. Thats the way Mike Holt explains it as well.

• #15

Re: Detached Garage

Curt, In Washington State our electrical inspection agency allows a multiwire branch circuit to be run as a single branch circuit to a seperate building or sturcture. Thats the way Mike Holt explains it as well.

• #16

Re: Detached Garage

Tom & Don,

I understand your opinion on this but I could still see it ending up in a stand off with many inspectors especially with 2 single pole breakers. I will try to remember to ask this question to a few electrical inspectors to see what they say. It still doesn't make sense to me that if you run two 2-wire circuits you need to install a grounding electrode system but if you install one 3-wire circuit a grounding electrode system is not necessary.

Wayne,

The grounding electrode conductor for the separate building is only required to be connected to the equipment ground at the disconnect for the separate building. I don't see where its required to increase the size of the equipment ground conductor between the 2 buildings to the same size as the grounding electrode conductor.

• #17

Re: Detached Garage

Tom & Don

I just had another thought. Lets say we feed a garage with a 3-wire multiwire circuit and use a 2-pole switch as the disconnect. Now from the switch we run two 2-wire cables (one for each circuit) to feed the various loads. Do you still consider the two 2-wire cables one circuit?

• #19

Re: Detached Garage

Don,

I haven't looked at 250.32 when making any of my posts but should have before making my last post. I was think that it was the number of circuits in the building but its the number of circuits that supply the building so if the so if the multiwire circuit before the switch is accepted one circuit the two 2-wire cables after the disconnect switch would be acceptable.

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Source: https://forums.mikeholt.com/threads/detached-garage.16020/