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Old 10-10-2012, 02:55 PM   #1
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Two 20amp curcuits running from House panel to detached garage


Hello Everyone..
I have a few questions that I have not seen a specific answer to on this forum. First off I have a 200amp service in my house and have a detached Garage which is about 25ft away. The service panel for my house is located on the side wall that faces the garage. A few years back a friend who does electrical work, helped me run 2 20amp 12/2 with ground from the service panel out the side of my house and through conduit buried at least 2 feet and entering into my garage. At this point 2 20amp GFI's were installed and then one circuit was used to run 5 receptacle outlets on the one circuit. The other was used 2 sets of outdoor lighting and lighting for inside the garage. Note that No ground rod was used and circuits rely on the ground from the service breaker panel.
My questions came about after reading this forum which made me wonder if there was a problem with this configuration. The GFI's were installed to disconnect the power to the garage in the event it was needed. Should there be a grounding rod outside the garage? and if so how would you go about making the connections.
If any other info is needed please ask. Thanks for any help you can give me.

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Old 10-10-2012, 03:09 PM   #2
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Two 20amp curcuits running from House panel to detached garage


You can't have 2 separate circuits feeding the structure. NEC 225.30. You could have run it as an MWBC and been OK.

225.30 Number of Supplies. Where more than one building or other structure is on the same property and under single management, each additional building or other structure that is served by a branch circuit or feeder on the load side of the service disconnecting means shall be supplied by only one feeder or branch circuit unless permitted in 225.30(A) through (E). For the purpose of this section, a multiwire branch circuit shall be considered a single circuit.

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Last edited by AandPDan; 10-10-2012 at 04:58 PM. Reason: typo
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Old 10-10-2012, 04:47 PM   #3
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Two 20amp curcuits running from House panel to detached garage


Thanks so much for your reply since after reading posts on here made me wonder if the connection I was using was safe. At the risk of sounding dumb, can you tell me what WMBC means? Also what suggestion do you have that will remedy this without ex stream cost. Some detailed instruction or a place to find it would be very helpful.
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Old 10-10-2012, 04:57 PM   #4
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Two 20amp curcuits running from House panel to detached garage


It was typo, I meant MWBC - multi wire branch circuit. Sorry about that. That's where you have two hots on opposite legs and they share a neutral.

It doesn't mean your installation isn't safe. It just means that you don't meet Code.
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Old 10-10-2012, 05:08 PM   #5
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Two 20amp curcuits running from House panel to detached garage


If you make it a MWBC you still have the same capacity if the current is balanced between the two hots.

It is not too costly for materials to install a sub panel, but there is not that much point to it since it won't give you any more power than a MWBC.

With a MWBC, you are going to have to reconfigure your GFIs.
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Old 10-10-2012, 05:27 PM   #6
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Two 20amp curcuits running from House panel to detached garage


If I were to make the changes would I use a single 12/3 with ground and remove the old 2 12/2 with ground Then use a double 20amp breaker instead of the 2 single breakers? As for as sub panel, what would be best to use? and if doing that would I then need to drive a ground rod outside my garage?
Sorry and hope I asked the questions proper. It won't be long and winter will be here so if I have to make the changes I need to do so quickly or wait until spring. I have had no issues what so ever with the setup as it is now, and the GFI breakers work well when wanting to disconnect the power to the garage.
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Old 10-10-2012, 05:36 PM   #7
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Two 20amp curcuits running from House panel to detached garage


If you have the multiwire branch circuit from the house to the garage, you can still put ground fault interrupter receptacles in the garage. The restriction is, if you wish to use one GFCI receptacle to protect other equipment and receptacles, you must run 2 conductor cable from that GFCI (its load terminals) to the additional locations that don't have their own GFCIs.

The MWBC can continue to locations with additional GFCI receptacles.

If you used a GFCI breaker back at the main panel then you don't need GFCI receptacles.

The ground rod (you need two, six feet apart) is not required unless you have a subpanel. You will need a subpanel if you plan on using more than 20 amps at 240 volts. You may choose to put in heavier wires back to the house now for more amperes in the future.
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Old 10-10-2012, 05:39 PM   #8
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Two 20amp curcuits running from House panel to detached garage


You don't need a subpanel but you do need a disconnect.

I'd run the 12-3 into a junction box with a double pole 20 amp switch, from there, connect to your existing wiring.
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Old 10-10-2012, 05:53 PM   #9
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Two 20amp curcuits running from House panel to detached garage


I am one that does not normally ignore code BUT:

Given what you have, the only change I would make is install a 2 pole 20 amp breaker in the house panel and connect the 2 circuits to it.
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Old 10-10-2012, 06:34 PM   #10
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Two 20amp curcuits running from House panel to detached garage


Out of curiosity, what color was the outer sheathing on those two runs of 12/2 ?
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Old 10-10-2012, 06:54 PM   #11
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Two 20amp curcuits running from House panel to detached garage


I just check the entry to the service and they are both Gray

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