12/3 wire (2, 20amp circuits) to garage?

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Old 01-20-07, 01:44 PM
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12/3 wire (2, 20amp circuits) to garage?

I have a detached garage that has no electricity about 50 ft from the house. In the house I have a 12/3 wire coming from 2, 20 amp circuits that go nowhere. I would like to get them out to the garage through plastic conduit (24" deep) and was wondering if that could be done through the conduit with a box in the garage where one hot would go to 2 receptacles (light power tool use) and the other would go to a light fixture? Would both receptacles need to be GFI or just the first one? If I need a grounding rod or subpanel out at the garage, could I work the 12/3 wire into that confirguration or would I have to get into the main house panel (I am not interested in getting in the main house panel).
 
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Old 01-20-07, 02:25 PM
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You are suggesting a multiwire circuit to the garage. This is legal and provides twice as much power as a single circuit. Yes, you can do this.

There are rules about conduit depth, etc. I suggest 24 inches deep for the conduit, and then I suggest individual wires in the conduit, rather than using cable. However, you could use UF cable in the conduit. The conduit must be run and assembled before the cable is installed.

You then need a disconnect inside the garage. I suggest that you run the conduit into a large box inside the garage. There you can install two switches. At this box split the circuit into two separate circuits. Control each circuit with a switch.

Only the receptacles in the garage need to be GFCI protected.

Make certain that either a 240 volt circuit breaker protects this in the house panel, or that the two 120 volt breakers are on separate legs of the incoming 240 volts.

One other note. I would use 10 gage wire from the main panel to the garage. This will help limit voltage drop.
 
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Old 01-20-07, 04:19 PM
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thanks

Would both receptacles in the garage need to be gfi receptacles or just the first one? If I have a bunch of 12/3, could that be something I just use for the wiring after I split the circuit (i.e. do they frown on using 12/3 and capping the empty wire off as opposed to just using 12/2?)
 
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Old 01-20-07, 05:02 PM
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Recommend putting a GFCI receptacle at the beginning run of each circuit.


>>> GFCI >>>>>Recept>>>>Recept>>> etc.
 
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Old 01-20-07, 07:01 PM
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The receptacles in the garage need to be GFCI protected. This can be done in one of several ways.

You can use a GFCI breaker. In your case it wold have to a 240 volt GFCI breaker. I don't recommend this, as any trip would trip the lights as well as as the receptacles.

You can use a GFCI receptacle at each receptacle This gets expensive.

You can use a GFCI receptacle as the first receptacle and have it protect all the others.

Yes, you can use 12-3 instead of 12-2, but I do not recommend it. 12-3 is harder to work with, and you may want it for something else in the future.
 
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Old 01-21-07, 07:27 PM
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Question GFCI on Multi-Wire Circuit

I thought there were issues with using a single GFCI receptacle at the beginning of a series of receptacles in the case of a multi-wire circuit. I was under the impression that a GFCI receptacle could be used at each receptacle on a multi-wire circuit, but not to protect a series of receptacles due to potential current imbalance in a multi-wire circuit.

I don't know, maybe I am off in the weeds.
 
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Old 01-21-07, 08:49 PM
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Also keep in mind that if the receptacle is serving something which by it's nature makes said receptacle un-usable in normal circumstances (such as behid a refrigerator or above head for a garage door opener), the receptacle does not need to be GFCI protected.

this might be another reason to go with local GFCI protection, rather than the breaker. You don't want a nuisance trip to take out the refrigerator power...especially when you are not at home.
 
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Old 01-21-07, 09:34 PM
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As I stated i my earlier post, split the circuit at the entrance to the garage. Once you split the multi-wire circuit, there are no issues with GFCI receptacles related to the multi-wire circuit, since at that point you don't have one.

The concern about a refrigerator being GFCI protected is a good one, but only if you have a refrigerator (or freezer) in the garage. If you do, then I suggest you wire differently, so that you can still use a single GFCI for protection of the circuit.
 
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Old 01-23-07, 07:55 AM
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disconnect

Racraft, you mentioned just using a large box with two switches as the disconnect. Is there anything in particular I would need in this regard (special box, special switches, special wiring), or is it that easy (bringing the two hots of the 12/3 to two switches inside a box then running them in different directions off the switches)?

Thanks,
 
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Old 01-23-07, 08:58 AM
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A normal double gang switch box with two normal two way switches. Connect the hot wires from the 12-3 feed one to each switch. Connect the hot wire from each 12-2 that you will run in the shed, one to each switch. Connect all neutrals together. Connect all ground wires and pigtail to the switches and to the box if the box is metal.
 
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Old 01-24-07, 09:54 AM
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Cool Sub-Panel

---OR---

You could just go ahead with a sub-panel where service would enter the Garage. Home Depot, Lowe's and Menard's all have panels of all sizes by Square-D, Siemens, GE, Cutler-Hammer, to name a few.

A simple 6-circuit panel would suffice. You could put half the outlets on one 20A breaker on one 120V leg, and the other half on a 20A breaker feeding from the other 120V leg. Lights on a third, and you still have three empty slots, allowing future upgrades, if your plans change.

The box and three circuit breakers should total about $25-$30, depending on location, brand, and size.

I did a subpanel for my garage last year and it was neither expensive nor complicated, and it gives me all the flexibility I need. Panel was a Square-D Homeline 6-circuit, 100A panel ($15), and two 20A and two 15A breakers ($15) for a total of just over $30. Since all the wiring and outlets were already in place, the box & breakers were my only material expense. Just a little time to re-configure things at the new panel.

If you send me an e-mail, I can send pics.


Steve
 
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Old 01-24-07, 07:27 PM
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A sub panel would require a ground rod, etc. I certainly would not put in a sub panel for a 20 amp feed.
 
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Old 01-25-07, 09:12 AM
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If the double-pole switch is functioning as a safety-disconnect, then a subpanel is a must, because this kind of switch is not suited for this function. Yes, It will work, but it would be soooo againse Code. If a 6-ckt is too much, then a 4-circuit or even a 2-circuit panel (even cheaper) would suffice.
 
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