Wiring my new detached garage

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Old 07-05-13, 11:11 AM
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Wiring my new detached garage

I'm sure that the following has been answered piece by piece on here, but I need a clear picture to get my head wrapped around.

I've got my garage built, and am ready to wire it up. I've got a 200 amp service at my house, with plenty of room in the box for my garage service. Even with the stove, dryer, a/c, etc all running at once, I feel comfortable with adding the garage.

It's 200' from the main panel to the garage. As for my garage, I'm not a woodworker or machinist. I'm a tinkerer, and as such the most I can imagine running would be a wire welder, a small 120V air compressor, and possibly an air conditioner, which due to the size of the place would probably be a 240V. Those might run all at the same time on occasion.

I need to know what size/type of wire im needing, how many individual wires, the size of the breakers on both ends, how to ground the subpanel (if necessary) etc.
 
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Old 07-05-13, 11:27 AM
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Depending on the welder and Ac a 60 amp service should be fine. For that you would use two #6* black (or one black, one red), one #6* white, and one #10 green THWN. 1" PVC conduit would be adequate but you might want to use 1" conduit to future proofing against needing to upsize the service.

Cheapest choice for a subpanel will probably be a 12 space or larger 100 amp main breaker kit. They come with the main breaker (used only as a disconnect) and an assortment of branch circuit breakers. Will almost always not include a ground bar. You will need to purchase that separately. At the house you will use a double pole 60 amp breaker.

In addition you will need one or two 8 foot ground rods.

*Note #6 is border line at 200 feet. You may want to go to #4 for the current carrying wires. Assuming an actual load of 50 amps you voltage drop would be 4.1% with #6.
 
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Old 07-05-13, 11:51 AM
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If I'm running four wires from my main panel, why am I grounding at the subpanel also with the rods?

Are the white neutral and the green ground going to hook together on the grounding bar? What's that going to look like exactly?
 
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Old 07-05-13, 12:27 PM
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If I'm running four wires from my main panel, why am I grounding at the subpanel also with the rods?
The green wire is your Equipment GroundIng Conductor (EGC). That protects you against shorts to metal cased devices and fixtures by providing a low resistance path to ground. The ground wire and ground rod are the Grounding Electrode Conductor (GEC) that protect against atmospheric charges. Both are required by code.

Are the white neutral and the green ground going to hook together on the grounding bar?
Never in a subpanel. That is why you have to add a ground bar. The ground bar is bonded to the metal housing and may only be use for ground wires. Neutrals go to the isolated(unbonded) neutral bar. Usually a panel comes with a bonding jumper or screw for the neutral bar but that is not used in a sub panel.

Tech info: The neutral and ground are bonded at the first OCPD (Over Current Protection Device) but only there. The first OCPD is usually your main panel but if there is a main breaker in a panel ahead of it they will only be bonded in the first panel and the main panel technically becomes a subpanel with isolated neutral and bonded ground. See also: http://www.doityourself.com/forum/el...-diagrams.html
 
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Old 07-05-13, 02:09 PM
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You are the man. That clears up a lot. Thanks!
 
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Old 07-05-13, 07:13 PM
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Please, go buy the book Wiring Simplified and read it cover to cover BEFORE you do any electrical work. It will be the best money you ever spent and it costs less than ten bucks.
 
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