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Old 05-21-2010, 09:57 AM   #1
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Underground Wiring From House to Garage


My father-in-law says I need to get the garage wired to install an electric garage door opener, several outlets, lights inside and security lights outside. I don't think this is all necessary but he's paying for it so I'm going along with his master plan. I have a few questions and concerns:

1. Do I need a permit?

2. How far underground does the wiring need to be?

I've dug a 18 inch deep trench 20 feet from the house to the garage but encountered drainage pipes. The trench goes through an area where there is gravel and Tyvek for drainage, some sort of pipe that I dug through and another pipe that is 1 foot underground that I decided to leave alone.

3. Is it okay to run the underground wire through this?

4. Do I have to continue digging under the third pipe to get to an 18 inch depth?

Thanks!
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Old 05-21-2010, 10:03 AM   #2
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Underground Wiring From House to Garage


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Originally Posted by Virginhomeowner View Post
My father-in-law says I need to get the garage wired to install an electric garage door opener, several outlets, lights inside and security lights outside. I don't think this is all necessary but he's paying for it so I'm going along with his master plan. I have a few questions and concerns:

1. Do I need a permit?

2. How far underground does the wiring need to be?

I've dug a 18 inch deep trench 20 feet from the house to the garage but encountered drainage pipes. The trench goes through an area where there is gravel and Tyvek for drainage, some sort of pipe that I dug through and another pipe that is 1 foot underground that I decided to leave alone.

3. Is it okay to run the underground wire through this?

4. Do I have to continue digging under the third pipe to get to an 18 inch depth?

Thanks!
If you run your wire in PVC conduit, which is probably the best way to go, you need 18" of cover. Which means probably about a 20" deep trench. Any given point along the entire conduit must have 18" of ground cover over it.

Oh, and ALWAYS call to have underground utilities marked before you do any digging. Not only because digging into a buried electric/gas line will kill you dead, but also because if you don't call, and you damage some utility pipes or wire, it could cost you hundreds of thousands of dollars. Not sure about where you are, but here in MN it's free to have them come out and mark all the utilities buried on your property.

Last edited by McSteve; 05-21-2010 at 10:06 AM.
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Old 05-21-2010, 10:19 AM   #3
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Underground Wiring From House to Garage


Most places Yes you need a permit & inspections
They will usually look at the trench once its dug down to depth

Are you running just one circuit ? MWBC ? Small sub-panel ?

You do need 18" depth to the top of the pipe
*edit* depth depends upon conduit used, if it goes under a road/driveway, if you want to put concerete above pipe you can go shallower

Last edited by Scuba_Dave; 05-21-2010 at 11:18 AM. Reason: more info
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Old 05-21-2010, 11:03 AM   #4
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Underground Wiring From House to Garage


Search "sub panels" "garage panel" above in the search box. Once you open that, you can read all about your project and all the details until you can read no more. Trust me. Every single question you have will be answered using this method.
Of course should you require any verification or just plain help. "Holler at Us" As they say here in SC.
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Old 05-21-2010, 11:11 AM   #5
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Underground Wiring From House to Garage


Virgin

Here's a couple drawings to base your project on and any further questions you may have.

First is using conduit and a sub-panel in the garage and the second is a simple multiwire branch circuit that you could run using a direct bury method not using conduit. Your depth of trench would then need to be 24".

If father in-law is footing the bill I would use conduit in either case. If you use pvc conduit install individual wires like THWN/THHN which are common at the big box store. Then at the disconnect (switch or subpanel) you may switch to another wiring method like nm-b (romex).

There are some differences in what is required between the two installations.

I'm short on time at the moment but be sure to ask about how to configure the multi-wire single branch circuit to the garage. Several people here can help you with installing a multiwire and the differences for grounding etc.....

You can also just run one 12/2 g to the garage and use a single pole switch as the disconnect. This will give you one 20 amp circuit versus two 20 amp circuits using a multiwire supply and 12/3g to the garage.
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Last edited by Stubbie; 05-21-2010 at 01:38 PM.
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Old 05-21-2010, 06:15 PM   #6
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Underground Wiring From House to Garage


the picture above is nice, but I would add bedding sand around the conduit, warning tape, and a piece of pressure treated lumber above it.
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Old 05-21-2010, 09:34 PM   #7
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Underground Wiring From House to Garage


I am considering a similar project in the near future. I am wondering if a data cable can be run through the same PVC conduit as the electrical.
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Old 05-21-2010, 10:53 PM   #8
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I am considering a similar project in the near future. I am wondering if a data cable can be run through the same PVC conduit as the electrical.
Negative, unless you can find CAT-5 with a 600V insulation. NEC says all wiring in the same raceway must have the same insulation voltage rating. Also, I think there are restrictions on having unrelated wiring in the same raceway.
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