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Old 09-29-2011, 09:18 AM   #1
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Conduit for line to garage?


My house is from 1930 and I have to assume my garage is too.

I have 3 20 amp circuits in my garage and the way those circuits get there is through buried romex I guess it was cool to just do that back then. I mean buried as in they just dug down however far they felt and then covered the cable w/ dirt.

Anyways... my driveway widens right in front of the detached garage and continues along about 1/2 the garage. Next to the second half of the garage is grass. There is too much shade here and the grass doesn't really grow, in addition to that I'd like to be able to pull the car that goes next to the garage up further, so I'll be digging it up and doing pavers there.

I'll never have a better shot at burying a conduit from the garage to the house. I don't plan on touching the buried wires right now, but in the spring I plan on refreshing the electrical to the garage. Truth be told, I'll probably just have the electrician do it since he will be called to wire my kitchen anyways.

So ... thinking ahead I'd like to bury the conduit there so I have it there for when it's time.

Like I said I have 3 20 amp circuits there now, this seems to be plenty for me (garage door opener, 2 lamps, shopvac, miter saw, soldering iron etc)

SO .. that being said: What type / size conduit should I bury there?

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Old 09-29-2011, 09:39 AM   #2
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Conduit for line to garage?


If it's a detached garage, code does not allow you to have more than (1) circuit run to that building. You can get (2) if you run a multiwire branch circuit (double-pole breaker feeds 2 circuits, shared neutral wire).

The more sensible approach would be a 60A subpanel (and 2 ground rods to go with it). This would also give you the option of having 240v circuits in the garage down the road.

Whatever conduit you bury, put some rope/string in it so you can use it to pull your wire later.

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Old 09-29-2011, 09:42 AM   #3
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Conduit for line to garage?


I was pretty sure that my current setup is not "kosher" by today's code for MANY reasons LOL.

I'll probably go with a subpanel when I overhaul the electric there just so I could expand in the future.

Do you think 2" conduit would do the trick?

Yes - I will definitely be pulling rope through the conduit.
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Old 09-29-2011, 09:46 AM   #4
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Conduit for line to garage?


If you don't think you will ever need 240 volt service then a 20 amp MWBC is the easy way. Put a piece of 3/4" PVC Conduit 18" down.
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Old 09-29-2011, 10:21 AM   #5
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Conduit for line to garage?


2" is plenty big. You could get away with 1", but the bigger the better in my opinion.
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Old 09-29-2011, 10:33 AM   #6
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Conduit for line to garage?


MWBC just takes one run of 12/3 then I take it?

What type of wire would I run if I intended to install a 60amp subpanel?

realistically it's a 1-car garage. As much as I'd like to run crazy stuff out there I should probably just wait till I have a bigger garage...
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Old 09-29-2011, 10:42 AM   #7
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Conduit for line to garage?


Yes, the MWBC is one run of 12/3 w/ ground. It would give you two 20-amp circuits.

For a 60A sub, you need:

(3) x #6 THWN (black, red, white)
(1) x #10 THWN (green)
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Old 09-29-2011, 02:23 PM   #8
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Conduit for line to garage?


All right last question.......

Option A: I decide that 2 20amp circuits will be enough. I run 3/4" conduit for 1 run of 12/3.

Option B: I decide I want to go w/ a 60amp subpanel and will plan to run 3x #6 and 1x #10 - that would call for what size conduit?


Thank You.
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Old 09-29-2011, 02:58 PM   #9
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Conduit for line to garage?


Keep in mind that you cannot use romex (nm-b) cable in conduit underground. You should be running individual strands of THWN wire regardless of which option you use.

If you do the MWBC, run (4) x #12 THWN (red, black, white, green).

Conduit fill calculator:
http://www.electrician2.com/calculat...alculator.html

Minimum for option A: 1/2" Sch. 40 PVC
Mnimum for option B: 3/4" Sch. 40 PVC

I would definitely upsize either of those, probably 3/4" or 1" for option A, 1" or 1.5" for option B
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Old 09-30-2011, 08:37 AM   #10
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Conduit for line to garage?


Easy enough - I'll run 1.5" - the difference in room required and material cost is minimal.

Thank You.
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Old 09-30-2011, 09:08 AM   #11
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Conduit for line to garage?


Make sure the neutral and ground are NOT bonded together in your subpanel if you go that route. You can verify that with a continuity tester.

Also, if you do a subpanel in a detached structure you are required to drive 2 ground rods as well.

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