Running Outdoor Conduit

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Old 04-30-08, 09:58 AM
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Running Outdoor Conduit

I am going to run a power line underground from my house to a driveway gate. The power requirements at the gate will be less than 100 watts. The run is 70 feet. I will run the power cable through pvc (or whatever you recommend) 18" underground.
1)I was told elsewhere to use 10 gauge thhn for the 70-foot run. On this website, thwn was recommended. Do I need 10 gauge, and do I need thwn?
2) I want to tap into a box on a 15-amp circuit that has almost no other power loads. That ok?
Thanks for any advice!
 
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Old 04-30-08, 10:10 AM
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Originally Posted by mike s. View Post
I am going to run a power line underground from my house to a driveway gate. The power requirements at the gate will be less than 100 watts.
Are you only hooking up the gate, or will you have a general purpose receptacle for yard tools, christmas lights, etc?

I will run the power cable through pvc (or whatever you recommend) 18" underground.
1/2" PVC conduit is just fine.

I was told elsewhere to use 10 gauge thhn for the 70-foot run.
#10 is an overkill for 100W at 70 ft. If you're only hooking up the 100W gate, #14 wire is sufficient. If you're also putting in a general purpose receptacle, I would recommend #12 wire.

On this website, thwn was recommended. Do I need 10 gauge, and do I need thwn?
THWN is required -- it is the waterproof version of THHN. If you look closely at the printing on the wire virtually all THHN is also THWN.

I want to tap into a box on a 15-amp circuit that has almost no other power loads. That ok?
What does that circuit power?
 
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Old 04-30-08, 10:22 AM
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Now that you mention it, I probably should put in a receptacle at the gate for power tools/christmas lights.
I can do #12 thwn...would that be single-wire w/ a separate ground wire, or is 12/2 thwn (assuming they make it) ok?
The 15-amp box I'd be tapping runs receptacles in the garage (the occasional power tool).
If necessary, I can run a new circuit from the power box; it's just a much bigger pain. If I do, should that be 15, 20, 30 amp? (I'm guessing 15)..
Thanks for your quick & knowledgeable reply!
 
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Old 04-30-08, 10:33 AM
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Originally Posted by mike s. View Post
I can do #12 thwn...would that be single-wire w/ a separate ground wire, or is 12/2 thwn (assuming they make it) ok?
You buy it in individual conductors -- get black, white and green.

The 15-amp box I'd be tapping runs receptacles in the garage (the occasional power tool).
It would be okay to extend this circuit if you wanted to.

I can run a new circuit from the power box; it's just a much bigger pain. If I do, should that be 15, 20, 30 amp? (I'm guessing 15)..
With #14 wire, it's 15A; with #12 wire, it's 20A.
 
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Old 04-30-08, 10:37 AM
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Perfect, thank you!
 
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Old 04-30-08, 12:20 PM
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Put in 12-3 so you can switch the lights back at the origin. Or to provide an extra circuit if needed in the future for your guardhouse.

Also, as long as you are trenching, put some ENT or burial-rated communication wire in for future use in case you want to have an intercom, camera, etc. This wiring cannot go in the same conduit with 120 VAC, as you probably know.
 
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Old 05-01-08, 09:31 AM
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12/3 to put in a switch at the house sounds smart. But I was under the impression that thwn was single wire.
What is ENT? Maybe I could put in two conduits....
Is "burial rated comm wire" supposed to be in conduit, or can it be just in the ground? What kind of wire is comm wire?
good ideas, thx. "Guardhouse"?? Ha Ha, no, this is not for a mansion or a castle...
 
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Old 05-01-08, 10:16 AM
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Originally Posted by mike s. View Post
12/3 to put in a switch at the house sounds smart. But I was under the impression that thwn was single wire.
It is single. You could pull in a red or blue wire (in addition to the black-white-green) to be the switched leg for a light at the gate.

What is ENT? Maybe I could put in two conduits....
Is "burial rated comm wire" supposed to be in conduit, or can it be just in the ground?
ENT (electrical non-metallic tubing) is a flexible plastic conduit, but that doesn't really matter because it can't be used underground.

You could install a second PVC conduit in the trench if you ever intend to put in communications wire like CCTV, security system, intercom, etc.
 
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Old 05-01-08, 02:09 PM
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Unless you had a need for a switched light (or saw the near-future need for one), instead of running an extra wire, I'd run a pull string along with it. Down the road it would be pretty easy to pull another wire or two through if you needed it.

Then again, pulling all the wires at first is always easiest... so depends on how near-term your need is.
 
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Old 05-01-08, 02:17 PM
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If you run this from the load side of a GFCI, you don't even need the conduit (except where above ground and down to the bottom of the trench). You can then bury UF-B cable as little as 12 inches down (in most situations).

Rather than put a receptacle out at the gate, it's a lot easier to simply use an outdoor extension cord when needed from a reeptacle on the house. This would mean that you could use 14/2 UF-B to the gate.
 
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Old 05-01-08, 02:39 PM
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Originally Posted by ibpooks View Post



ENT (electrical non-metallic tubing) is a flexible plastic conduit, but that doesn't really matter because it can't be used underground.
Good point. I mention ENT because in some applications the NEC will not be enforced with low-voltage. In other words, some jurisdictions do not require a permit for low-voltage work.

ENT is NOT approved for burial under the NEC, but for the DIYer it is sometimes a scavenger hunt to find continuous duct that is rated for burial. Riser-Gard or Carflex are better choices. I use 1-1/4" utility innerduct. As long as it's warm, it is a lot easier to install and pull than gray PVC.

Here's a FAQ from
http://www.carlon.com/Flexible%20Rac...s_ENTFAQs.html

Do you sell an ENT product, such as your Blue Flex-Plus that is listed for direct burial?
Article 331 of the 1999 NEC or Article 362 of the 2002 NEC, Uses, not permitted, prohibits ENT from being direct buried. We sell a telecommunications/data inner duct called Riser-Gard, which can be direct buried, but it is not for electrical applications. We also sell a product called P&C Flex, which is not UL listed, but is used by utility companies for direct burial. Carflex liquid tight flexible nonmetallic conduit can be direct buried up to and including 1" sizes.
 
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Old 05-01-08, 03:14 PM
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I agree it's a technicality to not use ENT underground; I don't understand why the code forbids it. ENT is okay to use in poured concrete, under concrete slab floors, around corrosive chemicals, and various other wet locations. It doesn't make sense that buried under topsoil is somehow substantially different than the approved locations.

Mike- certainly consider John Nelson's suggestion as well. He offers a plan for the least expensive installation that will meet your present need.
 
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Old 05-04-08, 07:41 PM
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Thanks for all the suggestions. I don't have a problem using PVC conduit, and will use at least 1" and add comm wires (what are the specs for "comm wire"?) and maybe strings.
 
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Old 05-05-08, 09:53 AM
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Just in case this was your plan, please understand that you CANNOT run the communications cable through the same conduit as class one power circuits.
 
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Old 05-06-08, 09:35 AM
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Still not sure what comm cable is. Do you mean like coaxial or RCA?
Did not know that I can't run in same conduit with the #12 wires. Why not? This now means I have to lay two pvc conduits.
 
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Old 05-06-08, 09:54 AM
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Originally Posted by mike s. View Post
Still not sure what comm cable is. Do you mean like coaxial or RCA?
I believe he just meant communications cable which could be phone wire, coaxial, computer CAT5, intercom various other low voltage cables; whatever you wanted for a video camera or security system of some sort.

Did not know that I can't run in same conduit with the #12 wires. Why not?
The safety issue is that you wouldn't want a cable failure to energize your phone or TV set with line voltage. The practical issue is that the power lines will cause interference and humming in the phone or TV signal.

This now means I have to lay two pvc conduits.
Yes that's true if you want communication capability in addition to power. Usually what I recommend is to bury the power conduit at the bottom of the trench, backfill the trench halfway, lay the communications conduit, then backfill to grade.
 
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