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What size PVC Conduit for 10/2 underground wiring

Posted by wilboud (My Page) on
Wed, Feb 9, 11 at 17:13

I have a lighting project. Using 10/2, I plan to run 165 feet of wire underground to a pole for lighting. The wire will be totally enclosed within conduit.

On the pole I also want a waterproof receptacle box. I plan on running wire through each pipe length as we go along (no string).

1) What minimum size conduit will allow 10/2 to run freely without too much issue?

2) What size breaker should I use for a receptacle and 100 watt (Dusk to Dawn Lighting)light at the end of 165 feet of 10/2?

3) What kind of wire should I use, buried in conduit?

4) Is 10/2 over-board, should I be using 12/2?

Thanks

Boudreaux
from Cajun Country


Follow-Up Postings:

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RE: What size PVC Conduit for 10/2 underground wiring

You shouldn't probably be using 10-2 for anything in conduit. What sort of 10-2 cable where you considering.
You must use wet rated conductors underground, even in conduit. NM cable is not going to cut it.

I would suggest either using individual THWN conductors or forgoing the conduit and using UF.

If you're only envisioning 15A on the circuit, you could get by with #12 wiring.

The breaker should be no larger than 20A and 15A would also be OK. You'll need GFCI protection as well.

1/2" would be fine for up to 4 #10 THWN conductors (you'll need 3). I might size up a bit just to make the pulling easier. You need to be down 18" if you're using sched 80 (which is advisable).


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RE: What size PVC Conduit for 10/2 underground wiring

"On the pole I also want a waterproof receptacle box. I plan on running wire through each pipe length as we go along (no string)."

Ya mind if I answer in reverse order?

4) Is 10/2 over-board, should I be using 12/2?

It depends on what you want to be able to use at the receptacle. 165' is long enough that voltage drop becomes an issue, so if you plan on plugging in, say, a compressor or heavy duty power tool, you'd probably want a 20-amp receptacle. Assuming an 80% load (16 amps), #10 wire is just about right. Anything less will cause an unacceptable voltage drop at that amperage. But if the receptacle won't be used for anything more than something like a small electric weed whacker or a few christmas lights, then #12 should be OK.

3) What kind of wire should I use, buried in conduit?

THWN individual conductors (not a "10/2" cable). You'll need three: hot (black), neutral (white) and a bare or green-insulated ground.

2) What size breaker should I use for a receptacle and 100 watt (Dusk to Dawn Lighting)light at the end of 165 feet of 10/2?

It depends on your requirements (see above). But let's go with a 20 amp, whether you use #10 or #12.

1) What minimum size conduit will allow 10/2 to run freely without too much issue?

You say you're planning to pull the conductors each time you add a 10' joint, right? That's not the way I'd do it, if only because PVC cement and wire insulation don't get along very well -- wet cement can eat through the insulation. That's one good reason why it's better to assemble the conduit run and then pull the conductors.

But if you do it your way, 3/4" PVC conduit oughta work. (Even 1/2" is possible.) If you assemble the run first and then pull the conductors, I probably choose1". Keep in mind that PVC conduit is quite cheap.

***

Adding: Your trench should be at least 18" deep -- more if the run will be subjected to alligator damage. :-)


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RE: What size PVC Conduit for 10/2 underground wiring

Now I've never done a pull as long as yours, but the slickest trick I've seen used on a run of approx. 110' was the sparky tied his pull string to a common plastic grocery bag, then sucked it through to the far end with a SHOP VAC! SLICK!

will-b, FORGET that pulling each segment along the way as you weld the PVC--as noted by terr-tom, it's not just tedious, it's a recipe for disaster. If anything, do a strong PULL STRING that way, with a "leader" of old fish tape or 6-10ga. bare solid wire that's a bit longer than your conduit segments. Then pull all 3 wires with one string. If there's only 2 large radius sweeps, I'd lube only the string-to-wire "knot" (after streamlining it in electrical tape), and just have someone on the feed end, making sure all 3 reels are spinning freely on "axles", and the pricey THWN is running kink-free.

Believe me, once you get going with the PVC weld cement, you're NOT going to want to stop/pull/fidget/check/restart/etc.

I also second going 3/4" minimum on the PVC, and even 1" cause it's so "roomy" and still fairly cheap. After all, everyone always wants to add MORE circuits to any given yard/house/garage/outbuilding, never LESS. Larger diameter = easier pulls.

Oh, and FOR SURE get the conduit with the MOLDED-IN coupler on the end... half the joints and 1/4th the time and hassle, fewer total fittings to buy. One-man assembly-line time! Mind the direction of flare vs. direction of pull.


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RE: What size PVC Conduit for 10/2 underground wiring

With a pull of this length you definitely want to oversize the conduit. It will make an easier pull. Also, suck in string with a shopvac as posted above, then use this string to pull in some thin rope. Use the rope to pull in the wire. This is really a two man job. One to pull and one to feed the wire to keep it from tangling, put on lube etc. Make sure you can communicate with each other so that the wire doesn't get damaged, and no one loses a finger from over zealous pulling;)


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If you have some Obama stimulus money, you can hire...

Make sure you can communicate with each other so that the wire doesn't get damaged, and no one loses a finger from over zealous pulling;)

Nyuk, nyuk, nyuk... wise words, touche'! Much cursing and family strife can be avoided w/ today's Bluetooth headsets and a few minutes airtime... or hire bikini girls w/ semaphore flags--TWINS are best, but pricey--LOL!

Seriously, you'll be MUCH happier just doing one complete stage at a time: TRENCH the whole run at one time, lay in and weld the PVC in one session, BURY the conduit in one job, THEN commence the pulling ops... you can put the boxes on the ends last, for easier clear-path pulling.

Oh, and then check back in with tales of woe and triumph! It's how we all learn... every job's unique... sort of... ;')


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RE: What size PVC Conduit for 10/2 underground wiring

Or just use an actual fish tape.

It is more than stiff enough to be pushed through.

Technically you are not allowed to pull wires as you go in conduit systems.
The entire system should be assembled before the first pull.


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RE: What size PVC Conduit for 10/2 underground wiring

Well, I have reviewed all the information above, and I'm very please. Thank you all......!!!

I feel that I'll go with 1" conduit (conduit is cheap ...right???) from the electrical supply through already welded conduit, through the 2nd 90 (facing up), and then 3/4" conduit up the pole, four feet to the receptacle box, then 10 feet up to the DTD light. GFCI will be a must ...right???

I have decided to use 12awg wire (single conductors) with a 15amp breaker.

Now, since I posted here, I have discovered that UF-B is allowed in conduit, but I have a feeling THWN (single conductor) would probably be cheaper.

I know UF-B is a buryable cable if I choose to use it. My reasoning behind conduit is safety in years to come, in case someone decides to stick a shovel in the ground. And to keep the alligators from chewing the wire....LOL...!!!

Thanks again for the info.

Wilson Boudreaux
from Cajun Country


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RE: What size PVC Conduit for 10/2 underground wiring

Yup, GFCI is a must.

Good luck!


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RE: What size PVC Conduit for 10/2 underground wiring

You'll have to bury UF-B at least 12" (if you use the exception for a single GFCI-protected small circuit) or 24" otherwise which (or you could put concrete over it). Even SCHED-80 PVC (that's what you were going to use, right?) needs to be down at 18"

Yes, you definitely need a GFCI on the receptacle, though it would behoove you to use a GFCI breaker in the panel to cover everything.

Aligators we don't have to deal with up here in the Virginia and North Carolina.


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