I ran 100amp to my detached garage a few years ago. #1 aluminum NM in the basement stapled to the floor joists, splice using Panduit splicers inside of a large junction box to #3 copper THHN. 2" LB's and PVC. PVC from the junction box to LB fitting, PVC underground 18" to other LB, PVC to electrical box in garage. Unbond ground and neutral in garage electrical box. Pound in 8' grounding rod, #6 copper to garage electrical box. Used a pull string and wire pulling lubricant, no problems with 2" PVC.
underground service wiring conundrum
- Thread starter RustyShackleford
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Right, or 21 cu-in if I decide to go up to 8awg. I looked at the 1-1/4 LB boxes I have and they ARE marked with their volume (as code requires if they are used for junctions) and well in excess of 21 cu-in. Plus I'm seriously thinking about increasing to 1-1/2".
I still have remaining questions:
1. What size conduit should I use ? Seems like going up to 2" is silly, as it sounds like @tadmaz found it to be plenty even for 3awg wire. Tempted to increase from 1-1/4" to 1-1/2" since I calculate it'll cost me a mere $10 extra, and I do have that underground right-angle fitting.
2. If I switch to THHW (and return the UF-B), can I increase to 35 amps or to 40 amps ? I'm very confused by the relevant NEC table:
http://www.usawire-cable.com/pdfs/nec ampacities.pdf
... and as regarding the wire I'd probably use (if I switch):
https://www.wireandcableyourway.com/THHN-THWN/
Ashful
Minister of Fire
My limited experience, I’ve never regretted going too big, but I’ve often regretted going too small. The regret comes two years from now, when you decide you want to add a 3-way switching circuit (or two) to control the exterior shop/shed lights from the house.
At $10 incremental cost, I’d always favor going at least one or two sizes over minimum required.
At $10 incremental cost, I’d always favor going at least one or two sizes over minimum required.
Makes sense. Plus, since I can get 8awg by the foot, and I only need 80 ft (as opposed to 100ft rolls of 10awg), it's almost as cheap to run 8awg, so I think I'll do that.
Running THHW/THWN, if I go 8awg, the EGC wire only needs to be 10awg, right, and it can be bare uninsulated wire ?
Or use XHHW, which sounds like it's just fine for underground in conduit, and is sold by the foot in 10awg (at wireandcableyourway-dot-com)
if you are going with 8 then it should handle the 40 amp. if your going with LB instead of boxes pull 3 14ga wires in with it for the possible 3 way cuz you won't be able to pull thru LBs after. i'll bet the small pvc box is cheaper than the LB then the only 90 degree bends should be pipe sweeps so future pulls are easy.
I'm not following. Why won't I be able to pull thru my LBs after ? Isn't that what they're designed for ? And whatever I do, I'll have a 90 where the underground line kinks, and a 90 where each end comes up out of the ground.
Once wires are in a conduit it is hard to pull additional wires. Use a metal snake to pull the wires, not rope.
Instead of a 3-way, I decided to put outside motion detecting lights at the garage entrances.
Instead of a 3-way, I decided to put outside motion detecting lights at the garage entrances.
My conduit is grossly oversized, using 1-1/2" for four 10awg XHHW conductor. So I hope for the best. Still better off than I would have been if I'd been able to get the damn ditch 24" deep and used the UF-B. I guess the fallback (if I want to add wires) is to disconnect and pull the existing wires and start over.
Why ? You mean if I need to add wires later ? For the initial, I was going to string old climbing rope thru the PVC as I install it (not the wire, so as not to get PVC dope on the wire insulation), and use that rope to pull the 4 strands of XHHW and a light nylon cord for future work.
Interesting followup, there's some character over at stackexchange who has made this erroneous statement (that you can't splice in an LB), and when I corrected him, well, let's just say he wasn't happy (see last few comments after the one "answer"):
https://diy.stackexchange.com/questions/123384/pulling-wire-through-emt-and-pvc-conduit
His answer was actually quite good, except for that one mistake.
Stackexchange is a weird place: Half the time I ask a question there, I get more bitching and moaning about how I asked the question, or was it in the right forum, that actual helpful responses.
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Multiple reasons. A metal snake (fish tape) will eliminate the need to thread as the pipe is laid down. Rope, especially poly or nylon may get glued? A metal snake stays much more rigid in a pipe for smooth pulls. They are cheap at Harbor Freight. https://www.harborfreight.com/100-ft-fish-tape-3891.html
1.5" conduit is really big for 4 #10s so pulling additional wires may not be an issue with a pull rope already in place. But if you are planning on future updates, then why not get them done now? The issue with pulling additional wires is that they may wrap around (over and under) the existing wires and cinch up. It can be done, but sometimes is a real hassle.
Come to think of it, I think I used metal fish tape (like above) and the chinese finger trap type device to connect the wire to the fish tape.
Ashful
Minister of Fire
When I add additional wiring to the conduit, I always disconnect the original wire bundle, use it to pull the snake back thru, tie in the new wire, and re-pull the entire bundle. My pulls are almost always under 200 feet, so it’s not a big deal, and it keeps everything neat and tidy, soothing my overly anal-rentitive tendencies. Also, even with oversized conduit, pulling a snake and new wire past bends can be a bear, and I worry about the possibility of the snake rubbing one of the existing wires in the bend.
I thought of that, but it seems like it puts a lot of wear and tear on the insulation of the older wires.
Ashful
Minister of Fire
Maybe. But I suspect not nearly as much as running 100+ feet of metal fish tape past a fixed point of existing wire insulation in a swept conduit elbow.
xman23
Minister of Fire
If I remember my industrial wiring. No more than 2, 90's. And pulling around 2 90's is not easy. No splices where you can't access it. I think you are doing LB underground, so no splicing there. Avoid splices, there only potential bad connections.
I would consider pulling some of these. A few pairs of 14 gauge, cable line, cat 5, a multi cable with a number of twisted shielded pairs.
I would consider pulling some of these. A few pairs of 14 gauge, cable line, cat 5, a multi cable with a number of twisted shielded pairs.
Hmm, there's already two 90s, where the risers to the LB boxes on the two buildings (house and shed) come out of the ground. So no 90s allowed in the horizontal run ? Glad I'm using way-too-big conduit then.
I am most definitely NOT using an LB underground. There IS a 90-degree bend underground though. And I'm certainly not intending to splice underground. I will splice NM from the main breaker box to the XHHW from the shed, in the LB on the side of the house (treating it as a junction box and noting that it's easily got enough volume, which volume is clearly marked).
those two 90's are ok leave them and just pull your wires. i think your starting to over engineer the simple job of a circuit thru a pipe. your doing fine with the size pipe you have. i pulled a 430 foot service from the house out to the transformer 4 90 degree bend but only used 3 90's. one bend was sweeped over gradually. 2 inch pipe 3 250 mcm wires. legal with the code book. had to use a truck to pull the copper wires in the pipe and 3 people feeding it. 2 gallons of wire ease. in that pull the owners truck had 17000 miles and tranny got so hot it melted a plastic tranny line connector turned the fluid black and call a hook for that dodge truck. got a backhoe to finish he managed to get 20 feet pulled. to much for the backhoe. the hook arrived we talked him into using his winch. he had his truck on two wheels sideways and broke the 10000 pound tinsle strength rope. thought someone was going to lose a head with steel line coming out at us. backhoe dug so we could hook the rope again and then i hooked up my e350 and pulled the rest of 80 feet til the rope broke again. finished the next day by taking off 1 of the 90's and it just about slid itself in the last 20 feet. long story but that's how 1 90 degree fitting can make it miserable
Wow. That is one service install you'll never forget.
CaptSpiff
Minister of Fire
Oversize your conduit, keep your workers happy.
Oh,.. and don't be cheap with the cable lube, that's what new guys are for.
Pulling problems are one of the leading causes of unscheduled OT.
And Yup, your equipment breakdowns were the result of pulling problems.
One of the few things i remember from electrical school is that 4-90's is the max in a single run. (360 degrees total for all bends)
Assuming you don't count the LB bodies at each end, and do count where the risers to the LB bodies go into the ground, I'll have three 90s and a 45.
xman23
Minister of Fire
Frank,
You start by saying leave those 90. Then your burning up a truck pulling thru your 90. So funny.
i am usually a oversize guy but at that time the cost was big for a reduced rate for buying 500 feet and i did what at the time boston edison use to require and that was use copper underground not aluminum. at that time it was transitioning to aluminum the customer was complaining why the cost of the service was high and the other houses on the street were aluminum i couldn't add on any moreOversize your conduit, keep your workers happy.
Oh,.. and don't be cheap with the cable lube, that's what new guys are for.
Pulling problems are one of the leading causes of unscheduled OT.
And Yup, your equipment breakdowns were the result of pulling problems.
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