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  1. #1
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    Default Service Cable to Outbuilding

    I've inherited a situation in which an outbuilding I'd like to electrify has conduit run to it, but no service wire pulled.

    The conduit is 1-1/4" schedule 40 PVC, buried 24" deep over an approx. 250' straight run.

    I'd like to maximize the power available to the outbuilding. What size and type of wire could I feasibly run? Any tips on fishing a cable across this distance would be much appreciated.

    Thanks!

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    I think you are limited to 4 copper size 1 wires. (Red, black, ground,neutral) with that you should expect a <5% voltage drop at 75 amps. To pull wire, tie a wad of cloth to string line and use a vacuum cleaner on other end to suck string through. Then use string to pull poly propylene rope through and then use rope to pull wire through. Since you are maximizing wire size use some wire pulling lube. Pulling maximin size wire this distance needs a helper. He pulls and you keep wire tangle free, lubed and push it into conduit as he pulls. Set up your cell phones on speaker so you can synchronize your efforts.

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    1-1/4 isn't very big for that length of run. Obviously you would need to check with b&s for your local codes, but #4 is probably the biggest you can pull. Fish tape will never make it that far, you'll want to use a 1/4 nylon rope. What I do, take a roll of masons line. Tie a nylon washer to one end and drop it into the conduit. Attach a shop vac to the other end of the conduit and suck it through. Then use the mason line to pull the nylon rope through.

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    Did you run the conduit? Are the IDs of the sweeps (90s) deburred? Might make a difference on the size of wire you can pull. If some one else did a hack job with plumbing 90s you may have trouble pulling 10 gauge.

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    So here's the number of conductors from Ugly's Electrical References: 1 1/4" PVC Sch 40, I'm assuming THHN 16-#8 11-#6 7-#4 6-#3 5-#2 3-#1. The size of the wire is going to be dependent on how much current you need at the far end, also single phase or 3 phase. Lets assume single phase, #2 will get you 90 amps 240v with a little more than 3% voltage drop.I understand they use a vacuum to suck a "birdy" through the conduit with a pull string attached. They sell electrical birdies but I was told plastic shopping bags work too.

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    If it isn't a straight run, the code only allows 360 degrees of turns(four 90 degree elbows, for example) between pull points in conduit.

    Make sure you use lots of cable lube. It will make a world of difference.

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    If the conduit is too small for your power needs maybe it can be used to run alarm wires, tv, floodlights etc after you install a bigger one next to it.
    You can buy big cable on craig's list at good prices. also used breaker panels on the bay. depends on if your inspector will allow used stuff or not.
    Bill

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    Quote Originally Posted by Larry Dickman View Post
    1-1/4 isn't very big for that length of run.
    Point. Not JUST about Ohmic losses over the run. Ampacity must be de-rated for tight conduit. Hard to shed heat FROM those losses.

    One Old Day Job, they had to dig up the carpark when the service cable melted its jacketing plastic into the plastic conduit from sustained low-level overload. Breakers hadn't tripped. Bank account, rather!

    If you need serious power, might be best to bite the bullet early-on and run a fresh trench with larger conduit than you will EVER need.

    Cheapest part of the job, the conduit, as it gives you more future-proofing on always-expensive (and getting more so) Copper wire, and possible UPGRADE of the wire you can still pull out, recycle, and replace with larger at low hassle, later-on.

    2CW

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    Single or 3 phase ?

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    The power co used underground cable here (no conduit required). I had a separate 200 amp (single phase) service added to the shop. They (power co) put a ground-mounted junction box near the existing service inlet (existing 200 amp), and used underground cable to the shop (probably 75+'); the only conduit required was from the underground cable to the meter-box. No change was made to the existing service cables or transformer. There wasn't any charge at the time either.

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    http://conduitfillcalculator.com/
    http://www.paigewire.com/pumpWireCalc.aspx
    http://www.codebookcity.com/codearti...onduitfill.htm

    for 3 phase delta you need 4 strands of 2 AWG, that will be a 32% conduit fill. (you might be able to squeeze in the 5the for Y) That is probably the max you can do. If you want to save on the wire and go with alu. wires you have to go down to 60 amps., copper will give you 90 amps. If you do one phase you run just 3 wires instead of 4 or 5 so you can go up to 1/0 AWG wire that will give you 100 amps with alu wire or 125 amps with copper.

    dee
    ;-D

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    Quote Originally Posted by car2 View Post
    There wasn't any charge at the time either.
    Powercos USED to have some sweet deals - when they saw it to THEIR advantage. I recall a mere $80 fee to convert a Bethel Park, PA residence from about 60 feet of overhead Al to all-underground Cu.

    Next go, cold-start to a newly constructed home, Cu from the get go, it was an over $800 premium fee. And that was early 1970's. I'm not even gonna ASK for this place. Al & 200 A undergrond to begin with hasn't set a foot wrong in scores of years. Al is 100% THEIR side of the panel, so I don't care.

    When it is DIY, and 100% your own dime, though, the conduit pays back with flexibilty of what you want IN it, now, or at some future date.

    Side note, but in the era Hong Kong had set the goal of being Earth's most intensively digital networked city, (ISTR Iceland was the main competition?) folks got SOOO pissed-off at streets and sidewalks being dug-up 13 months a year the Government passed laws REQUIRING conduit-holders to share - then capped the lease fees for it. We were being undermined with metric equivalent of 3+ inch conduits, each with one tiny single-mode optical fibre or hybrid coax/fibre run down it. Worse, the krews just HAD get playful and cut water lines and gas lines every few hundred feet as they went. Must have been a betting pool on that, as often as they did it.

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    Many thanks for the feedback thus far. To answer a couple of the questions posed:

    1. Single phase

    2. There is one 90-deg sweep at the end of the line where it turns into the barn. I'd already resigned myself to digging this up so I could pull the wire in a long straight line before hand-feeding it through the 90 and into the barn. From what I'm reading, however, that may serve only to complicate the job.

    3. The local electrician I've consulted says "#2 aluminum" is all I can use. Not sure how to interpret that. I'd like to derive the most power I can from the trench I've inherited--digging a new trench is not an option--but clearly don't want to run the risk of melting an oversized wire to the conduit, as one of you pointed out. Yikes.

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    Quote Originally Posted by hannahbsturm View Post
    Many thanks for the feedback thus far. To answer a couple of the questions posed:

    1. Single phase

    2. There is one 90-deg sweep at the end of the line where it turns into the barn. I'd already resigned myself to digging this up so I could pull the wire in a long straight line before hand-feeding it through the 90 and into the barn. From what I'm reading, however, that may serve only to complicate the job.

    3. The local electrician I've consulted says "#2 aluminum" is all I can use. Not sure how to interpret that. I'd like to derive the most power I can from the trench I've inherited--digging a new trench is not an option--but clearly don't want to run the risk of melting an oversized wire to the conduit, as one of you pointed out. Yikes.
    Not sure I am code-current, but Virginia, Aluminium isn't even allowed for a residential subscriber's use past the initial entrance. Powerco or industrial, only.

    The proper alloy, proper prep, terminations, protective paste chemistry, it can be 40+ year trouble-free. Powering this PC as we speak. As far as the panel, anyway. All Cu thereafter.

    OUR side of the entrance, we Chikn's, nor even our "residential grade " hired sparks are not trusted to DO that to Powerco standards.

    I'm good with that.

    I pulled four "grandfathered" Al runs out of this house early-on - just on general principle. Wise move, as every one had also already gone problematic and was headed for worse.

    Al needs to be done professionally, and to a very high standard, better-yet, not at all. Powercos understand it and manage it well. Good on 'em. Not enough Copper to go around, and Al is far cheaper even if there was.

    OUR expertise? "Spotty, at best." Seldom worth the risks.

    IF.. that sparks could not show me chapter and verse as to WHY I could not have THHW Copper instead of Al "service entrance" premade? I'd be having a coffee with head of Code Enforcement over at the County HQ, same week.


    2CW

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    Quote Originally Posted by hannahbsturm View Post
    . I'd like to derive the most power I can from the trench I've inherited--digging a new trench is not an option--but clearly don't want to run the risk of melting an oversized wire to the conduit, as one of you pointed out. Yikes.
    It may be entirely possible to pull a 2" pipe through your existing hole without digging a new trench. Worth looking into.

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    Quote Originally Posted by Larry Dickman View Post
    It may be entirely possible to pull a 2" pipe through your existing hole without digging a new trench. Worth looking into.
    OP has conduit. That could work.

    "Direct burial" others have?

    Taken offline, cold, the old cable COULD guide a mole I suppose?

    There are contractors about as can solve all sorts of formerly "impossible" challenges. Not always at huge costs, either.
    Last edited by thermite; 04-11-2018 at 06:18 PM.

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    Quote Originally Posted by thermite View Post
    "Direct burial" he has?

    Taken offline, cold, it COULD guide a mole I suppose?

    There are contractors about as can solve all sorts of formerly "impossible" challenges. Not always at huge costs, either.
    As an aside, I did a bit of work a few years ago on a project where they were trying to re-use the "exoskeletons" of existing underground rigid cabling systems to route new fiber-optic because of the cost of adding utilities in urban areas. When I was in Beaufort, they were tunneling a new underground conduit under the bridge/road with one of those big diesel rigs parked on cribbing in the marsh, and under the road; I noticed when walking across the bridge, they had some light guage wire taped along the handrail across the bridge; must have been an antenna/transducer to guide the drill.

    Yea, the "free" deal from Progress Energy (8+ years ago) on the free extra-service pull probably wouldn't happen with the Duke Energy takeover. But there's no way not to have the power company do it, can't use the existing box to pull additional 200 amps, it has to be spliced into the incoming service requiring the power co. (well nothing is impossible if one wants to risk being electrocuted, but the power company would also promptly turn off your power when they found out). This is all aluminum underground cable to the meter lugged connections, 2' underground. Apparently now it's a moot point, as I understand it, with yuppification and carpetbaggers having taken over the county and city bureaucracies, they will not pull a second metered service on a single lot any longer anywhere in the county (not to mention other fees and permits have skyrocketed in number and cost). Cheers

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    Search "pipe bursting" to see how they can pull a rope in your existing conduit and burst it so they pull a bigger one inside.
    Bill D.

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    Quote Originally Posted by hannahbsturm View Post
    Many thanks for the feedback thus far. To answer a couple of the questions posed:

    1. Single phase

    2. There is one 90-deg sweep at the end of the line where it turns into the barn. I'd already resigned myself to digging this up so I could pull the wire in a long straight line before hand-feeding it through the 90 and into the barn. From what I'm reading, however, that may serve only to complicate the job.

    3. The local electrician I've consulted says "#2 aluminum" is all I can use. Not sure how to interpret that. I'd like to derive the most power I can from the trench I've inherited--digging a new trench is not an option--but clearly don't want to run the risk of melting an oversized wire to the conduit, as one of you pointed out. Yikes.
    No possible way that Al is ALL you can RUN.

    It might be all you can GET, easily.

    The other question is whether this is a second service, or a run off an existing box. If it is a "service", then you might have to use particular cables, although in conduit, you do not use cable. If direct buried, it would be a variety of 'SE" cable, which typically is available as anything you want so long as it is aluminum.

    If it is a run off a box in another building, then it should, if you can pay for it, be perfectly OK as copper, so long as it is a suitable insulation type, since it is assumed that the buried conduit will fill with water.

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    If your sparky was serious about the "aluminum only" comment, you need to find a new electrician. That's absolute BS. If you want to maximize your circuit capacity, use copper THHN or THWN.

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