What's new
What's new

Service Cable to Outbuilding

hannahbsturm

Plastic
Joined
May 1, 2016
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!
 
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.
 
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.
 
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.
 
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.
 
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.
 
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
 
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
 
http://conduitfillcalculator.com/
http://www.paigewire.com/pumpWireCalc.aspx
http://www.codebookcity.com/codearticles/nec/conduitfill.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
 
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.
 
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.
 
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
 
. 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.
 
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:
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.
 
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.
 
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.

250' long by 2' down, a ditch witch will be cheaper....no need for "arthroscopic surgery" here.
 
I know you don't want to dig a new trench but trenching is so easy it is not even worth trying to fuss around trying to do something with that 1 1/4".

I just recently ran an underground cable to an outbuilding. I used 2" conduit and pulled 4/0 service wire through it. It was direct burial but this way it gives me a margin of peace of mind in case we ever dig in the vicinity. Went 2' deep and a couple of nice gentle sweeps and let the electrician fight it at the ends for the final hook up. This way I have 200 amps of single phase power. Not a lot I grant you, but we are able to make it work without buring up too much stuff :)
 








 
Back
Top