Underground Service Question

[Believer]

I have about 200 ft of underground entrance conductor to run. I've been told to put even direct bury cable in a conduit so rocks don't pinch it. What are economical conduit choices? I'll be digging a trench with a backhoe. Thanks.

 

[Mark_in_NH]

First I would check with your local utility and or building code officer to see what if anything particular they may require.
I would use at least 3" PVC, the gray stuff. 4" would be more appropriate. I would also run seperate conduits for all utilitys ie. power, telephone, cable. Tele & cable could drop down to 1.5" - 2" and make sure you place a pull rope of some kind in each conduit as you install them. It makes the job of pulling wires alot easier when the time comes.
Personally I would lay my conduits in a good bed of clean sand and then cover them with even more sand before I backfilled with whatever you dug out.
My Father was a master electriction and he was a stickler for "this is not the time to do a half a** job".

 

[theboman]

As Mark mentioned run a seperate conduit for cable/phone etc. and leave a small nylon rope running end to end. Whenever you need to pull a wire just tape it to the rope, but remember to pull another rope as you pull the cable so you have a rope in the conduit for the next time.

I used direct bury cable on my old mobile home but I did put it in conduit for added protection. It wasn't rock so much as there were a lot of springs in the area and figured it would keep the cable dry.

IMHO when working with conduit anytime you have a choice on size go at least one size bigger.

 

[dex3361]

Also remember to keep your bends to at no more than 360 degrees total. For example 4- 90 degree ells are 360 degrees. If you exceed this you will not be able to pull in the cable or pull it out if the need ever arises. I would size the conduit by the NEC (National Electrical Code) and then go 1 size larger(at a minumum).

 

[DELInstallations]

As Mark mentioned run a seperate conduit for cable/phone etc. and leave a small nylon rope running end to end. Whenever you need to pull a wire just tape it to the rope, but remember to pull another rope as you pull the cable so you have a rope in the conduit for the next time.

I used direct bury cable on my old mobile home but I did put it in conduit for added protection. It wasn't rock so much as there were a lot of springs in the area and figured it would keep the cable dry.

IMHO when working with conduit anytime you have a choice on size go at least one size bigger.

The one problem with pulling like that is eventually the rope and cables all wrap around each other, not good. They also tend to "burn" each other unless you use tons of lube.

I wouldn't worry about the string from the beginning. As long as you glue and the joints seal properly, a plastic bag and vacuum work wonders and are a heck of a lot faster.

If it's a building to building pull, always put an extra conduit, even if you have a LV and HV conduit. Cheap insurance.

Pipe is cheap. Even if you direct bury, in my area we have to worry about frost heaves which tend to make rocks work their way to the cables.

And while the code says you can put up to 4 90's in the pipe, I'd avoid at all costs, even if you have to put slight bends or flexing the pipe, each bend makes it harder to pull wires through.

Conduit is the same irregardless unless you start moving towards flex, which my inspectors don't like.

 

[skipmarcy]

Our electric co-op here requires 3" pvc, sch 40 is OK except going under a driveway, has to be sch 80 there and the sweeps coming up out of the ground at each end have to be sch 80. The top of the conduit in the ditch has to be a minimum of 30" below grade and the sweeps at each end have 6 or 8, 1/4" holes drilled in the bottoms. The ditch has to have several inches deep of gravel at the ends where the sweeps are for drainage. A 1/4" rope inside for pulling their larger rope thru. I know they use aluminum wire here for 200a service but am not sure of the gauge. They only guarantee proper voltage to the meter up to 150' from the transformer pole. They also have to inspect the conduit installation before you fill the ditch back in so I'd be sure to check with whoever controls this stuff in your area. If you have to buy sch 80 conduit, be sure and shop around, when I put mine in here 3 years ago Lowe's was getting $55 a stick for it, I got it at Home Depot for about $20 a stick. The price on the sweeps was about the same at both places.

 

[hr3]

Wow guys... all the infomation you have is that his trench is going to be 200' long...you can't size pipe by lenght,,He might be putting in a 1000amp 3phase or just a 100a single... All he wanted to know is what type pipe.. The answer I would hope would be Sch. 40 electrical conduit..

 

[Mark_in_NH]

Wow guys... all the infomation you have is that his trench is going to be 200' long...you can't size pipe by lenght,,He might be putting in a 1000amp 3phase or just a 100a single... All he wanted to know is what type pipe.. The answer I would hope would be Sch. 40 electrical conduit..

I believe many of us mentioned what type of pipe to use. Several of us also offered some helpful suggestions and advice based on knowledge.
kinda what this website is all about.

 

[Believer]

Thanks. I'm getting a 200A meter base and disconnect on the transformer pole THEN running 200' maybe 150' to the house. No permits are required.

 

[Transit]

Lots of good advice, missed something. When closing the trench, run a marker tape a foot over the conduit in the trench. If anyone ever digs in that area they'll pull the tape up before hitting the conduit and take pictures of the trench for reference.