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.

 

[hr3]

Sorry Mark,, your right and the most important thing he can do is check with his local utility and code office to see what they require,,

 

[Red55]

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.

Great Idea! I used some of that blue (or pink) foam stile sealer 6" above our sewer injection line. 12 yrs later when we had a slight leak at a failed coupling it was a life saver cause of the amount of hand digging (raw soil ) it saved. -Ed

 

[Illini22]

4/0 phases and a 2/0 nuetral al. will carry 200 amps all day long. I personally like direct bury I did it for 21 years at the major electric utility in chicago, the last 5 at a public utility we put everything in pipe. You can use 3" for up to 350 aluminum with no problem. To me its easier to fix direct bury than pullying200 feet of wire out of a pipe to fix You just need a fault finder to find bad spot and dig it up splice and shrink tube it, in the mean time you still have power in your building from the other phase, of course I've only fixed a few thousand faults.

 

[slaveToHorses]

Good point about fixing it. Although I haven't ever had a UG service fail inside a conduit before. I would think the chances of a failure inside a sealed conduit to be pretty dang slim. But I don't have your experience either.

I did 3 on my property. One was before the meter, 150' from pole to house. The local power co said to use 2" electrical PVC.

I did the rag tied to a rope and pulled through with a shop vac trick to install the pull rope. I also installed a smaller conduit for the phone and cable co.

 

[Lineman North Florida]

All cable be it secondary or primary has a reasonable life expectancy, being direct buried shortens that life expectancy in certain soils, an earlier poster stated his personal preferance to direct bury and it certainly is cheaper and easier, but you as a homeowner probably don't have access to a fault locator and will have to pay someone to come locate the fault and then your yard has to be dug up to fix it, not to mention you will need splices to repair the wire and a special tool to crimp the splices etc etc, basically it is not a homeowner project, I spend a lot of time finding burnouts on my friends barn services cowlot lights etc that I tried to get them to install in pipe years ago when they did these projects. Schedule 40 gray electrical conduit is cheap insurance to keep from having to deal with these issues 20 years down the road and if the wire outlast's you your kids will say dad was a smart man and thank you for your forethought, what ever you decide burying in pipe is the smartest thing to do. I am an electrical lineman by trade, mostly overhead but a little in underground and this advice is just what I have learned over the past 24 years, I hope it helps, good luck.

 

[SuperCobra]

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.

Some more unsolicited advice:

I thought for sure that I could save money renting a trencher, buying the wire, and doing all of it myself - so I didn't even bother comparing. Just had to have the electric coop guy come hook it up to the meter. When he came out I found out they would have done the whole thing for about half of what it cost me - bulk wire prices, etc.

 

[DELInstallations]

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.

We have to mark all buried utilities like that in my area

 

[deere5105]

I work for an electric co-op in the design end. We made a swap about seven years ago to putting everything in conduit. 3" Sch. 40 electrical PVC is the standard. Some applications require different size conduit, but 90% is covered by 3". We have a website that you can go to that gives guides on the conduit installation and shows what we require of our consumers. The site is Pearl River Valley Electric Power Association. Your local provider may also have something like this. I do not recommend ever direct burying the wire. Conduit provides protection not only to the wire, but also to anyone that may inadvertantly dig into it. Someone mentioned the marking tape which is also a good idea. I have seen some electricians use a tape that has some sort of strip on it that can be detected by a metal detector. Someone also mentioned the difficult task of locating a fault in a direct buried cable. We have special tools for this purpose and even using them it is still a pain. Sounds like you have already decided to go the conduit route. You won't regret it.

 

[Believer]

Deere5105,
I couldn't find the instructions at the web site provided. If you get back to this thread, could you tell me where to navigate? Thanks all for great help.

 

[deere5105]

Believer,
The information is a little hard to find. Go to the site and click on new service, then there is a place to click for a link to temporary and permanent service specifications. I am going to attempt to past a link to it here: http://www.prvepa.com/forms.htmlk Hope this helps. Again I would recommend contacting the local utility to see if they have specific requirements. We typically meet our consumers on site and go over the route we want them to take, the details around the installation and any site specific issues. One other thing I failed to metion is that just as someone else mentioned, it is rare that a private homeowner can come out ahead by doing it himself. We reduce the cost by several dollars per foot if they install the conduit, but by the time you get a machine and the material it is usually not much savings to do it yourself. I have dealt with several situations where someone tried to do it themselves and I had to turn them down and in some of the situations they chose to scrap their attempt and let us come put it in. We require an inspection before backfilling and one guy put in over 900' over the weekend. By the time we got to inspect it on Monday it had rained and floated his pipe up. He never finished the installation and wound up selling the property. The next owner just paid us to run it.

Deere5105