Running underground electric to shop

[Keith Nordyke]

I posted on this a week or two ago and now have another question. Currently have aerial triplex to shop but need to run underground. Have a 100 amp panel in shop. Run from house will be about 180 feet. The previous question was related to awg and the consensus was that #2 was required. I agree. Before I go to the electrical supply house to buy cable and otherwise suffer sticker shock, I'd like thoughts on direct burial versus running schedule 40 and pulling the cable. It may be cheaper to use conduit rather than UF. Comments? Thoughts? BTW, when searching the internet and trying to locate prices, what should I call these things: UF? SE? What is the appropriate format to google? UF 2/3? Thanks

[Rollie Meyers]

I posted on this a week or two ago and now have another question. Currently have aerial triplex to shop but need to run underground. Have a 100 amp panel in shop. Run from house will be about 180 feet. The previous question was related to awg and the consensus was that #2 was required. I agree. Before I go to the electrical supply house to buy cable and otherwise suffer sticker shock, I'd like thoughts on direct burial versus running schedule 40 and pulling the cable. It may be cheaper to use conduit rather than UF. Comments? Thoughts? BTW, when searching the internet and trying to locate prices, what should I call these things: UF? SE? What is the appropriate format to google? UF 2/3? Thanks

Are you using copper or aluminum? #2 AL is only good for 90A, conduit is cheap insurance over a direct burial cable & oversizing the pipe will help matters 2" SCH 40 PVC is my suggestion, buried 18" where not subject to vehicular traffic & 24" where it is., & lastly a USE type cable for direct burial, or if in conduit a conductor suitable for wet locations is required.

[Keith Nordyke]

I intend to use copper. I only have one "crossing" of a drain from washer to sewer main and plan to put the conduit (if not direct burial) at least 24". What am I looking for if NOT direct burial and run in schedule 40? What am I trying to google? Thanks

[Roger Frazee]

You can throw out uf they don't make it in #2..:)

BTW.... UF is underground feeder direct burial rated,... USE is underground service entrance direct burial or conduit,... THWN is nylon coated polyvinyl copper wire for conduit wet or dry locations (not direct burial)

You didn't say whether you have chosen aluminum or copper .... but #2 tells me you want to use copper soooo for use in conduit you want thwn or thwn-2 it will also likely be rated thhn and rhw and rhh. Your ground wire can be #6.

Direct bury copper wire methods are not readily availabe at the borg other than UF-B cable. Supply houses can get you copper USE direct burial or conduit or direct bury 600V power cable called tc cable.

Conduit is IMO easy to do and is well forth any small added expense.

oops.... I see you have replied to Rollie that you want to use copper

[Heath Brandenburg]

I'll provide another vote for running conduit. While I don't have any experience with underground power, my experience in the cable industry says that conduit is almost always preferred over direct bury: it is easier to maintain/replace/upgrade and harder to damage.

[Phillip Bogle]

I agree with Rollie. I have run three circuits and always use direct burial cable inside PVC (it is the gray plastic). I think I used 1/5" or 2", it depends on the amp size of the circuit. At least here it does. I would be inclined to go larger incase you want to increase the circuit size. Just pull new cable and no digging. The code required a 2" PVC weather tight conduit. There is a specific type for that purpose. I am not very helpful since I can not remember the schedule or specs, and our area may be different from yours. The direct bury was OK on two of the circuits, but the better insurance of not digging through the line was worth the few dollars of the PVC. I went deeper than 18".

[Michael Wetzel]

Use conduit since it gives you a second level of protection above the wire insulation. Plus a wire failure means pulling new wire and not retrenching.

[Robert Parrish]

I have 2 underground cables to my garage (300') and they are both in conduit. One is for 100 amp power and the other is for my whole house generator.

[Marshall Border]

I buried mine 24" deep and I used 3 wires of #2-0 tri-spex Aluminum { forgive my spelling } 150' from the house { used a 125 amp breaker box }. Had a Master Electrian tell me that it would do the job and this way less work messing with the PVC pipe.or conduit...the master Electrian made the final hook-up to me..and city inspectorsaid it was a fine job.....this is my second shop I build so this time I wire it heavy-er....Marshall.......;)

[Bob Borzelleri]

60 feet and ran conduit. It was a slam dunk decision for me. No downsides to conduit.

[Rich Aldrich]

I have 100 amp service going to my pole building and another that goes from the pole building to the shop. The runs are 100 ft and 70 ft. It is underground and not in conduit. These were installed in 1991 and I have had no issues. The wire is copper and was used cable from a pump application in the papermill where I work. It is rated for underground use.

If I did it again, I would put it in conduit just for safety. My area is all sand, but there are small rocks. Since I drive over both cables, frost can shift rocks around and possibly into the cable. I was careful to tyr to make sure no rocks were in the sand around the cable, but I could have easily missed one.

[Scott T Smith]

If I did it again, I would put it in conduit just for safety. My area is all sand, but there are small rocks. Since I drive over both cables, frost can shift rocks around and possibly into the cable. I was careful to tyr to make sure no rocks were in the sand around the cable, but I could have easily missed one.


I had this happen to me on some cable that I burried several years ago on my farn. It was some aluminum tri-plex direct bury cable, and when backfilling a small rock got up against the jacket in an area with a lot of heavy vehicle traffic above it. Several years later my power bills started going up, and then I lost one leg of the circuit to that particular barn. Turns out that the rock slowly damaged the jacket, and eventually water started seeping in. Not enough to trip the breaker, but enough to cause the loss of power and eventually the alumimun corroded through.

The last time that I ran a service to a barn I installed 4/0 aluminum tri-plex inside of a 3" conduit. No rocks, and easy for future upgrades.

[Bill Arnold]

... but need to run underground. Have a 100 amp panel in shop. Run from house will be about 180 feet. ...

Your situation is identical to mine. I did all of the internal wiring of my shop but hired a local electrician to do the underground run from the distribution panel to the subpanel in my shop. To handle the load, he ran two #2(hots), one #3(neutral) and one #8(ground) - all is THWN. I've had no issue with voltage drop even when the AC is on, DC is running, tablesaw is on, air compressor kicks in and all the lights are on.

[Don Jarvie]

A couple of thoughts...

1. Definetly run conduit

2. Do you need 100 amp in the shop? I know more is better but if you can manage on 60 amp which should be plently for a 1 man shop it can lower you cost.

I paid 2.50 a foot for 6/3 and ran it in 1 1/2 conduit. I bought 100 ft so it was 250 for the wire. Bigger wire more money..

If I have the heater (21a), TS (18) and DC (10) = Max amps at once plus lights I don't get close to 60.

Something to think about.

[keith ouellette]

I did the same length of run you are talking about and did it in conduit because I like the safety of a nice 2" conduit.

At the time I was over worried about resistance build up and was advised to use 1/0 which was really to big. Even if I ever came close to using 100 amp (I don't think I ever will now) I wouldn't need it but am still glad its there.

One thing I did that might help you is this.

I dug my trench

Gathered all my conduit

Laid the bundle of cable next to the trench with the appropriate amount set to go into the box in the shop

then I slid the conduit over the cable piece by piece and cemented each piece in turn being careful not to slop any on the cables.

placed the whole thing in the trench.

Very very quick and easy. I did it all myself.

[Randy Rizzo]

Conduit, makes for additions to electrical easier and you'll always find something you'll want to add in the future. We ran 2" for the electrical service and 2 additional 1" and a 4th conduit 1 1/2" for water poly pipe. Since initial installation we've pulled wire for outside lights controlled from the house, added some CAT5 cable for a security camera, and telephone lines.

[Rollie Meyers]

I did the same length of run you are talking about and did it in conduit because I like the safety of a nice 2" conduit.

At the time I was over worried about resistance build up and was advised to use 1/0 which was really to big. Even if I ever came close to using 100 amp (I don't think I ever will now) I wouldn't need it but am still glad its there.

One thing I did that might help you is this.

I dug my trench

Gathered all my conduit

Laid the bundle of cable next to the trench with the appropriate amount set to go into the box in the shop

then I slid the conduit over the cable piece by piece and cemented each piece in turn being careful not to slop any on the cables.

placed the whole thing in the trench.

Very very quick and easy. I did it all myself.

That is not a code compliant method, the entire conduit run needs to be installed & then the conductors pullled in, see 2005 NEC 300.18(A) this section has been largely unchanged for years with the exception of short sections being used for physical protection from damage being added in 2005 . A "short" section is in most cases is defined as 24" or less.