Question about UG electrical service conduit to shop building

[TC65023]

I will putting in my 100 Amp electrical service from meter pole to my new shop building before winter. It's about a 250 foot run. I will be using 2 inch PVC conduit. I am thinking about mixing schedule 40 and 80 pipe. Basically using schedule 80 at both vertical exposed risers and at horizontal area where the conduit trench crosses my private gravel service road. All other horizontal conduit in the yard would be schedule 40. Since the schedule 40 is about half the price of schedule 80, this co-mingling of materials saves me about a 100 dollars in material cost.

The conduit will be buried at least 18 inches deep and generally should not be subject to any impact damage from shovels or tilling operations. I will be installing vertical expansion fittings at both risers.

The aluminum feeders will be installed by a qualified electrician at a later date. Do I need to be concerned about water entering the conduit and spilling inside my building since it is considerably lower than the grade at the meter pole location? Since all pipe fittings and joints are sealed and the ends of pipe are connected to enclosures...the only source of water would likely be condensation in a exposed vertical riser, most likely at the meter location. Should I install some sort of a drain to daylight at the lower end of the conduit or is that overkill?

Has anyone else done this? Is there a better way doing this or something I haven't thought of?

 

[slowzuki]

Yes water is a concern, building at work had water backup around a pad mount xformer and ran down the conduit into the panels in the basement shutting down the power for a few days.

I bought the underground rated tech cable and direct buried. It ran inside regular schedule 10 4" PVC under my slab to the meter, then through to my service disconnect. Expensive stuff but its water proof.

 

[955Lincoln]

Is code requiring you to use schedule 40 or better? The reason I ask, there could be another option called DB60 which is half the wall thickness of schedule 40. I'm using 3" DB60 for my 1800' electrical run and 2" for phone and the cost was .62 per foot for 20' sticks of the 3" and I think .51 per foot of the 2" also in 20' lengths. I was going to switch to schedule 40 to cross a gravel road but ended up staying with the DB60 because I feel it's strong enough especially with compacted soil all around it. By code I'm also using schedule 80 for the riser at the building.

People who lay conduit for a living all swear that no matter how careful you are there will be water seeping into the conduits. Maybe they underestimate the power and determination of picky homeowners. 500' of my run is through wet saturated soil and 3 creeks so this portion will always be in wet conditions. The creeks are my "low points" so I couldn't really put any drain holes there. I hope the power company will blow or run a mandrel through before running the wire so I can see if all of my joints are waterproof. Somehow I doubt it though. The wire is underground rated and can be totally submerged in water but I would rather have it in dry conduit.

 

[TC65023]

955Lincoln: the schedule 80 conduit is the utility company's requirement for exposed vertical risers. My horizontal conduit run in thru hard pan soil conditions (rocky) so I wanted at least some impact protection so I selected schedule 40 because of the thicker walls and the 40 cent per foot local cost of the material. I live in a rural county which has no adopted codes or enforcement officer. Schedule 80 is 80 cents a foot here, so I will use it only where required by the utility and under a road.

I guess I could alleviate any possible build-up of moisture at the lowest point (building entry) by drilling a hole in the conduit and draining to bed of gravel around and under the pipe.

 

[grsthegreat]

IF you want to enclose the wire in pipe, The National Electric Code requires minimum sch40 pipe (if you use PVC pipe) for all underground work and sched 80 for anything above ground. There are other kinds of pipe, such as fiberglass, but for this discussion the OP was wanting PVC pipe. What i like to do, and what most contractors here in north Idaho do, is we run whats called URD direct burial wire INSIDE of the conduit. This wire could care less if its totally covered in water or dry. The conduit just gives it more protection.

That being said, pulling 250 feet of it AFTER the pipe was already laid can be an issue, especially if too many bends/radius's are used. What I usually do, as it saves the homeowner lots of $$$$, is to install the wire in the conduit AS THE PIPE IS BEING LAID.

I will stretch out the 250 foot run of 4/0 URD wire (and a ground wire if its being fed from an existing panel) first. then ill slip on 20' runs of pipe one at a time and slide it up to the 1/2 way point. then add one more stick at a time till i get to one end. Then do the same thing on the other end.

Doing this allows a single man to install this entire run. If i had to pull the wire thru 250 feet of conduit, id need some help, and probably a block and tackle, some 3/8" pull rope and 2 men and a boy to pull plus 1-2 guy feeding and pushing the wires. Ive been doing this for over 30 years, and it NEVER pulls easy. Now if your electrician has a nice winch and mandrel system.,.... cool. But i don't. I probably couldn't even get it to most of my remote jobsities if i did have one.

As for drains in the pipe. I have NEVER seen anyone put a drain or drain hole in a conduit pipe. I have also never seen an underground conduit that is dry. they always have standing water in them. All wires that are rated for underground use will have a "w" rating on them that allows use in a wet environment. URD cablew is a 3 wire twisted wire that can actually be laid underground without any conduit at all.

As far as depth of trench. 18" to TOP of pipe on areas not exposed to traffic for piped wires and 24" where subjected to traffic . this is for residential traffic.

 

[BeezFun]

I installed the conduit from our pole to my new meter location when I did a remodel on our house. The power company knocked off $1500 of the price for me to install the conduit. They would have direct buried the cable without using conduit, but we'd had two failures from rocks penetrating the line during the previous 30 years, so I wanted it protected. They required 3" minimum PVC, but it was 200A service and about 350' so it was probably a good bit heavier cable than you require. They just asked for schedule 40 everywhere, I put it 36" deep, can't remember if that was a requirement. The riser at the meter end goes right into the bottom of the meter enclosure. At the street end I left the riser and elbow loose to make it easier for them to do the pull through a straight section. They took the riser and elbow off, pulled the cable, then slid the riser on after the pull was done. They cut the riser off below grade, then just threw dirt in the hole to cover it up. The line goes up into the pedestal. I was required to provide a cable for them to do the pull, I used a shop vac at one end and attached a small nylon line to a plastic shopping bag and sucked it through. Used that to pull through a heavier cable.

As for drainage I assume all the cable they're using is rated for underwater, so I wouldn't worry about the cable. If you're worried about water actually coming up the riser and into your building, I'd use one section up near the house with holes in the bottom for drainage and backfill it with washed rock. I wouldn't put a dry well next to your foundation if you really think there's going to be much water.

 

[grsthegreat]

Most utility companies REQUIRE the runs from a pole to a main meter panel to be 36" below grade. This has been the norm in 5 states that i have worked. They also want large 24" diameter radisus used and they always like 3" conduits if they have to PULL the wires in later. Over say 200', we usually upsize the wire size from 4/0 to a 250MCM wire. Sometimes even larger for longert runs. My shop is 300 feet from the servise, i used 3" conduit and 350MCM feeder wires for 200 amps.

 

[dstig1]

As for drains in the pipe. I have NEVER seen anyone put a drain or drain hole in a conduit pipe.

Inspector required it on a former house of mine I re-did the electrical on a few years back. Meter was on the wall, fed down the outside wall into the panel in the basement. The pull ell that pointed into the house was the low point and he required a weep hole drilled in the bottom of it. He didn't fail the job for it, just told me to take care of it so I did. Made sense to me.

 

[grsthegreat]

Inspector required it on a former house of mine I re-did the electrical on a few years back. Meter was on the wall, fed down the outside wall into the panel in the basement. The pull ell that pointed into the house was the low point and he required a weep hole drilled in the bottom of it. He didn't fail the job for it, just told me to take care of it so I did. Made sense to me.

Oh, i don't doubt you at all, i just have never seen it myself. Does make sense if you think about it. It wont hurt anything

 

[955Lincoln]

and the 40 cent per foot local cost of the material

Wow! I wish I lived in your area. I have never heard of such a low price. Are you sure that is the grey colored electrical grade? The best price I could find was about 3 times more per foot.