Non-UL PVC conduit and thoughts on backfills?

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fastline

Senior Member
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midwest usa
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Engineer
I will start by saying this is for my own facility and it will never be inspected. I lost count of how many times we have run sch40 white pressure pipe underground and UL gray conduit sweeps and uprights. Most of this was for either low voltage or 120V/1P applications.

Unless someone has some stories, I am inclined to proceed.

I will need several conduits. 1 for 120/240, 200A, another for 480/177, and probably a couple spares because I do that. What I am trying to brainstorm here is backfill. All these conduits will be under a rock driveway, subject to high wheel loads. While I don't expect my electrical conduits to ever be an issue, I also have water/sewer pipe going in and want to 'standardize' the backfills.

We have done many different projects with different backfills, from native soils, to BD2, sands, CLSM, even concrete. The main concern or thought is rework if ever needed. Concrete is just a no! CLSM has to be ordered at very low strength and is much more expensive! I am inclined to use a sand type backfill but I need to ensure it will survive. Any good or bad experiences along these lines that we can apply to this design?
 
CLSM is cheaper than regular concrete, and the cost savings are there when you account for the man hours with a tamp.
Personally, I like CLSM. It’s so much easier than anything else I have found to use.
 
acin said:
Can i ask what CLSM is?
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Flowable fill

“controlled low strength material”
Basically a real low strength(1200) concrete with no larger aggregate. And wet so it’s basically self leveling..
 
Well, we call it flowable fill around here but I realize CLSM is the 'correct' term.

Regardless, at least around here, it is quite expensive! concrete guys get about 20% less than concrete for it! and I will probably need 10yds of it! Has anyone seen any actual pipe failures? I suspect the water pipes will show me issues before electrics will.

Only time I have ever actually seen a failure was our fresh 24" golfcourse water lines and 2" pipe. They were just native fill with a trench compactor every 1ft. Continuous dump truck traffic took a couple of them out, and always right on a fitting or 90*....
 
I always cringe when someone either uses or proposes to to use white PVC water pipe for underground electrical, when digging the pipe color is the only way to tell what it is & if someone choose to use gray for water, & white for electrical there can be problems.

Many years ago was repairing a sprinkler & there was a bundle of white PVC pipe & 2 of them were in my way, so decided to cut them out of my way then repair them after the first one was repaired, turned out someone pulled a 14/2 UF cable in one of them, thankfully not live.
 
norcal said:
I always cringe when someone either uses or proposes to to use white PVC water pipe for underground electrical, when digging the pipe color is the only way to tell what it is & if someone choose to use gray for water, & white for electrical there can be problems.

Many years ago was repairing a sprinkler & there was a bundle of white PVC pipe & 2 of them were in my way, so decided to cut them out of my way then repair them after the first one was repaired, turned out someone pulled a 14/2 UF cable in one of them, thankfully not live.
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Your experience (I would call a near miss) is exactly why we don't want to be pulling wire through plumbing pipe. NOT SAFE. I too if trenching would consider it "ok" to just cut a white pipe to get it out of the way temporarily, but I would also question why was the water run so shallow, here in NE water need to be at least 3-3.5 ft below grade for freezing and electrical is only 18 to 24 inches.
Beyond that My experience with the white plumbing sched 40 is that it is way more brittle than the UL grey pipe. It dosen't accept "crushing" as well as grey. Grey will "crush" without fracturing as readily as plumbing (my experience no mfg supporting data), not that we want the pipe to crush but it is less likely to damage the wire in such event than the white. An important consideration if what it sounds like from OP will have traffic loading running over it.
And I'll hear all sorts of excuses for doing other than the grey, from "they don't have the fittings" to "its cheaper", or "I'm the only one that is ever going to see it". But regardless NEC requirement is for the UL listed Grey 40 or 80 for PVC pipe and as #norcal highlights using the wrong pipe could get someone killed. And if that's not enough reason to do it right I don't know one.
 
fastline said:
We have done many different projects with different backfills, from native soils, to BD2, sands, CLSM, even concrete. The main concern or thought is rework if ever needed. Concrete is just a no! CLSM has to be ordered at very low strength and is much more expensive! I am inclined to use a sand type backfill but I need to ensure it will survive. Any good or bad experiences along these lines that we can apply to this design?
Click to expand...
Well compacted sand with about 8" of crush and run on top to grade should hold up fine unless you have possible migration issues underground. If you do then a stout filter fabric should take care of that.

How deep are you planning to install the conduits? Are you going to follow the 24" cover requirements?
 
fastline said:
Well, we call it flowable fill around here but I realize CLSM is the 'correct' term.

Regardless, at least around here, it is quite expensive! concrete guys get about 20% less than concrete for it! and I will probably need 10yds of it! Has anyone seen any actual pipe failures? I suspect the water pipes will show me issues before electrics will.

Only time I have ever actually seen a failure was our fresh 24" golfcourse water lines and 2" pipe. They were just native fill with a trench compactor every 1ft. Continuous dump truck traffic took a couple of them out, and always right on a fitting or 90*....
Click to expand...
flowable fill is about 110-140 per yard, depending on where you at. You said 10 yards.. $1100-1400
An excavation 18” wide and 24” deep hat is 90’ long is 10 yards...
1 man can fill the trench with this method
How many people and how much time would it take a crew to backfill and tamp the excavation? Will they do it in 6” lifts?
will it be tamped correctly so that you know you won’t be back to repair a settled ditch in the finished driveway a year from now? The labor savings alone is worth it, IMO..
if you have to go back on just one for repair the cost is further justified.
 
Sparky, white pipe is being considers just as a cost measure. I people always say "just spend a little more and...." well a little x100 = A LOT! We are getting out of control with the budget. Not because I need to just run a conduit, it's because they will be all over the place.

Intention is to run these 36" deep. If I backfill with CLSM, it would only be a partial trench fill as the rest just would not really do anything structurally. We do our own dirt work and have for 30yrs.

As far as someone hitting these, I realize some just don't quite understand the situation. My personal place, keeping till i'm dead, no one digs without me, and every single line on this property is not only getting ribbon in the trench, but geo located on a coordinate map with using our total station.

Fred did bring up a good point that I have noticed too! I think pressure rated white pipe is a bit more brittle and gray is more ductile being that it does not need a pressure rating.
 
I never have nor would use PVC plumbing pipe as conduit.

I have, in a pinch, used a galvanized plumbing nipple, but I reamed it very well.
 
fastline said:
Sparky, white pipe is being considers just as a cost measure. I people always say "just spend a little more and...." well a little x100 = A LOT! We are getting out of control with the budget. Not because I need to just run a conduit, it's because they will be all over the place.

Intention is to run these 36" deep. If I backfill with CLSM, it would only be a partial trench fill as the rest just would not really do anything structurally. We do our own dirt work and have for 30yrs.

As far as someone hitting these, I realize some just don't quite understand the situation. My personal place, keeping till i'm dead, no one digs without me, and every single line on this property is not only getting ribbon in the trench, but geo located on a coordinate map with using our total station.

Fred did bring up a good point that I have noticed too! I think pressure rated white pipe is a bit more brittle and gray is more ductile being that it does not need a pressure rating.
Click to expand...

Thank you for that acknowledgement. But I'm sorry, your intentions to run 36 inch depth is even more concerning in relationship to the issue raised by #norcal in post #9, the ease for confusion and assumption that line is water because it is a white pipe (even if you run tracer tape) can be deadly. And as mentioned in other posts tracer is oftentimes hit and missed during excavations.
Yes your intention that no one but you will be digging on site is commendable but seemingly short sited, we all go at some point, and the hidden danger will still be there. It's one thing to make a mistake, we all do, but to knowingly make a potentially deadly installation that's a whole different thing. 480V is deadly no matter how you look at it if you accidentally cut into it.
How much does a WC claim for a death or injury cost? How much is a life worth?
I just priced through HD both types schedule 40- 3" ENT and white PVC, cost difference by 1000 ft? $1203 more for 1000ft of ENT than PVC. Then you have to add in the PVC couplers that would add into the cost of white PVC (no bell ends on PVC) $158. When you do that ENT costs just $1045 more than PVC. And I know you can get it cheaper from the supply house than HD.
I do this type of work for a living and I would hope that if someone had intentionally created this danger and I was hurt or killed as a result that my family was taken care of.
 
Fred B said:
Your experience (I would call a near miss) is exactly why we don't want to be pulling wire through plumbing pipe. NOT SAFE. I too if trenching would consider it "ok" to just cut a white pipe to get it out of the way temporarily, but I would also question why was the water run so shallow, here in NE water need to be at least 3-3.5 ft below grade for freezing and electrical is only 18 to 24 inches.
Beyond that My experience with the white plumbing sched 40 is that it is way more brittle than the UL grey pipe. It dosen't accept "crushing" as well as grey. Grey will "crush" without fracturing as readily as plumbing (my experience no mfg supporting data), not that we want the pipe to crush but it is less likely to damage the wire in such event than the white. An important consideration if what it sounds like from OP will have traffic loading running over it.
And I'll hear all sorts of excuses for doing other than the grey, from "they don't have the fittings" to "its cheaper", or "I'm the only one that is ever going to see it". But regardless NEC requirement is for the UL listed Grey 40 or 80 for PVC pipe and as #norcal highlights using the wrong pipe could get someone killed. And if that's not enough reason to do it right I don't know one.
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There is no code prohibiting sleeving UF in plumbing pipe. It is up to whomever is doing the work to verify what is in a pipe before cutting into it. You cannot blame what someone does today on what someone did in the past.
 
petersonra said:
There is no code prohibiting sleeving UF in plumbing pipe. It is up to whomever is doing the work to verify what is in a pipe before cutting into it. You cannot blame what someone does today on what someone did in the past.
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If sleeving you are doing so for protection from damage. UF cable code part II Installation 340.10(1) references underground requirements per 300.5.
300.5(D)(1-4)where (4) is option to use PVC one would reference 352.2 and 352.6 that states:
"352.6 Listing Requirements. PVC conduit, factory elbows, and associated fittings shall be listed." (Italics mine)
This would preclude use of plumbing type PVC even for sleeving of UF.
 
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