Underground conduits

Location
Kenosha
Thanks all for any input, but here is a synopsis of the catastrophe we had in our HQ this past week.

We were installing some new equipment and had brought in a concrete cutting company to take off the top slab from the basement floor. During the process it was realized that the concrete was 14" thick, so they came back the next night to start ( I was not informed about this ). Needless to say on there first pass of 6" or so they completely cut through 9 seperate conduits feeding our entire east wing. Now if I was kept in the loop this wouldn't have happened because I never would have approved a cut that depth withought x-ray, but regardless it still has to be fixed. Now for the question

I've always followed the rule of if it's PVC it needs to be run at 18" deep. Now after checking with Table 300.5 I've found that under a building the minimum depth is 0"? Is there no code that protects this from happening, or have I been costing myself money for all these years? i mean some of these conduits were within 3-4" of the top of the cement.

Also I know they make underground feeder splices, but the ones I've seen are for very small conductors. Has anybody else ran into a situation like this and spliced the feeders in the conduit and repaired the conduit with the 2 piece PVC repair kits?

Thanks for any input
 

iwire

Moderator
Staff member
Location
Massachusetts
No NEC minimum cover required in that application.

As builts or x-raying is the only way to avoid hitting conduits.

I have repaired many, it is a pain.

I also core drilled through a conduit myself once, I got lucky it was empty.
 

Ragin Cajun

Senior Member
Location
Upstate S.C.
WOW! Do we assume there were many "sparks"? And no injuries?

I have seen where they cut way below the slab and cut conduits below the slab. That was bad enough. We dug around the remaining conduit and went from there. It will be interesting to see how others solved the problem with conduits IN the slab.

RC
 

iwire

Moderator
Staff member
Location
Massachusetts
It will be interesting to see how others solved the problem with conduits IN the slab.
If you are lucky you force the guy doing the cutting to clear out the concrete around the conduits.

Other times you spend hours with the demo hammer trying to surgically remove the concrete without damaging the PVC.

Normal cement is not so bad, fiber reinforced concrete is a major pain and one of our customers uses it for all thier slabs


http://en.wikipedia.org/wiki/Fiber-reinforced_concrete
 
Location
Kenosha
So I've seen the 3M cold shrink that you can splice a cut feeder and is rated for direct burial after. My question is, I proposed we splice the feeders where cut with a permanent crimped coupling and then use the 3M cold shrink on top of the splice. This would give us a db rating and all the other listings of the cable. Then I would use a 2 piece PVC repair kit around the splices and to connect the two ends of the existing conduit. With the db rating of the newly spliced feeders, would it still be a UL listed application if I installed it in a conduit.

This would change a $250K mistake in to a $25K mistake. It's worth a shot.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
I don't see how it is a $250,000 mistake. It can be repaired for a lot less than that. probably one or two man weeks worth of work.

I can't imagine a concrete cutting company would make cuts like this without some assurances from someone that they were not cutting into something.

Surprised they did not see sparks when they cut through the first conduit. One would have thought the blade would have shorted at least two phases together and if nothing else tripped the CB on that feeder.
 
Location
Kenosha
I've got well over 100K in 600's alone not even counting all the other conductors. The runs are all of 700' all underground. If we replaced all the feeders and repulled, I figure 250k might even be light.

We're not installing any type of floor box to splice the conductors, that;s the reason I was hoping the the in line splices would be ok.

Thanks
 

GoldDigger

Moderator
Staff member
So you are really asking whether it would be OK to make the completed splices inaccessible to the point of covering them with concrete?
If you had direct burial wire at least it would be possible to dig it up again.
Once you have spliced the cables, it is likely that you would have severe problems pulling the wires out again if that were necessary.

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petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
I've got well over 100K in 600's alone not even counting all the other conductors. The runs are all of 700' all underground. If we replaced all the feeders and repulled, I figure 250k might even be light.

We're not installing any type of floor box to splice the conductors, that;s the reason I was hoping the the in line splices would be ok.

Thanks
I see no reason to re-pull them. That serves no real purpose.

I don't think you can just put splices inside the conduits.
 

iwire

Moderator
Staff member
Location
Massachusetts
So I've seen the 3M cold shrink that you can splice a cut feeder and is rated for direct burial after. My question is, I proposed we splice the feeders where cut with a permanent crimped coupling and then use the 3M cold shrink on top of the splice. This would give us a db rating and all the other listings of the cable. Then I would use a 2 piece PVC repair kit around the splices and to connect the two ends of the existing conduit. With the db rating of the newly spliced feeders, would it still be a UL listed application if I installed it in a conduit.

This would change a $250K mistake in to a $25K mistake. It's worth a shot.
There is no code compliant way to conceal the splice like you describe.

Code wise you could add a hand hole / man hole at the break and splice in that.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
presumably they are doing some work in the area anyway since they had to dig up the floor. it does not seem like it would be all that hard to make some kind of provision for legally splicing the conductors back together.
 

GoldDigger

Moderator
Staff member
Unless there will be machinery located on top of them.
Yet another possibility would be to dig two sets of splice boxes in what will be clear areas of the floor along the present wire route and splice new wire to the existing wire there.

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iwire

Moderator
Staff member
Location
Massachusetts
Unless there will be machinery located on top of them.
Yet another possibility would be to dig two sets of splice boxes in what will be clear areas of the floor along the present wire route and splice new wire to the existing wire there.

Please cite the code section prohibiting a splice under machinery. :p
 

GoldDigger

Moderator
Staff member
Please cite the code section prohibiting a splice under machinery. :p
Nothing prohibiting it, but the handhole, if one is required, will certainly be inaccessible. From the OP, it sounds like the equipment is substantial enough that they had to reduce the thickness of the floor to fit it in. And maybe will be pouring new concrete on top?
 

iwire

Moderator
Staff member
Location
Massachusetts
The code requires that the j-box be accessible.

Accessible (as applied to wiring methods). Capable of being removed or exposed without damaging the building structure or finish or not permanently closed in by the structure or finish of the building.
A machine regardless of size is not the structure or finish of the building.

The OP was willing to cement in splices so I don't see machinery as a deal breaker. :)
 
We had this happen once but it involved a fork lift and about 12 4" EMT feeders. I am in favor of a splice box...that way if there is a future cable failure there is access to the splices. It would be a real bummer to have to chip out all that concrete again to fix a failure.


PJHolguin :cool:



I agree, as long as they do not pour new concrete to support the machine and cover the j-box. :)

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