# Trench in concrete for electrical



## Klawman (Nov 10, 2009)

I am wondering about a trench cut into my concrete slab that this contractor is running electrical through to feed a kitchen island. The trench is about 5' long, 3 inches wide, and 2 inches deep. Since the romex is going through 1" plastic pipe, there will only be 1" over the top of the pipe.

The concrete cutter couldn't cut deeper because his scanner indicated that there was post tension cable 3 inches under the surface. [I think it was rebar, as it was only 2 feet apart, but I really don't know.]

I am wondering if this is being buried to shallow and if I should tell the contractor to do it the hard way. Cut cores through the slab, bore horizontal beneath it, and cut another core where the pipe comes up. At least I believe that is the way it is done.


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## ddawg16 (Aug 15, 2011)

Unless someone is going to be parking a car on it, you will be fine.


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## Klawman (Nov 10, 2009)

Thanks ddawg. There were a few minor issues that were cleared up this morning and it looks like our kitchen is coming together. And now I won't hav to give the foreman more grief.

He wasn't here when the concrete cutter showed. He tried to get me to sigh a release of liability and when I wouldn't he packed his stuff up, but then the GC assumed it. We could never get that guy back to cut deeper. He took it real personal that I wouldn't hold him harmless even if he cut a cable.


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## jomama45 (Nov 13, 2008)

Klawman said:


> Thanks ddawg. There were a few minor issues that were cleared up this morning and it looks like our kitchen is coming together. And now I won't hav to give the foreman more grief.
> 
> He wasn't here when the concrete cutter showed. He tried to get me to sigh a release of liability and when I wouldn't he packed his stuff up, but then the GC assumed it. *We could never get that guy back to cut deeper. He took it real personal that I wouldn't hold him harmless even if he cut a cable.*


I can't blame him, theres' plenty of other job's he can go to where he wouldn't have the head aches he could potentially have at your house. Why would he risk the chance of getting sued, or worse yet injured, if he cut through a post tension cable when he clearly knows better? Honestly, when you've been in the trades long enough, and have half of a brain, you know when ot walk away from certain jobs, it's just not worth it for someone to have a few outlets on a kitchen island...........


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## Klawman (Nov 10, 2009)

jomama45 said:


> I can't blame him, theres' plenty of other job's he can go to where he wouldn't have the head aches he could potentially have at your house. Why would he risk the chance of getting sued, or worse yet injured, if he cut through a post tension cable when he clearly knows better? Honestly, when you've been in the trades long enough, and have half of a brain, you know when ot walk away from certain jobs, it's just not worth it for someone to have a few outlets on a kitchen island...........


I am not arguing that the trench should be cut deeper if it is indeed to risky. What I am saying is that the general should then do the job the other way, which is to core a hole under where the island is to be placed and another where the nm goes under ground. That is what the general contracted for if a trench couldn't be cut deep enough.

As for those few outlets, the general was supposed to design a small movable island like table that wouldn't require electrical. After she designed the island table, she insisted it was too heavy not to be fixed to the floor. Any island requires electrical if it is fixed to the floor.


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## intelpcguy (May 10, 2015)

I have never heard of a concrete cutter company carrying scanners, one reason is they want someone else to do the scanning or Xrays, and then based on that Xray / scanning, they are off the hook should the reading be wrong. Though a good concrete cutter can tell the difference between rebar and cable if he's cutting it.

I was on a hotel project, where all the floors were post cable tensioned, and a separate Xray company wall called out for Xrays for before any coring / cutting in slab. Twice the Xray company got it wrong, and twice the concrete guy hit the cable but stopped when all of us ( I was working 2 floors below ) heard and felt the boom, when 3 strands snapped ( the cable had I think 40 strands, the engineer later determined it could lose a few more before compromising the integrity of the cable ). But it scared some guys right below where he was cutting. 

Depending on the age of the house, most houses with post cable in the slab have notices posted in the garage in big orange stickers warning not to cut the slab. Sometimes you can walk the perimeter of a house and see small round rust spots about 2 foot on center, that's usually where they cut the cable after tensioning and packed the end with grout, over time a light rust spot forms over the packed grouted area.


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## concrete_joe (Oct 6, 2014)

cutting a PT cable is bad, it can literally cause the slab to crack the whole length of the cable, and then slab could sag/lift on one side.


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## Klawman (Nov 10, 2009)

intelpcguy said:


> I have never heard of a concrete cutter company carrying scanners, one reason is they want someone else to do the scanning or Xrays, and then based on that Xray / scanning, they are off the hook should the reading be wrong. Though a good concrete cutter can tell the difference between rebar and cable if he's cutting it.
> 
> *The same guy that operated the scanner cut the trench. I think he was seeing rebar.*
> 
> ...


My thoughts in bold.


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