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Trench in concrete for electrical

18K views 7 replies 5 participants last post by  Klawman 
#1 ·
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.
 
#3 ·
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.
 
#4 ·
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...........
 
#6 ·
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.
 
#8 ·
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.

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.

My house is about 25 years old and I don't believe they started stamping slabs post tension until a few years later. The house I owned previously was post tension. My neighbor two houses away watched his home being built and says it wasn't post tension. I agreed that it was smart to scan it before cutting as long as we weren't positive that it wasn't PT. Another reason I doubt it is PT is the bars/cables are 2 feet apart and the operator and the job foreman all said that PT is usually much further apart.
My thoughts in bold.
 
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