Running wire for island receptacle in kitchen remodel

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MTcummins

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quote; if you leave a pocket under there, the slab support will be compromised and you could get slab cracking

You are underestimating the strength of concrete. I had to break into the floor of a supermarket once, and the ENTIRE subsoil had settled 18" so the entire floor was being supported by the foundations for the roof columns, and it was NOT cracking even with the public traffic through the store. In many cases, residential floors already have a void under them, which makes it easier to break a hole in the floor. You definitely want a conduit for the wires, if for no other reason than future changes in the island.

If you want to do that to your house, go for it... I wouldn't leave a void under my concrete (and my concrete is only in the basement with no finishes on top of it). It MAY not crack, but you are significantly increasing the chance that it will. Just because voids happen doesn't mean you should do it intentionally. Pretty sure the code officials would have something to say about that, with how particular they are about proper prep after busting out a slab to run lines underneath.

If this were me, I'd get a diamond blade for your circ saw, cut a trench about 2" wide, drop the wire down in there in conduit, and fill the void. It really wouldn't be that bad... you'll spend a little more money on parts, but you'll be done much faster with a better install than trying to fish under the slab. On that short of a trench, I'd not be overly concerned about the strength of the slab being compromised, unless of course it is a tensioned slab... but that wouldn't be too common unless you're in a large building.
 

Terry

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cinnabon_classic_lg.gif

When I was plumbing at the Southcenter Mall, the dirt had settled about eight inches below the slab. We were plumbing in a new Cinnabon resturant. We made a large hole that we could drop down into, and tunneled our way under the slab for all the plumbing runs. We hung the new pipes from the slab with threaded rod and hangers. It was all fine until I was at the end with my head facing away from the hole, about thirty feet from the opening and I would need to slither backwards the entire distance and navigate two right angle turns to get out and someone started yelling "Earthquake!" I slithered back out and said, "I'm done under there." I'm very claustrophobic, and it was all I could do to make myself be down there in the first place. I finished the job doing the top out and let the others guys do the crawl after that.My backpacking sleeping bag is pretty big too. I can't do the mummy bag thing.
 
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Ballvalve

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Cut a groove in the concrete and lay the conduit in it. It will be cemented in so it does NOT need 2" of cover. It is NOT the same as installing a conduit BEFORE the concrete is poured. I hope when you say "A outlet", or "I would like to have ONE anyway", that you do NOT mean you will install a SINGLE outlet on the island.

My sentiment exactly. Save that monster slot for a sewer line. You do not want to cut all your mesh or rebar.

And if you guys are finding so many floating slabs, I would say the world needs to learn how to use compactors or pea gravel on jobsites.
 

Speedy Petey

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My sentiment exactly. Save that monster slot for a sewer line. You do not want to cut all your mesh or rebar.
"Monster slot"?? Seriously?
Since when is a 4" cut in a slab monstrous?

What you are suggesting is NOT code complaint. I have done enough cuts in slabs for this exact type of installation it's not funny. There is nothing monster other than the mess.
 

TJanak

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Speedy,

To make sure, is MC cable code compliant, particularly aluminum sheathed? If I do the hole on each end and tunnel between then conduit becomes much more difficult.

I think I even have some MC.
 

Speedy Petey

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Speedy,

To make sure, is MC cable code compliant, particularly aluminum sheathed?
No!

There is a type of MC that is plastic coated that can be used. I believe the Canadians call it Tek cable, but I for one have never even seen it for sale in any area I have shopped. You CANNOT use "regular" MC cable though.
I really can't see any benefit over conduit though.
 

hj

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quote; unless of course it is a tensioned slab... but that wouldn't be too common unless you're in a large building.

In this area there are many entire housing projects with tensioned slabs and they ALL have a stamping inside the garage and outside in the driveway stating "post stressed concrete slab. DO NOT cut, break, or drill this slab for ANY reason".
 

Jimbo

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Friend of mine has a major remodel underway on his house...2nd story addition, etc. They are doing what is pretty common here in San Diego....the house was essentially demolished. Literally ONE wall left standing. That way, it is still permitted as a REMODEL. If they took down that last wall, it would then be NEW CONTSTRUCTION....all kinds of zoning issues, etc.

ANYWAY, the contractor found that the slab was post-tensioned. Not common in this area, and the markings did not exactly show up as described. They figured it out after all the walls were down, and fortunately before they started cutting. Can you say "CHANGE ORDER" !!!!!!!
 

MTcummins

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quote; unless of course it is a tensioned slab... but that wouldn't be too common unless you're in a large building.

In this area there are many entire housing projects with tensioned slabs and they ALL have a stamping inside the garage and outside in the driveway stating "post stressed concrete slab. DO NOT cut, break, or drill this slab for ANY reason".

Good to know... I didn't think that was common practice in single family housing.

Around here, everyone has a basement... I dunno how people can stand being on a slab, would drive me crazy. A post-tensioned slab... that would be a deal breaker for me buying a house. Pretty much guaranteeing that you can never remodel more than the finishes. No thanks.
 

DonL

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Good to know... I didn't think that was common practice in single family housing.

Around here, everyone has a basement... I dunno how people can stand being on a slab, would drive me crazy. A post-tensioned slab... that would be a deal breaker for me buying a house. Pretty much guaranteeing that you can never remodel more than the finishes. No thanks.

Some areas around here require the tensioned slab, even on a Garage for a home.

If You have to be on a slab it is good insurance, Because Concrete Will crack. At least around here.

And it does not mater how thick it is.
 

MTcummins

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Some areas around here require the tensioned slab, even on a Garage for a home.

If You have to be on a slab it is good insurance, Because Concrete Will crack. At least around here.

And it does not mater how thick it is.

Interesting. Guess it all depends on the soil and its bearing abilities...

I never run into those things, but then again, my house is almost as old as your state... a large portion of our housing stock is well over 100 years old. Construction methods are a little different now than back then. My basement walls are about 18" thick stacked stone, and the framing is true 3" by 4" timbers. They don't make em like that anymore, but of course that comes with some bad building techniques too. Those old techniques keep me in business, fixing all the old houses.

I wouldn't have it any other way... I'll never be a new construction guy - love the history of these old places, even with all the headaches it sometimes brings.

Anyway, I've digressed this thread long/far enough. I still vote you cut it out and lay in conduit. If you have a tensioned slab, then you probably can't safely do either, so the post tension thing is a bit irrelevant to this thread.
 

jadnashua

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Post tensioned slabs tend to be used in earthquake areas and where there is unstable soil with clay as one major one. Clay can expand and contract a lot when its moisture content changes
 

DonL

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Post tensioned slabs tend to be used in earthquake areas and where there is unstable soil with clay as one major one. Clay can expand and contract a lot when its moisture content changes

Mainly Clay in this region, and it sucks.

Everyone's slab have been cracking because of the drought. And the Roads are getting real bad.


Is there any Foundation repair for a slab that Really works ?
 

TJanak

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Keeping the soil wet around the house.

But it takes a decent amount of water, especially if you have bushes, trees, etc. I don't thing running one soaker hose around the slab is enough. I like to keep it wet 8' out or so.
 

MTcummins

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Keeping the soil wet around the house.

But it takes a decent amount of water, especially if you have bushes, trees, etc. I don't thing running one soaker hose around the slab is enough. I like to keep it wet 8' out or so.

Heh, and around here we're trying to keep water away from the house for 8' or so to keep it out of our basements... Gotta love how different things are from one place to another.
 

Ballvalve

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Frank Lloyd Wright built homes in Wisconsin, with its 8' frostline on slabs supported by a few feet of compacted road base. Never a crack yet. no footings. Let it float, don't fight mother nature.

And remember: no sump pump, and a big barn costs less than a basement.
 
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KD

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I would use rigid steel conduit. There is no cover requirement but I usually cover it with an inch or more of concrete patching mortar. I recommend coating the cut concrete edges with concrete bond coating (glue). You could also use ENT encased in concrete your AHJ will tell you how much conc. coverage you need.
 

Ballvalve

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Rigid conduit in a slab sure seems safe to me. More likely to get killed hanging a picture on a wall than from penetrating that pipe. then we have direct burial cable, a good joke.
 

Becky Graf

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You'd need to get at least 2" of cover, so it is best to cut the slab about 4" wide down to the dirt and lay conduit.
Hello - this is an old thread but applies to our remodel and i am not sure if 2017 codes changed since above is from 2011. we rotated the island and to get the 3 way switches to the island we have cut a 7' by 6" trench in the slab. we are through the 4" of concrete and into 3/4" gravel... Our plan is to run the romex through conduit from the wall to the island. Can we use flexible NM (like Liquid-Tuff LFNC-B) or must it be rigid PVC? and is sched 40 sufficent and how deep does this conduit need to be?
Thank you!
 
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