EMT Concrete Floor Recept.?

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360Youth

Senior Member
Location
Newport, NC
We are roughing in a home with slab floor and HO has decided they want floor receptacles. The foreman wants to install with EMT as opposed to pvc but I have never concrete encased installed floor box with emt. I told him seepage may be an issue. Can anyone point me in the right direction, or will it have to be a Carlon/Hubbell-type pvc box?
 

satcom

Senior Member
C3PO said:
I think a pvc floor box with pvc conduit would be a lot easier. Why does the forman want to use emt?
Sure hope this experienced forman understands that cement will destroy the EMT, that is why we use rigid or PVC for cement encased work. We do a lot of repair work where someone used EMT in cement, and it is usually a nasty mess to clean up.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
EMT is often installed in on grade slabs without any problems. The following is from the UL Guide Information for Electrical Metallic Tubing (FJMX)
Galvanized steel electrical metallic tubing installed in concrete on grade or above generally requires no supplementary corrosion protection. Galvanized steel electrical metallic tubing in concrete slab below grade level may require supplementary corrosion protection.
 

satcom

Senior Member
don_resqcapt19 said:
EMT is often installed in on grade slabs without any problems. The following is from the UL Guide Information for Electrical Metallic Tubing (FJMX)
Don,

The worst damage occures where the EMT comes out of the slab, and connects to boxes, we had many buildings where dog housed just corroded at the base and seperated at the EMT water from constant cleaning of the floors. Other issues are where the EMT is in expansion joints on deck floors, the UL tests are done under, other then real world applactions.
The electrical industry seams to be following the auto makers policies run the stamp until the part fails then back off one and market it to death to cure the problems.
 
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satcom

Senior Member
cowboyjwc said:
This is the second question in a couple of days about putting EMT in ground.

Did PVC prices take a big jump or something?:smile:
John, they are allowed to use the EMT, but in my opinion a bad choice under certin conditions, your right PVC took a bump.
 

macmikeman

Senior Member
satcom said:
Sure hope this experienced forman understands that cement will destroy the EMT, that is why we use rigid or PVC for cement encased work. We do a lot of repair work where someone used EMT in cement, and it is usually a nasty mess to clean up.
I do a fair amount of highrise remodel work. Most existing emt in the floors above grade has had no problems unless the water pipes have leaked someplace and contributed to rusting. Grade level floors have problems. It's not so much the cement that degrades the emt, its the moisture levels present. In a slab on grade or below grade, I would only use pvc. Does your foreman plan to pack the max amount of conductors he can get away with from the chapter 9 appendix tables into the emt conduit to that floor box? Could that be why he wants to use emt instead of pvc?
 

360Youth

Senior Member
Location
Newport, NC
macmikeman said:
Does your foreman plan to pack the max amount of conductors he can get away with from the chapter 9 appendix tables into the emt conduit to that floor box? Could that be why he wants to use emt instead of pvc?
I think he wants to take advantage of the "thinwall" characteristic because it is a retro add. The slab (living room of a home) is only 4" thick with rebar throughout. He wants an alternative should there be any problems with fitting pvc and pvc couplings into a trench. We have discussed the NEC depth issues, but his rationale is trench filled in w/ concrete and covered in tile in a residential walking traffic area.

Edit to add: There will be only 3-wire bc in whatever conduit goes into the slab for a switched receptacle.
 
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cowboyjwc

Moderator
Staff member
Location
Simi Valley, CA
satcom said:
John, they are allowed to use the EMT, but in my opinion a bad choice under certin conditions, your right PVC took a bump.
Yes, I agree on both counts. I was only joking about the PVC price hit, but I guess that any petrolium based product shoud be taking a hit right about now.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
360Youth said:
We have discussed the NEC depth issues, but his rationale is trench filled in w/ concrete and covered in tile in a residential walking traffic area.
There are no cover requirements for conduits in or under slabs that are inside buildings. See Table 300.5.
 

360Youth

Senior Member
Location
Newport, NC
don_resqcapt19 said:
There are no cover requirements for conduits in or under slabs that are inside buildings. See Table 300.5.

It is truly annoying how many times you can look at something and not see it. :roll: Thanks. I knew something did not did not seem right, but I could not see the forrest for the trees. You get so busy looking for something, you don't see the one thing you need to. :smile:
 

satcom

Senior Member
macmikeman said:
I do a fair amount of highrise remodel work. Most existing emt in the floors above grade has had no problems unless the water pipes have leaked someplace and contributed to rusting. Grade level floors have problems.
We have done more then a fair amount of work in both hise rise fit_ups and deck slabs, and we found many problems with EMT, It may be due the some conditions found in different parts of the country, all most all high rise work and commercial wes designed with rigid, until prices forced the use of cheaper materials, are they code you bet they are, bare min. requirements, not the best design or craft installed jobs.
 

macmikeman

Senior Member
You know there is also the option of coating the emt with a proper sealant to prevent corrosion if that is the issue and taping up the couplings before concrete is applied helps keep it out of the interior of the conduit. I've worked on lots of new highrises in decades past. Never saw one done in rigid above the grade floor. My career only goes back to the mid seventies and pvc was starting to be used for the grade levels. I'm sure before then rigid for pipe runs in upper floor concrete decks may have been the norm. Horse and buggy's were the norm once also:smile: Emt in poured concrete is fine, nothing wrong with it until you mix water issues in. Pvc is the better choice. Galvanized rigid steel conduit rusts out also. Just takes longer.
 

cowboyjwc

Moderator
Staff member
Location
Simi Valley, CA
360Youth said:
It is truly annoying how many times you can look at something and not see it. :roll: Thanks. I knew something did not did not seem right, but I could not see the forrest for the trees. You get so busy looking for something, you don't see the one thing you need to. :smile:
I actually did the same thing, before I changed my mind about my answer.:smile:
 

cadpoint

Senior Member
Location
Durham, NC
What ever you decide, pull a jet-line or string, or greenlee measured tape, as soon as installed, I'd stake down anything accordingly, then add some more!

Buy a couple of two liter coca-cola if the stings don't move after pour and leave them in over night. It will eat up any concrete in 24 hours...

Pull a bouy or Rat through and suction up anything left if theres a problem...
 

wireman71

Senior Member
Why try and do something that everyone is saying you shouldn't do? Just tell the general that your the EC and you're using PVC. PVC is a heck of a lot faster to lay down also.
 

quogueelectric

Senior Member
Location
new york
satcom said:
Sure hope this experienced forman understands that cement will destroy the EMT, that is why we use rigid or PVC for cement encased work. We do a lot of repair work where someone used EMT in cement, and it is usually a nasty mess to clean up.
Concrete does not destroy emt get a grip
 

satcom

Senior Member
quogueelectric said:
Concrete does not destroy emt get a grip
Have you been reading everything, EMT is approved for use in cement, where the problems come up are when it stubs up and water from constant cleaning eats away the EMT, one of the reasons I don't life the EMT in deck work is before the deck is pored the EMT can get damaged, I notice everyone is jumping on the it's ok to use, of course it is, but that does not make it the best choice under all conditions.
 
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