MC Cable in PVC Conduit In Floor Slab

Status
Not open for further replies.

teqniqal

Member
Location
Fort Worth,TX
I have looked-over the NEC Article 330 and other sections for definitions of ‘wet locations’ and from what I see, it is 300.50(B) Wet Locations that says "the interior of . . . raceways installed underground shall shall be considered to be wet locations". Also, Article 100 Definition of ‘Location-Wet’ is clear that ‘in-slab’ is basically the same as ‘underground’ (although to me this is two different things). 352.10(A) and (G) permits PVC conduits to be installed in concrete floor slabs, and (D) in ‘wet locations’, with the caveat that “they shall be installed and equipped so as to prevent water from entering the conduit.” 330.10(7) says MC can be used in ‘Any raceway”, so it seems to me that the PVC conduit creates the ‘dry location’ that is required for the MC cable if it is in the slab (not under it) and it is sealed against moisture (which the joints should be).

So the opinions I am looking for are regarding the installation of MC in PVC conduits run in a slab. We don't want to direct bury the MC in the slab, and we don't want to use liquid-tight MC. Thoughts?
 

luckylerado

Senior Member
.... it seems to me that the PVC conduit creates the ‘dry location’ ......

Still a wet location. Why not transition above ground?

330 does not strictly prohibit MC in wet locations.

330.10 Uses Permitted
(A)
(11) In wet locations where a corrosion-resistant jacket is provided
over the metallic covering and any of the following
conditions are met:
a. The metallic covering is impervious to moisture.
b. A jacket resistant to moisture is provided under the
metal covering.
c. The insulated conductors under the metallic covering
are listed for use in wet locations.
 

Smart $

Esteemed Member
Location
Ohio
If this is a slab above grade, no problem.

If slab on grade with moisture barrier and PVC is embedded in the slab, consult your local AHJ before proceeding.

If slab on grade and no moisture barrier, there's not a chance on God's green earth IMO that an AHJ is going to call it a dry location.

JMO :D
 

roger

Moderator
Staff member
Location
Fl
Occupation
Retired Electrician
What's the reason you have to install MC in the raceways in the first place? Why not use a "W" type conductor and transition to MC above the slab?

There's no getting around the fact that the NEC says your location is a wet location.

Roger
 

hbiss

EC, Westchester, New York NEC: 2014
Location
Hawthorne, New York NEC: 2014
Occupation
EC
What's the reason you have to install MC in the raceways in the first place? Why not use a "W" type conductor and transition to MC above the slab?

I agree. That's the usual way to do it. Why would you even want to push MC through conduit??

-Hal
 

iwire

Moderator
Staff member
Location
Massachusetts
Why would you even want to push MC through conduit??

When it is not a violation its easy and convenient.

Lets say I have a surface mounted panel on one side of the room and the customer wants a surface mounted plug on the other side of the room.

I run MC from point to point through the ceiling and run it down to the panel and outlet in EMT. No box, no splice, no THWN to carry in addition to the MC etc.

We do this same thing with MC feeders as well.
 

Smart $

Esteemed Member
Location
Ohio
...
I run MC from point to point through the ceiling and run it down to the panel and outlet in EMT. No box, no splice, no THWN to carry in addition to the MC etc.
...
And you make proper transitions to EMT in doing so... :D
 

iwire

Moderator
Staff member
Location
Massachusetts
And you make proper transitions to EMT in doing so... :D


UL says its up to the AHJ to determine if the use of a listed product is OK. :D

The use of threaded conduit couplings to make transition is well established here or even the fitting listed for 1/2" EMT to NM but used with MC, AC and 3/8" FMC.
 

iwire

Moderator
Staff member
Location
Massachusetts
Just remembered last week I had to run a 12/2 and a 12/4 down a single 3/4" EMT. I thought of using a 3/4" EMT connector, conduit coupling, 1/2" x3/4" reducing bushing and a double MC connector.

Instead I just used a 4" square box as the 'coupling' and ran straight through the box with no splices or grounding pigtail. I don't think this one has any listing issues.
 

Smart $

Esteemed Member
Location
Ohio
UL says its up to the AHJ to determine if the use of a listed product is OK. :D

The use of threaded conduit couplings to make transition is well established here or even the fitting listed for 1/2" EMT to NM but used with MC, AC and 3/8" FMC.

Just remembered last week I had to run a 12/2 and a 12/4 down a single 3/4" EMT. I thought of using a 3/4" EMT connector, conduit coupling, 1/2" x3/4" reducing bushing and a double MC connector.

Instead I just used a 4" square box as the 'coupling' and ran straight through the box with no splices or grounding pigtail. I don't think this one has any listing issues.
Professionalism at its finest. :thumbsup:
 

hbiss

EC, Westchester, New York NEC: 2014
Location
Hawthorne, New York NEC: 2014
Occupation
EC
I run MC from point to point through the ceiling and run it down to the panel and outlet in EMT. No box, no splice, no THWN to carry in addition to the MC etc.

Sure, I do that all the time also. But what I got from the OP was that he wanted to just push the MC without removing the armor through the conduit. Normally that wouldn't be a problem except if the conduit is considered a wet location.

-Hal
 

ActionDave

Chief Moderator
Staff member
Location
Durango, CO, 10 h 20 min from the winged horses.
Occupation
Licensed Electrician
Just remembered last week I had to run a 12/2 and a 12/4 down a single 3/4" EMT. I thought of using a 3/4" EMT connector, conduit coupling, 1/2" x3/4" reducing bushing and a double MC connector.

Instead I just used a 4" square box as the 'coupling' and ran straight through the box with no splices or grounding pigtail. I don't think this one has any listing issues.

Professionalism at its finest. :thumbsup:
What's wrong with it? I would do the same thing.
 
Status
Not open for further replies.
Top