MC Cable in PVC Conduit In Floor Slab

Status
Not open for further replies.
The mc cable the NEC is reffering to in the earlier post for use in wet locations is a normally green epoxy coated mc cable that can be installed in wet locations and in concrete and cinder fill. we just did a 4 story putting all the branch in the slab using it.
 
roger said:
What's the reason you have to install MC in the raceways in the first place?

Roger
Click to expand...

The steel jacketed MC cable has extremely low Electro-Magnetic (EM) field emissions due to the steel wrapper and the tightly spiraled inner conductors. They would be running underground with low voltage signal cables (audio, video, data) in adjacent conduits. All conduits are PVC so they offer no EM shielding. If we run bare conductors (THHN, etc.) they lie loosely in the PVC and create a larger EM field that can interfere with the nearby low voltage signal cables. It is difficult to get the contractor to order the factory spiraled (twisted) cable groups, although I know it is possible to order these. Steel conduits in slabs don't work (rusting-out), and aluminum conduits only offer Electro-Static Shielding, and PVC conduits offer no shielding.

For those wanting to know more about this, download the "Power Distribution and Grounding of Audio, Video and Telecommunications Equipment White Paper" at http://www.middleatlantic.com/resources/white-papers.aspx

Sadly, I understand that the PVC in-slab conduits are a 'wet location', so maybe we can get the wet location MC to do this.

Thanks to everyone for their responses. I just needed a reality check.
 
teqniqal said:
The steel jacketed MC cable has extremely low Electro-Magnetic (EM) field emissions due to the steel wrapper and the tightly spiraled inner conductors. They would be running underground with low voltage signal cables (audio, video, data) in adjacent conduits. All conduits are PVC so they offer no EM shielding. If we run bare conductors (THHN, etc.) they lie loosely in the PVC and create a larger EM field that can interfere with the nearby low voltage signal cables. It is difficult to get the contractor to order the factory spiraled (twisted) cable groups, although I know it is possible to order these.
Click to expand...
I looked into ordering spiral twisted conductors for a project I was involved in several years ago and did not find any available from any of the major manufactures, at least for 12AWG. I was able to get a good twist using rolls of individual conductors by using stranded wire and alternating the reels to feed from over the top and off the bottom.
Steel conduits in slabs don't work (rusting-out), and aluminum conduits only offer Electro-Static Shielding, and PVC conduits offer no shielding.
Click to expand...
Since energy dissipates at the square of the distance how big of a deal can this be. If you are really concerned about it can it not be managed by simply spacing the power conduits away from low voltage conduits.
 
iwire said:
I have never seen steel conduit in a slab rust out, I think you are overthinking this.

By the way, if you go to Home Depot they sell black, white and green 12 AWG pre twisted into a group.
Click to expand...
I agree. I know of many buildings from as far back as the 50's with steel conduit in slab and under that is still intact.

But, with all that said, you won't have to worry about any of that if you simply use one of these :thumbsup: :D

Roger
 
teqniqal said:
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).

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?
Click to expand...


I disagree with your assertion that in slab is the same as underground. Article 100 definition states "indirect contact with the earth" I haven't seen a building slab poured in at least 10 years that doesn't have a moisture barrier installed. That means the slab is not covered by the definition you referred to. Also, it is very common in this area to run a chase in the slab to a kitchen island and put Romex in it, so I don't think there is going to be an AHJ problem here. None the less, I agree with others when they ask, "why?"
 
Strathead said:
I disagree with your assertion that in slab is the same as underground. Article 100 definition states "indirect contact with the earth" I haven't seen a building slab poured in at least 10 years that doesn't have a moisture barrier installed. That means the slab is not covered by the definition you referred to. Also, it is very common in this area to run a chase in the slab to a kitchen island and put Romex in it, so I don't think there is going to be an AHJ problem here. None the less, I agree with others when they ask, "why?"
Click to expand...
Being your from Florida, I can understand your position. However, in northern states there is more of a possibility that a slab-on-grade's upper surface is actually at or below grade level of the property (think basements and other sub-grade levels). Regardless of a vapor barrier being installed, an AHJ is well within their responsibilities to say conduits embedded in such slabs are in fact underground.
 
Smart $ said:
Being your from Florida, I can understand your position. However, in northern states there is more of a possibility that a slab-on-grade's upper surface is actually at or below grade level of the property (think basements and other sub-grade levels). Regardless of a vapor barrier being installed, an AHJ is well within their responsibilities to say conduits embedded in such slabs are in fact underground.
Click to expand...

I wasn't taking the position that a slab on grade isn't a wet location, I was pointing that it isn't arbitrarily a wet location.

However, I would like to know how you would consider a basement to be a wet location if the entire thing was encased in a properly installed moisture barrier. I have zero construction experience with basements being California and Florida trained, so I don't know the building codes for them, but if the moisture barrier blocks all outside moisture then where would the AHJ be within his rights to declare the area a wet location? Now if only the slab in barriered and the walls aren't or the code doesn't require an actual watertight seal, then I can see it. Again, don't know the codes.
 
Smart $ said:
Being your from Florida, I can understand your position. However, in northern states there is more of a possibility that a slab-on-grade's upper surface is actually at or below grade level of the property (think basements and other sub-grade levels). Regardless of a vapor barrier being installed, an AHJ is well within their responsibilities to say conduits embedded in such slabs are in fact underground.
Click to expand...

How do you code compliantly install NM in a cement trench?
 
iwire said:
Did not mean too, I meant to quote strat
Click to expand...

I didn't say anything about installing NM in a trench, and I didn't mean to imply it. I was referring to running NM in a PVC chase in the slab to an island. Let me be clear that I don't do romex, I am allergic to it. But I see this installation all the time. I am pretty sure that slab on grade, above a moisture barrier is not considered a wet location in Florida. That doesn't address a basement, just slab on grade.
 
Strathead said:
I wasn't taking the position that a slab on grade isn't a wet location, I was pointing that it isn't arbitrarily a wet location.

However, I would like to know how you would consider a basement to be a wet location if the entire thing was encased in a properly installed moisture barrier. I have zero construction experience with basements being California and Florida trained, so I don't know the building codes for them, but if the moisture barrier blocks all outside moisture then where would the AHJ be within his rights to declare the area a wet location? Now if only the slab in barriered and the walls aren't or the code doesn't require an actual watertight seal, then I can see it. Again, don't know the codes.
Click to expand...
A vapor barrier just prevents moisture from coming up through the slab... but it will not help if there is a flood (AHJ will use say 50-year flood plane to establish potential), or heavy rains cause excess ground water to weep into the basement. Sumps will help, but it is an AHJ call whether to consider conduits underground and a wet location.
 
Strathead said:
I didn't say anything about installing NM in a trench, and I didn't mean to imply it. I was referring to running NM in a PVC chase in the slab to an island. Let me be clear that I don't do romex, I am allergic to it. But I see this installation all the time. I am pretty sure that slab on grade, above a moisture barrier is not considered a wet location in Florida. That doesn't address a basement, just slab on grade.
Click to expand...

I just think it's tradition and not really compliant.
 
Can someone explain or locate the conduit within a conduit NEC code. I feel like this conversation has more to do with that code than it does wet location. Is romex sheeth a conduit and thus cannot be put in a pvc conduit. Thus MC is surely classified as a conduit? And should not be pushed through conduit. I have done both in conduit but AHJ doesn't like it because "conduit within conduit". I can't locate a thread already on this.
 
Just where is this prohibition of a conduit within a conduit?
You can have a sheath inside or outside a conduit.
and AFAIK MC is a cable, not a raceway wiring method.
There is a problem running MC or AC inside a conduit, but it has to do with the difficulty of then terminating it in a code compliant way.
 
Strombea said:
Can someone explain or locate the conduit within a conduit NEC code. I feel like this conversation has more to do with that code than it does wet location. Is romex sheeth a conduit and thus cannot be put in a pvc conduit. Thus MC is surely classified as a conduit? And should not be pushed through conduit. I have done both in conduit but AHJ doesn't like it because "conduit within conduit". I can't locate a thread already on this.
Click to expand...

There is no direct prohibition against a conduit within a conduit.

MC is not a conduit it is a cable per its UL listing.

In addition the MC article specifically tells us we can run MC inside a conduit. It does not say if it must be stripped or not.
 
To complicate this further - a sleeve is not a raceway it doesn't even need to be listed electrical PVC - could even make it out of sewer pipe.

Does that still make it a wet location if in a slab on grade?

Are in floor wireways a wet location in this situation, or are they not allowed in slab on grade? I never dealt with those so don't know much about them.

Potential for flooding doesn't seem like it should matter, if it did then possible flood level on walls is wet location as well.
 
kwired said:
...
Are in floor wireways a wet location in this situation, or are they not allowed in slab on grade? I never dealt with those so don't know much about them.
...
Click to expand...
"In-floor wireways" would be covered under Article 390 as Underfloor Raceways.

Code doesn't distinguish or define what is underground and not. That is left up to the AHJ, and that is what would determine if it is considered a wet location.

Article 682: Natural and Artificially Made Bodies of Water is enforceable at any location subject to flooding per the definition of Electrical Datum Plane. Under criteria (3) of that definition, the AHJ can choose the reference.
 
Status
Not open for further replies.
Top