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What If: Electrical Question

wwhitney said:
The "proper" way to detail a slab on grade within the thermal envelope in cold climates (capillary break, under-slab and perimeter insulation, vapor barrier) is going to yield a dry location for conduit within it when well executed.

The actual way that slabs on grade are usually detailed in warm climates won't.

Cheers, Wayne
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The interesting thing is that I am not from Florida; I am from the cold climate north with frost depths. Your hypothetical "well-executed" thought is just that, a thought lacking reality. I tried to buy a ticket to Perfect World once, but I could not afford one. I then realized that no one can afford a ticket to Perfect World.

What I can tell you is that conduit below grade, even below a slab on grade, with or without a vapor barrier, fills with water. As a matter of fact, electrical embedded in concrete that is on or below grade has been known to fill with water. Each fitting is an opening waiting to be filled with water, including the water in the concrete as it settles.

You can post a reply to this and get in the last word, and create whatever magically perfect scenario you want. I will say, "Sure, it's possible." However, in the real world, NM cable in conduit below grade is a violation and will get written up as a deficiency in citing the correct code sections of the NEC. I am waiting for the day that a contractor appeals that violation and goes in front of the appeals board or building code advisory board and pleas their case to experienced professionals. Until then, the members of this board have lived in the real world, where this is a violation, and electricians know better than to pull NM cables through underground conduits. Hell, it is way harder to pull NM cable through conduit than it is THWN. That would be an act of stupidity.

I am departing this ridiculousness so please, have the last word.
 
jar546 said:
I am departing this ridiculousness so please, have the last word.
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OK, thanks.

In determining whether the conduit is a dry location, what matters is not whether the conduit is embedded in concrete or gravel or wood or whatever. What matters is whether the conduit stays within the controlled envelope. Sometimes the top of the slab on grade is the envelope boundary, sometimes the slab on grade is entirely within the envelope.

Cheers, Wayne
 
I have a slab. It's below grade. It's dry. I'm sure that has nothing to do with proper installation and construction techniques and is simple dumb luck.
 
Are you sure nobody can afford a ticket to perfect world? Maybe there have been a few, but we will never know for sure because they darn sure aren't coming back. If I ever get there, that is the last anyone will ever see of of me, so there will never be proof I actually made it.
 
If there ever was a place that was a perfect World, I would not have been let in. Well maybe for a tour but no camera allowed.
 
jar546 said:
We can see the NM cable entering the 1900 box from above. What if you found NM cable coming up into the box from inside the PVC/ENT below?
They did not call for inspection yet so don't look at anything else unless it is electrical. Lets not get off topic.

View attachment 14791
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Corrections: 1. Two different types of Non-compatible conduit/ raceway.
2. The blue flex conduit is only used for low voltage in CA.
3. Box termination fitting incompatible with conduit attached.
4. If there is NM cable inside the conduit, not allowed in wet location. Slab on grade is considered a wet location.
5. Conduit entering from underground must be sealed at its termination around conductors, and the two that have been cut off.
6. Sleeves or foam wrap required around all penetrations in the slab and annular space shall be sealed.
DIY work?
 
TDCalBI said:
Corrections: 1. Two different types of Non-compatible conduit/ raceway.
2. The blue flex conduit is only used for low voltage in CA.
3. Box termination fitting incompatible with conduit attached.
4. If there is NM cable inside the conduit, not allowed in wet location. Slab on grade is considered a wet location.
5. Conduit entering from underground must be sealed at its termination around conductors, and the two that have been cut off.
6. Sleeves or foam wrap required around all penetrations in the slab and annular space shall be sealed.
Click to expand...

1) ENT conduit may be used with Schedule 40 PVC fittings when used with ENT cement.
2) I see no such amendment to Article 362 of the NEC in California
3) See (1). Possibly the angle between the ENT and the connector is a sign of improper cementing, I'm not sure on that.
4) A slab on grade is often, but not always, a wet location, see the earlier discussion.
5) It is unclear if the conduits are entering from underground. If they are, then NEC 300.5(G) does require the seals you mentioned (and the conduit would be a wet location). But if the conduit is run entirely within the slab on grade, that is not underground, and 300.5(G) does not apply. 300.7(A) could apply if there is no insulation under the slab and it gets cold enough.
6) Certainly best practice, but is that a code requirement? What code and section?

Cheers, Wayne
 
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