Question came up at the North Florida Division Meeting. I'd like to have some comments on.

In a one family house when you have to slab a Sch 40 PVC conduit to the kitchen island, and they forgot to install it before the slab is poured, you need to saw-cut the slab.

1. What is the depth of the cut that needs to be made?
2. How much cover is required over the SCH. 40 PVC?

Some have thought that a 2" cover with concrete is only required, but others thought that 300-5 would require that the slab needed to be cut completely so the PVC is installed under the building slab.

I have been unable to locate the 2" concrete cover requirement that was indicated. What code sections need to be applied to this installation?
Any thoughts?

Mike, The 2" deal is from 230-6 or 230.6 (and I know what you are going to say next...).

Nick
You got it. But again if someone wants to cut a notch in the slab not cutting through it and cover the notch with 2" of concrete, what code section would I use to approvd that?

Some have said that since I do not conform to the depth as listed in 300-5 than I would need sch 80 instead of sch 40.

Of course if you install a floor box and run that conduit, it is on the ground at the bottom of the slab, so it conforms to 300-5 (Under the Building).

Agreed. Technically, 300-5 is correct. If it was a test question and you answer 2", you would get the question wrong. The slab would have to be fully cut, the conduit installed beneath the building, and covered with the full 4".

230 would not apply since it only covers service conductors.

BUT, cutting through the entire 4" of slab raises another concern. It would compromise the vapor barrier. Personally I would rather see the slab not fully cut, and the PVC covered with at least 2" of concrete. If push came to shove - I could argue that "since the 2" cover is safe enough for service conductors, then it would certainly be safe enough for the kitchen island outlet."

Well, I'm afraid I think I made a mistake, and I'm in desperate need of correcting myself:

The code is correct and table 300.5 is correct after all. If you go down to note 2, it will tell us that where raceways are concrete encased, the envelope will only have to be 2" thick. So note 2 would apply since the raceway is not UNDER the 4" slab, but encased by concrete. This note makes an exception. Thus, it would be in sync with article 230 as well.

If we go to the heading of Column 3, we have to pay attention to the words "without concrete encasement."

Well Nick
Note 2 in 300-5 only applies to raceways that are not approved for direct burial unless they are concrete encased, ie. NMT Article 362. (Smurf). This note permits raceways like Smurf to be installed underground even though they are not approved for direct burial as long as they are concrete encased. Note 2 does not apply to PVC, as pvc is approved for direct burial with or without concrete encasement. See heading in 300.5 column 3.

Article 230.6 is not for protection of the raceway or the conductors from physical damage, but is actually to protect the building. In the event that there was a short circuit in the service conductors and since they do not have overcurrent protection ahead of them, by encasing them in 2" of concrete that will protect the building combustible materials from fire. See the 2002 NEC handbook commentary to 230.70(a) first paragraph, and 230.6 commentary and picture.

But I think that you were correct the first time. Column 3 is for raceways that are approved for direct burial without concrete encasement. But the depth shown in the column for under the building would require that the PVC to be installed on top of the dirt and under the concrete, after all when you install a floor box where are the conduit holes at the bottom or in the middle?

Also there is a special code section Article 390 for underfloor raceways. Specific type raceways.

Since there is no other code section that I am aware of to deal specific with the 2" depth, It would be my opinion that to permit that depth in a slab we would need for require Sch. 80 pvc for protection from physical damage.

Now what do you think?

I think I need a vacation.

But seriously, if the 2" concrete encasement is OK for raceways that are for burial only, then why wouldn't it be OK for raceways listed for direct burial as well? It would be even better.

Why don't we submit a proposal on this?

You know I have accepted the 2" depth in the slab many times, all I'm trying to say is there is no code section that really supports that installation. I'm playing the part of the bad guy on this one just to make a point!

In addition the size of conduit used will determine how deep the slab needs to be cut. Don't forget the 2" depth is to the top of the conduit! So if you had to install a 1" or
1 1/4" PVC for a cooktop, or range, on the island you would have to cut through the slab just to get the 2" depth and concrete cover anyway.

Here is another item to think about:
But with Note 2 to 300.5 if you use a raceway that isn't listed for direct burial and you encase it in 2" of concrete you still have to use the depths as listed in 300.5. If you have PVC conduit and install it in a trench below 2" thick concrete per the table it still needs to have a 12" burial depth! (See Column 3 second table down from the top).

Ok now my brain hurts!

I don't think the code addresses cutting the slab and installing the conduit with a 2" concrete cover. So I think that table 300.5 is all that we have. As I said you could require Sch 80 since that is a raceway that would be suitable for protection against physical damage. If they wanted to cut the slab say 1" and put a scratch coat of concrete and maybe floor tile over it that would be ok with Sch 80, or RMC, or IMC etc...

I think, as I said, that I have accepted the 2" concrete cover in the past because I think it is one of those common sense issues, but at an IAEI meeting I just thought it was necessary to point out how some code sections that are sometimes applied to this problem, do not actually address this issue...and I haven’t been able to find one that did! That’s why I was asking in the first place...hoping that someone could come up with one that I didn't know about.

(The saga continues):

I don't know Mike - You are encouraging me to think further about this and now I'm more convinced that code would allow the 2" cover under note 2. The key is the difference between "listed" and "approved."

If something is listed for direct burial it could easily be approved for burial (see definition of approved) and note 2 could apply. This is, in reality, what is happening when we pass the inspection with only the 2" of cover.

I know, I should stop now and plan that vacation. I'll shut up now. But I think based on the code language that code does cover it, whether it's intentional or not. :p