NM in conduit under slab

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electrofelon

electrofelon

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Location
Cherry Valley NY, Seattle, WA
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Electrician
So I was looking back at the "old wives tale code" thread I started and I noticed that allenwayne had wrote: NM in conduit under slab (meaning that it as actually not acceptable). Could someone give me a code reference for this? 300.5 (D)? If so it seems one could argue that wouldnt apply. Comments?
 
Re: NM in conduit under slab

Atr 100: Location, wet Art 334.10A "permitted in normally dry locations"
 
Re: NM in conduit under slab

Did you mean 300.5(D)(4)? If so, I believe this would allow URD and UF cable to be sleeved in conduit. Not sure if it directly applies to NM cable since it is not a direct burial cable.
 
Re: NM in conduit under slab

I dont understand why 300.5(D)(5) even exists. 300.5 (D) states that:

"direct buried conductors and cables shall be be protected from physical damage in accordance with (1) through (5)"

Then 300.5 (D) (5) states that:

"cables and insulated conductors installed in enclosures or raceways in underground installations shall be listed for use in wet locations"

Now if something is approved for direct burial, which is what 300.5 (D) is about, then wont it also be approved for wet locations anyway??
 
Re: NM in conduit under slab

I got tagged for pulling THHN/THWN conductors through 2" pvc underground for a garage feed. The AHJ required I pull it out and use direct burial conductors. That was the only time I have ever been tagged for this. Is there a code reference for this?

[ February 15, 2006, 08:47 PM: Message edited by: Matt Harp ]
 
Re: NM in conduit under slab

Originally posted by Matt Harp:
I got tagged for pulling THHN/THWN conductors through 2" pvc underground for a garage feed.
Click to expand...
I think that was a bad call on the part of the AHJ. Look at Table 310.13 and you'll see THWN as listed for wet locations.

Also, almost all THHN is actually THHN-2 which, as Note 4 under Table 310.13 states, makes the THHN suitable for wet locations.
 
Re: NM in conduit under slab

Originally posted by Matt Harp:
I got tagged for pulling THHN/THWN conductors through 2" pvc underground for a garage feed. The AHJ required I pull it out and use direct burial conductors. That was the only time I have ever been tagged for this. Is there a code reference for this?
Click to expand...
Yep AL, bad call.


Is he still requiring DB in conduit? :p
 
Re: NM in conduit under slab

Originally posted by electrofelon:
Now if something is approved for direct burial, which is what 300.5 (D) is about, then wont it also be approved for wet locations anyway??
Click to expand...
Being approved for a wet location is not the same thing as being approved for direct burial.

THWN, THW, XHHW etc. are not approved for direct burial.

Those conductors are only approved for wet locations. They must be installed in a raceway.
 
Re: NM in conduit under slab

"Also, almost all THHN is actually THHN-2 which, as Note 4 under Table 310.13 states, makes the THHN suitable for wet locations."

Al
The -2 does not take a conductor Type such as THHN and make it suitable for wet locations.

What it does is take a conductor Type such as THWN which is rated for 75 degree C in wet locations and permits the rating to be 90 degree C in wet locations.
 
Re: NM in conduit under slab

1) -300.5(B) Listing. Cables and insulated conductors installed in enclosures or raceways in underground installations shall be listed for use in wet wet locations.
2)-(A) Type NM. Type NM cable shall be permitted as follows:
(1) 334.10(A)For both exposed and concealed work in normally dry locations except as prohibited in 334.10(3)
I think that this covers it.
1)Cable has to be listed for use in wet locations.
2)NM is not permitted in wet locations.
Paul
 
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