NM in Liquidtite

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dnbob

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Rochester, MN
We are wiring a type V commercial building. Does anyone think it is a problem to sleeve the a/c 240 v. ckt (NM Cable) through 2' of L.T. before the a/c disconnect? 334.15B seems to say it is o.k.?

Thanks,
Bob
 
Re: NM in Liquidtite

No, not ok. You have to use Type THHN/THWN conductors. NM cable contains only type THHN conductor, which are not for use in wet locations.
 
Re: NM in Liquidtite

No, not ok. You have to use Type THHN/THWN conductors. NM cable contains only type THHN conductor, which are not for use in wet locations
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I can't seem to remember, is the area inside of liquidtite conduit installed above ground considered a wet location?
 
Re: NM in Liquidtite

By the article 100 defintion of "Location, Wet" I'd say it is. A raceway installed outdoors cannot be kept dry under any circumstances. Aboveground, the issue is condensation. Undergound, the issue is seepage.
 
Re: NM in Liquidtite

real quiet now. we do this all the time routinely and have not so far been called.we also use it in pvc which is required under a mobile home and so far no call.maybe the inspectors think if its a real short run like 4 or 5 ft it cant be VERY wet.anyhow we use it for whips all the time and have not been called,..................yet.

[ October 20, 2005, 10:11 PM: Message edited by: stew ]
 
Re: NM in Liquidtite

i don't consider above ground pvc or lt wet. it may be damp. if nm is not allowed in those two circumstances, exterior boxes fed with interior nm should also not be up to code. i didn't pour cup fulls of water out from pvc i repaired, nor from liquidtight. the interior of those aluminum boxes was always wet, but only damp by definition.

if pvc and liquidtight are soooo wet, the old rt emt was porous, and i have seen too many dry installations on windward walls. the problems with water came from not sealing around penetrations. there is 30 yr old rt to panel into house wall on my kitchen wall. it rains a real 130" a year normally here, 60"++ in drought years.

if these were really WET locations, then my house should have floated or rotted away by now.

maybe someone is too miserly with the cement and prep time.

for that matter, nm shouldn't be allowed in exterior panels from a house because it is much more likely to flow down into the houses than up from the lt or pvc. ext panels are just as prone to the same problems and even have small holes to the weather.

glad you weren't my inspector, and unless told to do it, not wet by my book.

paul
 
Re: NM in Liquidtite

By the article 100 defintion of "Location, Wet" I'd say it is. A raceway installed outdoors cannot be kept dry under any circumstances. Aboveground, the issue is condensation. Undergound, the issue is seepage.
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I hear what you're saying about condensation but after reading the definition a few times I would say that a piece of LFC used above ground could be argued either way. It does not explicitly define the inside of the raceway above ground as a wet location.
 
Re: NM in Liquidtite

As far as the NEC is concerned, the raceway does not alter the fact that the installation, and the conductors, are outdoors. A damp location is one that is exposed to air-borne moisture, and a wet location is one that is exposed to water, whether above or below ground.
 
Re: NM in Liquidtite

We'll just have to agree to disagree. I would not use NM cable in a raceway for this application. Some of it is personal preference, but I think the NEC supports my position.

With a whip from a disconnect to an AC unit, how hard is it to use 3 pieces of THWN? :confused: I think using NM is the sign of a lazy job, IMO.
 
Re: NM in Liquidtite

The inside of pvc above ground may, very may, be exposed to moisture, same with LT. saying that the raceway is exposed to the weather is the same as the wiring being exposed to the weather doesn't wash. Buildings are exposed to the weather, that doesn't make their interiors either wet or damp locations.
 
Re: NM in Liquidtite

Originally posted by apauling:
Buildings are exposed to the weather, that doesn't make their interiors either wet or damp locations.
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A raceway located on the exterior surface of a building must be arraigned to drain.

How or why do you drain a dry location? :) Here I find most any outdoor raceway with a low spot to be full of water.

Cold at night, warm in the day, humidity and time fill them up.
 
Re: NM in Liquidtite

Location, Wet. Installations under ground or in concrete slabs or masonry in direct contact with the earth; in locations subject to saturation with water or other liquids, such as vehicle washing areas; and in unprotected locations exposed to weather.

334.12
(B) Types NM and NMS. Types NM and NMS cables shall not be used under the following conditions or in the following locations:
(4) Where exposed or subject to excessive moisture or dampness
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This is pretty simple if it is just looked at.
In 100 definitions it states that a place that is not protected from the weather is a wet location.
334.12 (B)(4) states where not exposed to excessive moisture.

If it is on the outside it is in a wet location and this is not allowed by 334.12 (B)(4) with or with out being in a raceway. The raceway will not protect the cable from a humidity of 100% when it is raining.
The question has been asked about under a house in the crawl space. This is why we install ventilators in the foundation. These vents allow air to flow in order to keep the humidity down.

This is also what 550.15(H) is referring to as it pertains to the underside (Exposed to Weather) of a trailer.
:)
 
Re: NM in Liquidtite

Have never been called out for nm as a whip for outdoor unit.Have been called for nm in conduit in a slab and it was a valid call since in or under a slab is considered a wet location and all conductors must be rated for a wet location
Quote
"I think using NM is the sign of a lazy job, IMO. "
That`s a pretty damaging statement,to imply lazy is to imply that the install is a 1/2 a#$#d job ;) especially when you had thhn from nm and it met ampacity :confused:
 
Re: NM in Liquidtite

I am not a huge fan of runnning Nm in any raceway but to call any use of NM "lazy" seems a little excessive. NM is a perfectly sound and safe premises wiring system when used within its limitations.
 
Re: NM in Liquidtite

truck with thwn is far enough away that to stop what you are doing to get thwn would be silly to do
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dang! I wish you guys could get that "didn't have it in the truck" exception added to all articles...it would make it so much easier on us to inspect...sheet metal screws for equipment ground connections(didn't have any bolts); #10 white for equipment ground (was out of green), Homeline breaker in a G0E panel (had it!), etc.

STUPID CODE!
:)
 
Re: NM in Liquidtite

Allen, just because your inspectors don't catch it doesn't change the fact that it is wrong.

especially when you had thhn from nm and it met ampacity
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THHN is not for wet locations, and besides, where is this information found that the conductors in NM are THHN or any specifc insulation type?


Roger
 
Re: NM in Liquidtite

Roger you have made a point that I try to make in the classes I teach.
334.112 Insulation.
The insulated power conductors shall be one of the types listed in Table 310.13 that are suitable for branch circuit wiring or one that is identified for use in these cables. Conductor insulation shall be rated at 90?C (194?F).
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The way that I read the above section is that NM cable could have RHH, THHN, XHH or any conductor from table 310.13 that is rated at 90 degrees.

:)
 
Re: NM in Liquidtite

"dang! I wish you guys could get that "didn't have it in the truck" exception added to all articles."
Now that is a broad statement.When it comes down to machine screws as opposed to illegal s/m screws that is a trip that has to be made.If a breaker isn`t listed to interchange again that trip has to be made.But nm is a perfectly adequate wiring method as long as it meets the needs and is listed.
Not sure about others ,but if I can avoid making an UNECESSARY trip that stops me from what I am doing to get something that is not necessary and I can finish with what I have and pass well to me that trip is useless.
 
Re: NM in Liquidtite

Well Wayne, remember this. Just because it passed is no relief in a law suit.
The thought that if it will pass I am going to do it has cost many an electrician in this state. Look here for more details about this way of thinking.
 
Re: NM in Liquidtite

"THHN is not for wet locations, and besides, where is this information found that the conductors in NM are THHN or any specifc insulation type"

Roger I stand corrected,I should have known that post would have come back to bite me.Yes again, you are correct since the conductors inside NM have no type printed on the insulation to say thhn is incorrect.I guess I heard it and it stuck "nm is thhn,nm is thhn,nm is thhn" :eek:

You are right I have never been tagged for it but I guess that the inspectors and myself don`t consider within LT as being in a wet location even outdoors.Because of the following.....

100 does state Wet location as being:Location underground or in concrete slabs or masonary in direct contact with earth,in locations subject to saturation with water or other liquids such as a vehicle washing areas
and in unprotected locations exposed to weather.
But, 334.12 d does say NM can`t be installed "Where exposed or subject to excessive moisture or dampness " That would hold up except that 356.10 (2) says LFNC is permitted Where protection of the contained conductors is required from vapors liquids or solids.
356.10 (3) says LFNMC is suitable for outdoor locations where listed and marked as suitable for the purpose.
So if LFNMCis listed as protection from vapors liquids or solids then the conductors within the LFNMC do not have to be rated as suitable for a wet location and the conductors that are from nm are ok to install in LFNMC.
If there is data to say otherwise let me know.
 
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