NM cable and the outdoors

[Nuber]

The manufacturers had nothing to do with 300.9. 300.9 was a code change proposal of mine to clear up the question as to whether the inside of a raceway installed in a wet location is also a wet location. CMP-3 acted on my proposal and said that the inside of such a raceway is indeed a wet location.

In this case we now know it wasn't. In the field blaming the manufacturers for something that may not make initial sense is a common practice - probably rarely true in actuality.

Conceptually I still have issue with requiring the inside of a raceway, on the side of a building, with raintite fittings, all components installed to code, being called a wet location.

Perhaps being in a dry state like Colorado has affected my perception in comparison to moist southern and eastern states, but out here if you install a conduit on the side of a building with raintite fittings, there isn't any moisture inside the conduit unless you put it there or the installation failed in some way.

In practice this whole debate doesn't mean a whole lot for me, I don't like installing NM in a raceway anyway. Hard to pull, takes up way too much space, don't want to argue with inspectors as a general principle.

Thanks for contributing to my knowledge tool kit, thanks for helping to improve the code.

 

[Dennis Alwon]

Nuber, what you don't seem to realize is that there is condensation in conduit installed outdoors. Raintight fittings and all will not keep the inside of the raceway dry. Whether it is a real issue or not is not my argument but I felt the need to throw this out there

 

[Buck Parrish]

Seems to be consensus so far. My question then -

What use are raintite fittings for EMT and the like? They serve no purpose whatsoever other than to increase the cost of the installation.

You're some what right about that. Our thoughts were that if water gets in and freezes it will expand and destroy the pipe. But if condensation already is in, then the water of course is already in. Perhaps the raintight fitting could help to keep it out.

 

[K8MHZ]

Raintight keeps _most_ rain water out. Condensation enters as vapor and raintight fittings don't even slow that down. In fact, they may keep more water in, than out.

 

[Fred B]

One thing that seems to always get mixed: Rain tight is not the same as watertight, 2 different criteria.

 

[Nuber]

Nuber, what you don't seem to realize is that there is condensation in conduit installed outdoors. Raintight fittings and all will not keep the inside of the raceway dry. Whether it is a real issue or not is not my argument but I felt the need to throw this out there

Perhaps - as referenced I have most frequently worked in a very dry state. I personally don't see any significant moisture trapped in the raceway. This is not a scientific statement, just an observation. I fully understand that air contains moisture and condensation is a real effect. If air and the associated condensation makes for a wet location, then why is the inside of a NEMA 3 enclosure not considered a wet location? The air was trapped inside there as well.

The code makes distinctions between damp and wet locations and in my experience underground is without a doubt wet, above ground on the side of a building is not. (this is a real world statement - as discussed earlier 300.9 makes this a wet location according to the code) I have installed and worked on existing installation with both compression and raintite fittings on buildings. In my experience I see no difference for the wire. I concede that Floridian electricians may have a different experience - and perhaps that is the true answer.

In any case this was a good code exercise. Thanks to all.

 

[Fred B]

AFA NM on or in wet/damp area the paper inside will wick water (or other liquids) a long way up into the sheathing, once wet it comprises the insulation and heat dissipation ability, thus the requirements. I've seen someone install for exterior (side of house wall for sconces) and water wicked more than 2ft uphill and where they went straight into basement, all the way to jbox, more than 10ft. Just from improperly sealed fixture, and another from exposed run pre fixture installation, could actually wring water from the paper.

 

[all-power]

Article 100 defines Wet locations as in "unprotected locations exposed to weather". If wires in conduit are not protected then can someone tell me what is considered protected? To consider the inside of a conduit a wet location on the side of a house is crazy. Where do you stop. Every time you open the door to your house you expose the inside to the outside elements. Does that make it a wet location? Windows can be left open and water can get in. Does that make it a wet location. Think about what you are saying. Water tight fittings, water tight box, metal conduit is a wet location.

 

[macmikeman]

Not true. Some places will not allow a panel on the outside of a house because there is no way to bring the NM home runs into it that satisfies the Code.

-Hal

I don't think so. Here is why. Manufactures printed instructions over NEC codes per the NEC. Now look at the roll of NM cable with the plastic package it came in. It says " indoors". A 3r rated panel has a door. I rest my case Your Honor..........................

 

[Fred B]

Article 100 defines Wet locations as in "unprotected locations exposed to weather". If wires in conduit are not protected then can someone tell me what is considered protected? To consider the inside of a conduit a wet location on the side of a house is crazy. Where do you stop. Every time you open the door to your house you expose the inside to the outside elements. Does that make it a wet location? Windows can be left open and water can get in. Does that make it a wet location. Think about what you are saying. Water tight fittings, water tight box, metal conduit is a wet location.

Refer to definition of dry area or damp area should clear up "unprotected", see also informational note for damp location
Whether you consider it crazy or what ever, the code says what it says.
NEC 2017, 300.9, says it's a wet area if installed in a location considered to be a wet area and the inside of the conduit or raceway is considered a wet area if installed in such location.
310.10(C)(3) says wire must be listed for use in wet areas,
334.10(B)(4) says NM is not to be to be used in wet or damp locations.
300.9 gives NO exception as to watertight fittings, boxes, or for metal conduit.
Code is the code, we don't write it just live by it. If you don't like it submit proposal for a code change.

One thing not clear, and doesn't make sense, is no mention or clearification of interior of box or enclosure. So can one assume that the interior of the conduit connected to a box is wet but the box is not? So if a conduit was to continue from that box to another box it is again a wet area? Maybe someone associated with the code panel can clarify.

 

[petersonra]

I think it's moderately bizarre then an outside box is not a wet area but the conduit leading into and out of it is.

 

[readydave8]

To consider the inside of a conduit a wet location on the side of a house is crazy.

I'm always surprised when I pull wires out of pipe and they're dry

 

[GoldDigger]

The concern is not water entering the conduit at fittings, it is condensation of moist air inside the conduit when outside temperatures are low. It will generally be noticeable in winter if one or both ends open into heated and humidified interior space.
The Code is using a broad prohibition instead of a much more complicated condition possibly requiring testing or an engineering evaluation.

A four inch stub from an exterior wall mounted box is not likely to see much condensation.

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[kwired]

You might want to take a look at 300.9.

Yet we have to use those @$^&% rain tight fittings.

More water finds its way inside from condensation than a standard compression fitting will ever let in most cases.

Seen set screw fittings in places they really shouldn't be that still did a fair job keeping water out at times. Open the enclosure expecting the worst and everything looks almost new inside, must not have leaked much if any at all.

 

[kwired]

I'm always surprised when I pull wires out of pipe and they're dry

Hot summer day they often will be unless underground raceways.

 

[kwired]

The concern is not water entering the conduit at fittings, it is condensation of moist air inside the conduit when outside temperatures are low. It will generally be noticeable in winter if one or both ends open into heated and humidified interior space.
The Code is using a broad prohibition instead of a much more complicated condition possibly requiring testing or an engineering evaluation.

A four inch stub from an exterior wall mounted box is not likely to see much condensation.

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I work on grain storage bins a lot. usually dealing with steel raceways whether RMC/IMC or EMT, PVC usually underground but little if any above ground. If you ever come back to do modifications or for service calls, there is almost always signs of condensation having occurred, even if it is completely dry while you are there. If you don't "arrange to drain" things fill up, rust out, freeze and split open in winter, etc.

I always drill weep holes in just about every enclosure that doesn't naturally have drainage methods.

Come back to change a receptacle, if no weep hole often bottom mounting screw is rusted in and sometimes won't come out at all. Lower end of receptacle may be compromised as well. Box with weep hole is usually in good condition and no problems taking apart.

Daily heat -cool cycling is often enough to get at least some condensation almost daily around here. Maybe in southwest US it isn't that bad, but I bet it still happens at times.

 

[all-power]

Refer to definition of dry area or damp area should clear up "unprotected", see also informational note for damp location
Whether you consider it crazy or what ever, the code says what it says.
NEC 2017, 300.9, says it's a wet area if installed in a location considered to be a wet area and the inside of the conduit or raceway is considered a wet area if installed in such location.
310.10(C)(3) says wire must be listed for use in wet areas,
334.10(B)(4) says NM is not to be to be used in wet or damp locations.
300.9 gives NO exception as to watertight fittings, boxes, or for metal conduit.
Code is the code, we don't write it just live by it. If you don't like it submit proposal for a code change.

One thing not clear, and doesn't make sense, is no mention or clearification of interior of box or enclosure. So can one assume that the interior of the conduit connected to a box is wet but the box is not? So if a conduit was to continue from that box to another box it is again a wet area? Maybe someone associated with the code panel can clarify.

That's my point. dry box to dry box using conduit and the conduit is wet. People tend to look to much into the code. NM wire is permitted in normally dry locations. Normally means that most of the time it is dry but if it gets wet or damp sometimes that is ok.

 

[Fred B]

That's my point. dry box to dry box using conduit and the conduit is wet. People tend to look to much into the code. NM wire is permitted in normally dry locations. Normally means that most of the time it is dry but if it gets wet or damp sometimes that is ok.

But that is not what 334.10(B)(4) says. It states that NM shall not be used in wet or damp locations.

 

[all-power]

Again look at the def of wet location. The only thing there is there could be moisture in the conduit. However, then you would not be able to use NM in a bathroom with a shower. Just think of how much moisture a bathroom gets. Especially when my daughter uses it. There is no code for the level of moisture and moisture will also depend on your geographic location. Romex used to have on the package that the wire insulation were THHN/THW rated. I can't find anything now.

 

[Fred B]

Again look at the def of wet location. The only thing there is there could be moisture in the conduit. However, then you would not be able to use NM in a bathroom with a shower. Just think of how much moisture a bathroom gets. Especially when my daughter uses it. There is no code for the level of moisture and moisture will also depend on your geographic location. Romex used to have on the package that the wire insulation were THHN/THW rated. I can't find anything now.

A definition does not supersede a specific code section(s) ie: 300.9 and 334.10(B)(4).

It's not about the conductors type, same conductors are used in UF, it's the paper insulation inside under sheath and around ground conductor will wick moisture and will compromise the insulating and cooling of the conductors, and particularly if contaminants are present ie flood, can break down the insulation.