Wet locations, PVC and RX cable

[goldstar]

I know the NEC states that RX cable cannot be used inside PVC when installed outdoors. I'd just like to know the CMP's thinking in making this determination in some instances. Let's say you have an 40 amp AC disconnect located about 25' away from the breaker panel in a residence. You run 8/2 RX cable from the breaker panel, through the basement and directly into the back of the disconnect. The wiring INTO the disconnect is not considered a wet location but the wiring inside the fixture whip is. OK - no problem. Now let's say that you have to elevate the disconnect a bit to make it at a serviceable height. You install an LB stubbed into the basement and a terminal adapter and now that 8/2 RX cable is in considered to be in a wet location.

In another instance, you have to run a line for an AHU in the attic. You can't find a chase from the basement to the attic so you run the cable outside and sleeve it in a few lengths of PVC with an LB on each end stubbed into the attic and basement. The way I see it, unless you're in New Orleans during Hurricane Katrina and your house gets completely submerged, there's no way any water is getting inside that PVC. How can this be considered a wet location ?

To make matters worse, if you STUB PVC into a location (technically speaking) you need to have a cable fitting to hold the cable you've just installed. That means you'll have to install a PVC-female adapter and an RX connector to clamp onto the cable. That way the cable is properly terminated at both ends of the PVC.

I know this can all be Code compliant if you use just UF cable but IMHO it just adds more unnecessary $$ onto a job that you're trying to compete for.

BTW, we all know that the conductors inside RX cable are THHN but manufacturers don't mark the individual conductors. The wire rating is on the outer jacket. I think this is a scam perpetrated by wire manufacturers to get you to buy and stock more wire.

Sorry - just venting. An overwhelming majority of the NEC sections make sense but some don't IMHO.

 

[iwire]

It really just comes down to listings.

The inside of a raceway in a wet location is considered wet. This has been the case for a great many code cycles. Recently they have made changes to make this clear but it is not a new concept.

NM is not listed for wet locations so unless they decide to call the inside of a raceway in a wet location 'dry' we are stuck with how it is.

Can we honestly say with a straight face that outdoor raceways are dry inside?

I know I cannot, I find the large majority have water in the low spots.

 

[Dennis Alwon]

I agree with both of you. The NEC clearly prohibits however there must be a million a/c units done with NM cable or stripped wire from the cable. I doubt there will ever be a problem based on the wire in those situations. Certainly underground adds a different situation to the story.

I am curious how long it would take thhn- no W- was installed in water, to break down. My guess is a long time however the NEC will try and protect for those possibly unusual situations.

 

[infinity]

Since almost every modern THHN conductor is also THWN rated can't they just make NM cable with dual rated conductors?

 

[iwire]

The NEC clearly prohibits however there must be a million a/c units done with NM cable or stripped wire from the cable. I doubt there will ever be a problem based on the wire in those situations. Certainly underground adds a different situation to the story.

I am curious how long it would take thhn- no W- was installed in water, to break down. My guess is a long time however the NEC will try and protect for those possibly unusual situations.

And I agree with with you as well.

In my opinion this is a situation where the words in the NEC do make sense but do not not necessarily match what works fine in the real world. (I know, that sounds contradictory)

 

[iwire]

Since almost every modern THHN conductor is also THWN rated can't they just make NM cable with dual rated conductors?

They could, but you would still have to get the listing and code sections changed to allow NM in wet locations and considering they make UF for that I do not see that happening for NM.

 

[kwired]

I know the NEC states that RX cable cannot be used inside PVC when installed outdoors. I'd just like to know the CMP's thinking in making this determination in some instances. Let's say you have an 40 amp AC disconnect located about 25' away from the breaker panel in a residence. You run 8/2 RX cable from the breaker panel, through the basement and directly into the back of the disconnect. The wiring INTO the disconnect is not considered a wet location but the wiring inside the fixture whip is. OK - no problem. Now let's say that you have to elevate the disconnect a bit to make it at a serviceable height. You install an LB stubbed into the basement and a terminal adapter and now that 8/2 RX cable is in considered to be in a wet location.

Instead of installing an LB you can use an enclosure suitable for splicing and then you have a compliant install. Don't tell me it is ugly, the discussion is about compliance. If you wanted to avoid ugly you would have tried to avoid the LB in the first place.

In another instance, you have to run a line for an AHU in the attic. You can't find a chase from the basement to the attic so you run the cable outside and sleeve it in a few lengths of PVC with an LB on each end stubbed into the attic and basement. The way I see it, unless you're in New Orleans during Hurricane Katrina and your house gets completely submerged, there's no way any water is getting inside that PVC. How can this be considered a wet location?

I can promise you in most of the US you will get condensation in that raceway at some time.

To make matters worse, if you STUB PVC into a location (technically speaking) you need to have a cable fitting to hold the cable you've just installed. That means you'll have to install a PVC-female adapter and an RX connector to clamp onto the cable. That way the cable is properly terminated at both ends of the PVC.

If the raceway is just a sleeve where does it say the cable needs secured to the sleeve?
If the raceway is indeed installed as a 'raceway' it must be continuous from enclosure to enclosure - you will not be having any exposed cable in that instance.

I know this can all be Code compliant if you use just UF cable but IMHO it just adds more unnecessary $$ onto a job that you're trying to compete for.

Your competition is up against the same problems, unless they are not installing according to codes.

BTW, we all know that the conductors inside RX cable are THHN but manufacturers don't mark the individual conductors. The wire rating is on the outer jacket. I think this is a scam perpetrated by wire manufacturers to get you to buy and stock more wire.

Actually if they marked the conductors with proper information nothing would stop you from stripping sheath and using them as THHN/THWN or whatever they are marked with. Outer sheath of NM is not as durable as outer sheath of other kinds of cable - this could be some of reasoning, as well as reason why NM typically has more limitations on where it can be used than other types of cable. It may be more of a listing issue than manufacturers making you buy more kinds of cable for different applications. You also need to remember when it comes to wet locations NM cable has absorbent paper linings where other types of cables don't.

 

[goldstar]

Since almost every modern THHN conductor is also THWN rated can't they just make NM cable with dual rated conductors?

They do. They just don't mark the individual conductors as such. That's why you can't strip the jacket off and use those conductors inside the whip. That's why, IMO I think there are wire manufacturers who make up parts of the CMP's who make these rules. I could be wrong but I'd bet a buck I'm not.

 

[kwired]

They do. They just don't mark the individual conductors as such. That's why you can't strip the jacket off and use those conductors inside the whip. That's why, IMO I think there are wire manufacturers who make up parts of the CMP's who make these rules. I could be wrong but I'd bet a buck I'm not.

I think it is listing problem more than a code problem to use the conductors without the sheath.

 

[goldstar]

I can promise you in most of the US you will get condensation in that raceway at some time.

I'll have to take your word on that. Do you think there would be enough condensation to fill up the conduit in the instances that I cited and cause wicking or water damage to the RX cable ? I don't see that happening.

If the raceway is just a sleeve where does it say the cable needs secured to the sleeve?

If you're sleeve RX cable into EMT you're suppoosed to use a "from-to" connector to hold the cable. According to many inspectors I come in contact with the same logic applies with respect to sleeving into PVC. If you stop and think about it, the RX cable that I cited in the case where an LB was used, is not properly terminated into the disconnect. It came through a PVC-TA with no clamp. I can't imagine what could possibly happen to that cable seeing as how it is properly supported in the basement but the fact is - it is not properly terminated at the disconnect end.

Your competition is up against the same problems, unless they are not installing according to codes.

You are 100% correct if we are going to ASSUME that everyone is playing by the same rules. But, you can have 2 high quality contractors installing similar jobs. One will use UF and the other NM. One will file a permit, get inspected and pass that inspection and the other will not file a permit and will not get inspected. The homeowner who's contractor used UF cable and got plumbing. building and electrical inspections for his AC system, will have probably paid $1K more for his installation than his neighbor did. Both got installations that will work safe and properly for many years. It would be great if there were an honesty system in place everyone would just go out and get permits but that's noit the real world.

Actually if they marked the conductors with proper information nothing would stop you from stripping sheath and using them as THHN/THWN or whatever they are marked with. Outer sheath of NM is not as durable as outer sheath of other kinds of cable - this could be some of reasoning, as well as reason why NM typically has more limitations on where it can be used than other types of cable. It may be more of a listing issue than manufacturers making you buy more kinds of cable for different applications. You also need to remember when it comes to wet locations NM cable has absorbent paper linings where other types of cables don't.

I don't see how the paper inside the NM could wick in either of the examples I cited. However, if you're telling me that condensation could wick right through the jacket around the NM cable inside the PVC sleeve then I'll take your word for it.

When you look at the situation our economy is in, with lack of jobs and construction going on, etc. my gripe with this is that we're going to end up with more and more EC's taking the short cut (even if it's not code compliant) by running the NM. Why can't the wire manufacturers make a cable that can be used for both indoor and outdoor use ? MC cable is made with a plastic wrapping around the conductors before the aluminum spiral jacket goes on. Why can't NM be made the same way ?

I'll get off the soap box now.

 

[goldstar]

I think it is listing problem more than a code problem to use the conductors without the sheath.

I'm sure you're correct.

 

[frankft2000]

I was recently wondering what the insulation type was of the conductors inside UF cable, since they are not marked. I guess the inside of UF cable must be considered a "dry location"!

 

[kwired]

Do you think there would be enough condensation to fill up the conduit in the instances that I cited and cause wicking or water damage to the RX cable ?

How much condensation depends on conditions. You would be suprised how fast it can build up if the raceway is arranged so that it "traps" water in it. I don't know how easily it will damage NM cable.

I don't see that happening.If you're sleeve RX cable into EMT you're suppoosed to use a "from-to" connector to hold the cable. According to many inspectors I come in contact with the same logic applies with respect to sleeving into PVC. If you stop and think about it, the RX cable that I cited in the case where an LB was used, is not properly terminated into the disconnect. It came through a PVC-TA with no clamp. I can't imagine what could possibly happen to that cable seeing as how it is properly supported in the basement but the fact is - it is not properly terminated at the disconnect end.

Please provide code references - I am not finding any that support what you are suggesting. If the "sleeve" is essentially an extension of an enclosure - maybe it needs secured. If it is truly a "sleeve" with cable exiting each end I see no requirement that it be secured to the "sleeve"

You are 100% correct if we are going to ASSUME that everyone is playing by the same rules. But, you can have 2 high quality contractors installing similar jobs. One will use UF and the other NM. One will file a permit, get inspected and pass that inspection and the other will not file a permit and will not get inspected. The homeowner who's contractor used UF cable and got plumbing. building and electrical inspections for his AC system, will have probably paid $1K more for his installation than his neighbor did. Both got installations that will work safe and properly for many years. It would be great if there were an honesty system in place everyone would just go out and get permits but that's noit the real world.

That is reality of the world we live in. You will run into that with just more than NM vs UF situations. Anyone not pulling permits when required has a good shot at underpricing anybody, they will be able to do the job to different standards than those who do file permits when required - unless they get caught. Pull permit for job before you are awarded the work. If you don't get the job AHJ is involved because you pulled a permit - they will want to know if the job is still being done and who is doing it - you just opened a can of worms for the guy that thought it would be an easy job(just an idea).

When you look at the situation our economy is in, with lack of jobs and construction going on, etc. my gripe with this is that we're going to end up with more and more EC's taking the short cut (even if it's not code compliant) by running the NM. Why can't the wire manufacturers make a cable that can be used for both indoor and outdoor use ? MC cable is made with a plastic wrapping around the conductors before the aluminum spiral jacket goes on. Why can't NM be made the same way ?

People take short cuts in all kinds of trades or professions - especially when times are harder. If you want to do the job right you need emphasize selling that and not price alone, some will get away, others will be a catch. Those you do catch may very well be more pleasant to work for than those that only care about price. Those that only care about price will agree to a price and then will still complain about anything they can to try to get more of a break.

We do have a non metallic sheathed cable for indoors and outdoors and it was mentioned - it is called UF cable.

I was recently wondering what the insulation type was of the conductors inside UF cable, since they are not marked. I guess the inside of UF cable must be considered a "dry location"!

The conductors inside the cable were not intended to be used in any other way except for as part of the cable - that is why they are not marked. They may or may not be same thing as THHN/THWN, but the fact they are not marked means they are not a conductor listed in 310.104 and are not designed to be used without the rest of the assembly they are a part of.

NM is a dry location only cable. UF is for wet or dry locations, as well as direct burial. In both cases this is for the entire assembly as a whole not just the inside or outside.

 

[goldstar]

Please provide code references - I am not finding any that support what you are suggesting. If the "sleeve" is essentially an extension of an enclosure - maybe it needs secured. If it is truly a "sleeve" with cable exiting each end I see no requirement that it be secured to the "sleeve"

I can't find a code section for using a "from-to" connector when sleeving NM inside EMT. The closest I can come to it is 300.15(C) and 300.19(C). When you have a complete wiring system where raceways are terminated on both ends using JB's, the individual conductors inside the raceway are considered properly terminated. When you have a cable assembly (like RX cable) that you pass through a raceway, when using that raceway as a protective sleeve, using an LB and a terminal adapter does not properly terminate that cable assembly (technically speaking).

 

[goldstar]

Here's something I wasn't aware of regarding "stubbing" into basements and attics :

300.7 Raceways Exposed to Different Temperatures.
(A) Sealing. Where portions of a raceway or sleeve are
known to be subjected to different temperatures, and where
condensation is known to be a problem, as in cold storage
areas of buildings or where passing from the interior to the
exterior of a building, the raceway or sleeve shall be filled
with an approved material to prevent the circulation of
warm air to a colder section of the raceway or sleeve. An
explosionproof seal shall not be required for this purpose.

How could someone possibly know if condensation is going to be a problem in the cases I cited ?

 

[Dennis Alwon]

Here's something I wasn't aware of regarding "stubbing" into basements and attics :

300.7 Raceways Exposed to Different Temperatures.
(A) Sealing. Where portions of a raceway or sleeve are
known to be subjected to different temperatures, and where
condensation is known to be a problem, as in cold storage
areas of buildings or where passing from the interior to the
exterior of a building, the raceway or sleeve shall be filled
with an approved material to prevent the circulation of
warm air to a colder section of the raceway or sleeve. An
explosionproof seal shall not be required for this purpose.

How could someone possibly know if condensation is going to be a problem in the cases I cited ?

I have done many stubs from a crawl space to an attic and to my knowledge condensation has never been an issue. I wonder what temp difference is needed to create condensation?

 

[goldstar]

I have done many stubs from a crawl space to an attic and to my knowledge condensation has never been an issue. I wonder what temp difference is needed to create condensation?

I've never had this problem either but apparently some contractors have. Again, I know the NEC states that if a PVC conduit is installed on the outside of a house, irrespective of whether it is stubbed into the structure or not, the inside if that conduit is considered a wet area. I know what's written, I can read like everyone else. I just can't understand the logic in making this rule in the cases I cited in the OP. If the conduit is considered to be in a wet area why isn't the disconnect treated the same way ? You're permitted to enter the back of a disconnect with NM from inside the house but if you use an LB (approx 6") and a terminal adapter (approx. 1") to raise the disconnect height to a servicable distance you're in violation. Go figure !

 

[K8MHZ]

Could someone please tell me what RX cable is?

 

[kwired]

Here's something I wasn't aware of regarding "stubbing" into basements and attics :

300.7 Raceways Exposed to Different Temperatures.
(A) Sealing. Where portions of a raceway or sleeve are
known to be subjected to different temperatures, and where
condensation is known to be a problem, as in cold storage
areas of buildings or where passing from the interior to the
exterior of a building, the raceway or sleeve shall be filled
with an approved material to prevent the circulation of
warm air to a colder section of the raceway or sleeve. An
explosionproof seal shall not be required for this purpose.

How could someone possibly know if condensation is going to be a problem in the cases I cited ?

I've never had this problem either but apparently some contractors have. Again, I know the NEC states that if a PVC conduit is installed on the outside of a house, irrespective of whether it is stubbed into the structure or not, the inside if that conduit is considered a wet area. I know what's written, I can read like everyone else. I just can't understand the logic in making this rule in the cases I cited in the OP. If the conduit is considered to be in a wet area why isn't the disconnect treated the same way ? You're permitted to enter the back of a disconnect with NM from inside the house but if you use an LB (approx 6") and a terminal adapter (approx. 1") to raise the disconnect height to a servicable distance you're in violation. Go figure !

If there is temperature difference at each end of raceway condensation is very likely. The more humidity exists the more likely it becomes. Warm moist air is going to condense if the temperature drops. In many areas we see this almost daily every morning with the dew on the grass. The overnight cooling was enough the air could no longer contain the moisture it was holding and it is given up as condensation. This happens in nearly every outdoor raceway. It happens in cold climates when a raceway enters a building, you have warm moist air inside and cold air outside. Migration of that warm moist air through the raceway condenses as it is cooled. Same thing with a raceway entering a refrigerated space.

This is nothing new, you just have never noticed or had it pointed out to you.

You ever seen conductors entering an outdoor enclosure from directly above a main breaker, and the terminals look like they have had water on them? It was from condensation running down the raceway and following conductors to the terminals. Avoiding having conductors run straight to terminals helps prevent this. Give the conductors a "drip loop" if possible. Sealing the raceway doesn't help much as any condensation is still going to accumulate at bottom and likely make it through the seal eventually. Sealing a raceway that enters a building does prevent two different temperatures on opposite ends of the raceway from causing condensation though.

 

[kwired]

Last summer I remember burying PVC conduit in the ground on a Friday. It was a hot humid day. On Monday we came back to pull conductors. There was no rain over the weekend, and it was not excessively moist soil conditions, yet the rope we pulled conductors with was wet when pulled out. Where did that kind of water come from in just a couple days when there was no rain? Condensation.