Romex in cold air return

[bradleymattlin]

Can someone explain 300.22. what is the difference of running romex thru thr return compared To only running four foot in the return. Iam just not the seeing the difference because the wire is in the return regards less. Thanks.

 

[S'mise]

Heres my take; The goal is to minimize toxic smoke from the plastic insulation or sheath burning off the wire/cable. Bad thing to have anything toxic getting into the air supply. An exception exists to run romex the short way across a joist (I dont think thats a good idea either) but you can never fish a romex cable thrugh unprotected the long way (which is done by inexperienced people because its an easy path) The 4ft rule is intended to run FMC to devices used for hvac stuff in the duct like dampers, air sensing, thermostats and such.

 

[bradleymattlin]

Thanks John. Makes sense

 

[kwired]

When it comes to panned off floor joists for return air and NM cables bored through same joists, I once had an inspector that had a theory that worked most of the time but still had some flaws. If there is a panned off joist with 4 cables entering one side then he assumes if they run straight across the space the same 4 cables will exit the other side. If 4 cables enter one side and only three exit the other side then the fourth one must be going parallel with the air movement. Here is where I had a problem with that approach. If four entered one side and only three exit the opposite side why can't the missing cable actually turn and go up a wall and maybe even have less exposed cable in the air space than the three that cross to the opposing side?

My other thought/question is are we not supposed to provide overcurrent protection which should prevent the cable from being the source of the heat necessary to produce the smoke? Sure fire could start from something else and spread to the cable at some point, but the house is full of all kinds of plastics that will give of toxic fumes when they burn, and they are likely to kill you long before the burning sheath of what is likely a limited amount of cables. Plumbers and others will put plastics in air handling spaces and nobody mentions anything about those? I don't know the burning characteristics of flex duct, but it is likely nasty fume producing if it does burn.

Anyway, I just try as much as possible to avoid air handling space with NM cable, then you have no problem with your installation to start with.

 

[GoldDigger]

My other thought/question is are we not supposed to provide overcurrent protection which should prevent the cable from being the source of the heat necessary to produce the smoke? Well, if the OCPD also provides arc fault protection, then yes. But that is a whole different thread.

Plumbers and others will put plastics in air handling spaces and nobody mentions anything about those? Somebody probably should. I suspect that it is not code except for certain types of pipe.

I don't know the burning characteristics of flex duct, but it is likely nasty fume producing if it does burn. I'll have to look into that one!

Anyway, I just try as much as possible to avoid air handling space with NM cable, then you have no problem with your installation to start with.
That also takes care of people who go through the sheet metal itself and do not provide bushings.

Comments inline.

 

[kwired]

Quoting quotes is a pain sometimes.

My other thought/question is are we not supposed to provide overcurrent protection which should prevent the cable from being the source of the heat necessary to produce the smoke?Well, if the OCPD also provides arc fault protection, then yes. But that is a whole different thread. Agree, but will add I had this opinion before we even heard of AFCI's

Plumbers and others will put plastics in air handling spaces and nobody mentions anything about those? Somebody probably should. I suspect that it is not code except for certain types of pipe. Very possible, now come to where I live where electrical is about all that is inspected - especially in dwellings. Most other trades do not respect the fact the electricians have to pass an inspection and don't care what they do that may make it more difficult for the electrician, as long as their job is easier anything goes.

I don't know the burning characteristics of flex duct, but it is likely nasty fume producing if it does burn. I'll have to look into that one!

Anyway, I just try as much as possible to avoid air handling space with NM cable, then you have no problem with your installation to start with.
That also takes care of people who go through the sheet metal itself and do not provide bushings. And the HVAC guys that slot a piece of tin to go around a cable. Most are using foil backed non metallic panning materials anymore so that is not as much of a problem. Still what is the burning characteristics of that? They probably are fire retardant, but not fire proof. Isn't NM sheath fire retardant but not fire proof also?

 

[hudsonvalleyelectrician]

Romex in what are now return air ducts/plenums

Romex in what are now return air ducts/plenums

I wired a whole house, got my rough in inspection. Came back a month later to start the trim out and lo and behold the homeowner had made the decesion to install central A/C, it was 75% done and there were tin return thingys covering at least four sections of joists in the basement. Boy was I pissed, I mentioned we might have a problem due to the romex running both prependicular and long ways and was dismissed, no changes were made, work progressed. I have been doing research ever since. I have to say I am worried about the eventual final inspection.

 

[GoldDigger]

I have to say I am worried about the eventual final inspection.

I hope the inspector realizes it was not your decision and does not give you a hard time on later inspections because of it.
But if you have to sign off on it before inspection, it is still your reputation on the line.
Best case he will not notice and there will not be any problems with the house that need later electrical work in the area.

 

[kwired]

I wired a whole house, got my rough in inspection. Came back a month later to start the trim out and lo and behold the homeowner had made the decesion to install central A/C, it was 75% done and there were tin return thingys covering at least four sections of joists in the basement. Boy was I pissed, I mentioned we might have a problem due to the romex running both prependicular and long ways and was dismissed, no changes were made, work progressed. I have been doing research ever since. I have to say I am worried about the eventual final inspection.

I hope the inspector realizes it was not your decision and does not give you a hard time on later inspections because of it.
But if you have to sign off on it before inspection, it is still your reputation on the line.
Best case he will not notice and there will not be any problems with the house that need later electrical work in the area.

Here is where we get into differences in AHJ's. The installer did nothing wrong, but conditions changed after the fact. Good AHJ's are still going to acknowledge that it was not the installers fault, but also are not going to leave a known violation. It should in no way effect inspections of future work.

My suggestion, pull down the tinned off sections (if necessary) that are a problem and either reroute what you can or enclose what can't be moved somehow so that it is no longer in the environmental air space. The NM cable can't be in the 'duct', but another enclosed space containing the NM cable can be in the 'duct'.

If owners refuse to have you make necessary changes then maybe AHJ needs to get involved in convincing them to change. Failure to pass inspection often works.