Can I (should I) run a 2 inch PVC pipe and a low voltage wire between 2 studs that are used as part of the cold-air return system? This would be for a central vac outlet.
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That seems to be SOP around here for retro-fitting central-vac into a home.
Phill Giles
The Unionville Woodwright
Unionville, Ontario
Crazy as it sounds, the low voltage wire has to be plenum rated.
Dave
Why if in a return? What if you ran it through conduit?
I wish I knew the answer to that one. We run into it all the time at work. Even the LAN and coax have to be plenum rated. Everything above our drop ceiling is in the return air plenum.
If this is a retro for a new central vac in an old house, I would just tape it to the side of the pipe and let it go. If it is new work, the inspectors here won't let it go. They don't really want anything in the return air plenum, but will allow a run of conduite, or rate wire. I have found it best to have the spool, with the label on it, setting nera the questionable area.
Dave
> Crazy as it sounds, the low voltage wire has to be plenum rated.
I was under the impression (though I may be wrong) that the NEC allowed you to run non-plenum cable ACROSS a duct, taking the shortest route. If you try to run the cable THROUGH the duct, though, it must be plenum rated.
This is one of those code sections that takes 8 paragraphs to tell you not to do something, and then throws in an exception that says OK go ahead and do it anyway.
I see the same thing on new commercial jobs that Dave is talking about.Most HVAC designers don't call for return air ducting but use the area above lay in ceilings as a plenum.Whatever cabling we run,telephone,Cat5 data,thermostat,fire alarm,and HVAC controls all have to be plenum rated cable,and the inspectors do check it.In case of a fire I guess it yields less toxic smoke that would be pumped into the building before the fan shutdown kicks in.
But after the Code details only using metallic conduits and listed cabling in environmental air spaces ,then it says if you're passing through a dwelling joist space perpendicular to the long dimension it's OK.I guess everybody gets to decide how high to set the bar for their house.