Cable thru return vent

[GerryB]

I am doing the wiring for a customer for central air in her house. So I'm in the attic trying to fish the t-stat wire and the AC guy is cutting the return vent for the hallway. He had drilled a couple of pilot holes and when he moved the insulation there were 2 bx cables running through the joists right where his return was going. He was staring at them so I said something like "oh right were you need to go" . He said it was no big deal though. Then he went ahead and notched his vent around the cables. Is that a violation? I know I have seen older homes where they put sheet metal over basement ceiling joists for returns with wires running through them.

 

[retire09]

See 300.22(c) and exception
(C) Other Spaces Used for Environmental Air (Plenums).
This section shall apply to spaces not specifically
fabricated for environmental air-handling purposes but used
for air-handling purposes as a plenum. This section shall
not apply to habitable rooms or areas of buildings, the
prime purpose of which is not air handling.
Exception: This section shall not apply to the joist or stud
spaces of dwelling units where the wiring passes through
such spaces perpendicular to the long dimension of such
spaces.

 

[kwired]

How they run through the "plenum" makes a difference, as retire09 quoted the applicable section - if they pass perpendicular through the space they are likely just fine. If that is not the case can they be enclosed somehow to make them "outside" the plenum?

Also if you read a little farther down in (C)(1) - the AC cable may be permitted even if not just running perpendicular to the space if it is:

"Type MI cable without an overall nonmetallic covering, Type MC cable without an overall nonmetallic covering, Type AC cable, or other factory-assembled multiconductor control or power cable that is specifically listed for use within an air-handling space, or listed prefabricated cable assemblies of metallic manufactured wiring systems without nonmetallic sheath" (copied from within (C)(1))

If it is an old AC cable it probably isn't listed for such space, newer cable - maybe, MC cable says is acceptable as long as it doesn't have a nonmetallic covering.

 

[GerryB]

Thanks for the replies. What I've seen in the past was cables perpendicular through joists being used as cold air returns, the Code Handbook had a picture of it as ok. This here since it is "specifically fabricated for environmental air" it's probably a violation but not the end of the world, although I'm sure he would have done the same thing if it was romex.

 

[electricman2]

I think someone posted on this topic before that if the temperature in that return is high enough to damage conductor insulation, then that is the least of their problems, there is something on fire somewhere!

 

[kwired]

Thanks for the replies. What I've seen in the past was cables perpendicular through joists being used as cold air returns, the Code Handbook had a picture of it as ok. This here since it is "specifically fabricated for environmental air" it's probably a violation but not the end of the world, although I'm sure he would have done the same thing if it was romex.

There is a difference between "specifically fabricated for environmental air" and "Other Spaces Used for Environmental Air".
One is covered by 300.22(B) and the other by 300.22(C). (B) prohibits any wiring inside unless it is necessary for the direct action upon, or sensing of, the contained air, (C) is what we have been talking about and can be wiring not associated with the contained air.

 

[GoldDigger]

There is a difference between "specifically fabricated for environmental air" and "Other Spaces Used for Environmental Air".
One is covered by 300.22(B) and the other by 300.22(C). (B) prohibits any wiring inside unless it is necessary for the direct action upon, or sensing of, the contained air, (C) is what we have been talking about and can be wiring not associated with the contained air.

IMHO, that includes the difference between a full metal duct which is located between floor joists and a return duct formed by fastening a sheet of metal between two joists to enclose the space.
The OP's mention of notching the duct around the wires makes it sound like the former. In which case I do not see it as permitted.
But there is a lot of room for AHJ interpretation in any case.

 

[kwired]

IMHO, that includes the difference between a full metal duct which is located between floor joists and a return duct formed by fastening a sheet of metal between two joists to enclose the space.
The OP's mention of notching the duct around the wires makes it sound like the former. In which case I do not see it as permitted.
But there is a lot of room for AHJ interpretation in any case.

I agree - and must say it is not entirely clear just what the OP has, but if the sheet metal was notched then there is a good chance it is a complete duct and not just a panned off space.

This is one of those code issues that sometimes doesn't entirely make sense if you look at the big picture.

Used to have an EI that when he encountered a panned off floor joist with NM cables passing perpendicular through it - he would count cables on each side - if there were not same number on each side you must have run one parallel inside the plenum - violation. When in reality there were some cases where if you turned the cable and went up a wall instead of pulling across the plenum you actually had less exposed cable inside the plenum, one of the reasons for the rule - yet he wouldn't pass you if it did not cross the plenum to the opposite side because that is how it is worded.