As Seen on This Old House

Status
Not open for further replies.
tom baker

tom baker

First Chief Moderator & NEC Expert
Staff member
Location
Bremerton, Washington
Occupation
Master Electrician
A recent episode of This Old House had the plumber, Richard, discussing a new damper (for heating ducts) control system that used what appeared to be RJ11 jacks and phone cords to plug into the control panel and damper. What got my attention was in cases where the duct was not accessible a damper is dropped into the outlet in place of a floor grate and wire is run thru the inside of the hot air supply duct, or plenum.
I didn't catch who the manufacturer was.
 
That idea has been around for a long time using pneumatic tubing and expandable bags. I guess this is just a newer approach. Certainly easier to conceal wire than tubing though I question the reliability of RJ connectors in this application. I can't see why screw terminals and thermostat wire wasn't used- oh wait, I do know- plumbers.

-Hal
 
I did some new construction last year that had a whole house management system similar, dampers installed on every run, however the RJ and blocks were strapped to the ouside of the duct, and from what I understood, they're only used when first setting up the system and balancing, but abandoned in the field. Wonder if these were similar/pulled out after the fact?
 
Mgraw said:
It is probably a Zonefirst 12v dc system.
Click to expand...

In my case, I'm sure it wasn't one of these, as we had discussed this in detail with the HVAC guys, they said it was only for the initial system commissioning and then once the system was balanced, everything was abandoned in place and the dampers were dogged in position.
 
So from a code compliance standpoint my questions are #1 if the cables are actually abandoned are they removed or tagged to be code copliant. and #2 are the ones that actually run in the ducts plenum rated etc.?

There are some fuzzy areas here and I doubt that most AHJs would catch any of this from my experiance (I have seen other contractors run NM cable and LV cabling through cold air returns without getting red flagged on new residential installs), but it would be great to hear from some actual inspectors about their veiws on this.
 
You can't run plenum in ducts anyhow, or at least that's how it's been interpreted in the code here. I'm sure there's some "creative" folk out there. Only way I've known as a compliant method would be to run wiring through ducts is using conduit or flex.

A return is one thing, but supply is a no-no.
 
Zonefirst says you can run their plenum rated power cords in the duct. I believe code says the only wires allowed in ducts is wiring associated with system components. I think power dampers would be included in system components.
 
Mgraw said:
Zonefirst says you can run their plenum rated power cords in the duct. I believe code says the only wires allowed in ducts is wiring associated with system components. I think power dampers would be included in system components.
Click to expand...

They would hardly be the first manufacturer to tell you you can do something the NEC prohibits. If their power cords are non-metallic, I'm pretty sure you can't put them "naked" in supply or return. The plenum rating is for use in "other environmental air spaces" such as the cavity above suspended ceilings when used as an air return.
 
Mgraw said:
Zonefirst says you can run their plenum rated power cords in the duct. I believe code says the only wires allowed in ducts is wiring associated with system components. I think power dampers would be included in system components.
Click to expand...
While the cable is directly associated with something that is in the duct, this would be a 300.22(B) application and cable is not permitted unless it has an outer non-metallic jacket.
 
del91574 said:
You can't run plenum in ducts anyhow, or at least that's how it's been interpreted in the code here. I'm sure there's some "creative" folk out there. Only way I've known as a compliant method would be to run wiring through ducts is using conduit or flex.

A return is one thing, but supply is a no-no.
Click to expand...

That was my point wiring is not allowed inside the duct. NEC does allow it where necessary to act on the air inside. Typically that is a sail switch or smoke detector.
 
WIMaster said:
There are some fuzzy areas here and I doubt that most AHJs would catch any of this from my experiance (I have seen other contractors run NM cable and LV cabling through cold air returns without getting red flagged on new residential installs), but it would be great to hear from some actual inspectors about their veiws on this.
Click to expand...


In the IRC, where stud cavities are used for return air, cables are allowed to be run perpendicular to the cavity. (meaning horizontal through the studs but not inside the cavity parallel to the studs):thumbsup::thumbsdown:
 
I saw the same episode and was curious as well. My only thought was it must have been listed and approved for the application in which case following the manufactures instructions would allow it. As stated its not the fist time equipment has been questionable in terms of the NEC.

That being said I don't think the plumber comment is fair. The guys on that show are true professionals in my opinion. It would frustrate me to read stereotypical comments about electricians.
 
Status
Not open for further replies.
Top