I have an old gas make-up blower unit on the roof of my facility and noticed the previously installed MC cable sheathing for motor line and load has deteriorated. I am looking into replacing the conduit And was wondering if the NEC specifies such a scenario as requiring a flame retardant or flame resistant conduit. The reason being, is that the electrical conductors referenced is run inside the cabinet of unit only a few feet away from an open flame.
Flame retardant conduit or no?
- Thread starter Wcrook581
- Start date
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I would not use non-metallic conduit if that's what you're asking.
How was the MC cable deteriorating? Was it exposed to the exterior on the roof? I've installed make-up air (MUA) units and they typically have a factory-wired power drop consisting of conductors sheathed in aluminum flex conduit (similar to MC). But those drops are intended to be fed through the roof within the MUA's equipment curb so they are not exposed to the weather.
Typical MC cable is not rated for exposure in wet locations; you must use MC cable specifically listed for wet locations. But I would not install MC cable of any kind exposed on the roof because it would be subject to damage from anyone walking/working on the roof.
IMO, EMT is the minimum that should be installed on roof tops. But for flat commercial roofs, I only use rigid conduit for exposed work on the roof. I've seen too many damaged EMT conduits from workers stepping on them, tripping on them, lifting equipment over them, etc.
How was the MC cable deteriorating? Was it exposed to the exterior on the roof? I've installed make-up air (MUA) units and they typically have a factory-wired power drop consisting of conductors sheathed in aluminum flex conduit (similar to MC). But those drops are intended to be fed through the roof within the MUA's equipment curb so they are not exposed to the weather.
Typical MC cable is not rated for exposure in wet locations; you must use MC cable specifically listed for wet locations. But I would not install MC cable of any kind exposed on the roof because it would be subject to damage from anyone walking/working on the roof.
IMO, EMT is the minimum that should be installed on roof tops. But for flat commercial roofs, I only use rigid conduit for exposed work on the roof. I've seen too many damaged EMT conduits from workers stepping on them, tripping on them, lifting equipment over them, etc.
hbiss
EC, New York NEC: 2017
- Location
- Little Falls, New York NEC: 2017
- Occupation
- EC
No idea what it looks like. The NEC has nothing to say about internal wiring either. But from what I think you are saying, the cable (how do you know it's MC?) is inside the unit. Commonly it is FMC or Greenfield with THHN or MTW conductors run through it. You could replace it with aluminum FMC to minimize any corrosion. I don't think that being a few feet away from the burners would cause it to be hot enough to be concerned about unless you actually determined that it was overheating. In that case there are high temperature conductors that you can use.
-Hal
hbiss
EC, New York NEC: 2017
- Location
- Little Falls, New York NEC: 2017
- Occupation
- EC
Perhaps there used to be a divider or compartment that is no longer there. Could be also that this is something done by a service tech, not original.
-Hal
Eddie702
Licensed Electrician
- Location
- Western Massachusetts
- Occupation
- Electrician
MUA air units have no heat exchanger you bring in outdoor air and the burners fire and heat the air directly....direct fired unit the heated air is ducted into the building You have cold outside air at the intake to the unit. As long as the wires are not near the flame you should be fine. Discharge temps on the air is seldom over 110-120
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