Plenum rated power cabling (?)

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Schmoleskin

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Denver, CO, USA
​Greetings, we are building a project that supplies combustion air to a standby generator. It contains air filters, a water droplet removal system, silencing baffles and 12 three-phase motors to provide forced-air for higher air volume.

The motors are European made, so come with metric cable glands for power and control interface (yes, controls, each motor has its own on-board VFD). Does anyone know of a type of cable that could be used for powering these motors that is also plenum-rated? The motor FLA is only 9A, so a 4/Conductor #14 would be enough to provide three phases and a ground.

Omni cable makes a 4/C #14 plenum cable, but it is CL3P, and only rated 300V, not good enough to supply these 480V motors. I looked into MI cable, but the termination process seems a bit too time-consuming, and is incompatible with the existing cable glands.

Does anyone know of another option here in plenum-rated cable (or other slick wiring method) that could just terminate in cable glands? Or will we end up removing them and using a plenum approved wiring method like un-coated steel flex?
 
Where is the plenum? The generator room itself, or any ductwork supplying fresh air from the outside, do not fit the NEC definition of a plenum, which is used for environmental air.

If the wiring supplying the motors actually has to go through a space for environmental air, see 300.22(B). Wiring within one of the raceways can be standard conductors, they do not have to be plenum rated.
 
Needed to describe it better, the air intake structure sits above the generator room, and supplies air to the room, in which the generator resides. I feel like that is environmental air, since if you are in the gen room, your breathing air is coming through the intake structure. The fans are right in the air stream entering the gen room. You can stand up and walk around in the intake air structure, it is a big genset.

I read your code article, and agree that the conductors within raceways can be standard material. I was just trying to find an easy way to wire them without having to swap out the cable glands for flex connectors and run all the flex. I have checked with a few suppliers, and none have come up with a plenum rated 600V cable. I think we are going to just run all the flex and use regular conductors. Thank you.
 
Schmoleskin said:
Needed to describe it better, the air intake structure sits above the generator room, and supplies air to the room, in which the generator resides. I feel like that is environmental air, since if you are in the gen room, your breathing air is coming through the intake structure. The fans are right in the air stream entering the gen room. You can stand up and walk around in the intake air structure, it is a big genset.

I read your code article, and agree that the conductors within raceways can be standard material. I was just trying to find an easy way to wire them without having to swap out the cable glands for flex connectors and run all the flex. I have checked with a few suppliers, and none have come up with a plenum rated 600V cable. I think we are going to just run all the flex and use regular conductors. Thank you.
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Under 300.22(C) it states that it "does not include habitable rooms OR areas of buildings, the prime purpose of which is not air handling". The prime purpose of the generator room is to handle air for the generator, not for environmental air, ie for people.

The purpose of this code section is to not allow flammable materials that emit toxic smoke into an area that would be recirculated into other parts of the building, killing everyone with toxic smoke. For an example of this, see the 1980 MGM Grand Hotel fire in Las Vegas

As I see the code section, your generator room is not an air handling space in the sense of the NEC.
 
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To give another example, most residential attics are ventilated through a ridge vent, soffits, and convection. While air does indeed move in the space, it is not an air handling space per se, and one does not have to use plenum rated cable in an attic... The air is not used for environmental air.
 
While I agree with your statement above that the generator room is to handle air for the generator, I think the intake structure I have described is a plenum, because of the below underlined portions of 300.22(C):

(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.

The air intake structure however, is specifically fabricated for environmental air-handling purposes, but as you said, the generator room itself is not. To be safe, we have decided to use un-coated flex with regular conductors for power wiring per this:

...Other types of
cables, conductors, and raceways shall be permitted to be
installed in electrical metallic tubing, flexible metallic tubing,
intermediate metal conduit, rigid metal conduit without an
overall nonmetallic covering, flexible metal conduit...

The low voltage control wiring can easily be done with plenum-rated cable. Thank you again for your help.
 
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