Air Plenums and Electrical Equipment

[Artemis]

An existing building has an air plenum that has distribution panelboards, dry type transformers and disconnects located in them. I am aware of section 300.22 for wiring requirements, what sections or other codes correlate to electrical equipment located in these plenums.

 

[wbalsam1]

Hi: In NYS we refer to the Mechanical Code and more specifically to Chapter 6 on Duct systems at Section 602 on Plenums. 602.2.1.1 establishes a peak optical density not greater than 0.50, an average not greater than 0.15 and a flamespread not greater than 5 feet. 602.2.1.4 refers to combustible electrical equipment not having a greater peak rate of heat release than 100 kilowatts, peak optical density not greater than 0.50 and average not greater than 0.15. See UL 2043 & UL 910, also.

 

[iwire]

I am aware of section 300.22 for wiring requirements, what sections or other codes correlate to electrical equipment located in these plenums.

300.22 pertains to the equipment as well as the 'wiring requirements'.

Are we really talking about a plenum {300.22(A) 300.22(B)} or our we taking about 'other spaces used for Environmental air'? {300.22(C)}

If it is a plenum (duct) the NEC pretty much prohibits all electrical equipment.

If its 'other space' (like above a suspended ceiling used for return air) then some equipment can be located in it.

Can you describe what you have a bit more?

 

[wbalsam1]

Artemus

Artemus

Is the mechanical / electrical room(s) a part of the air plenum?

 

[Artemis]

It is a vertical air plenum used for HVAC system with open grate floors.

 

[iwire]

It sounds to me like that is a duct covered by 300.22(B).

If so the last 1/3 of that section pretty much rules out all electrical equipment or devices that do not either act upon or sense the air.

Panels are certainly not allowed in a duct.

 

[steve66]

I am still kind of doubting that this is a plenum per the NEC definition. In particular, was it "specifically fabricated to transport enviromental air"? Or is it more like a room that the HVAC equipment is located in?

The Handbook has a diagram of a room being used to transport air. The room has both an airhandler and a panelboard shown in it.

If the space is an "other space used for enviromental air", 300.22(C)(2) allows electrical equipment with a metal enclosure (even if the enclosure is ventilated, like a transformer.)

Steve

 

[iwire]

I am still kind of doubting that this is a plenum per the NEC definition. In particular, was it "specifically fabricated to transport environmental air"? Or is it more like a room that the HVAC equipment is located in?

I agree Steve, it could go either way.

However in a lot of taller buildings there are literally rooms expressly fabricated for the transport of environmental air.

The fact it has open grate floors suggests to me this room is located on the top of return air chases in a taller building.

Of course I may be well off the mark.

 

[Mike01]

simmilar dilema

simmilar dilema

I have a simmilar dilema and trying to research it right now and would like to hear everyones opinion:

I hav an enclosed space that includes two large air handlers in a arena the two air handlers bolth supply air from this space and there is a opening in the floor (grated) for return air. There is room for electrical distribution within the space but is it aginst code...I will let you know what I find out I have a meeting with the local inspector to go over this.

 

[Artemis]

Thanks for all the great feedback! My assumption would be that this area would fall under 300.22 C. Since it is an ideal location to locate additional panels, would this come down to an interpretation from the AHJ?