Plenum Room Hazards

[jhpalkens]

I have a room in which there is a large fan, 40 hp, drawing from the room and discharging into supply ductwork for a rifle range.
the room has a connection to the outside air but is under a large negative pressure. In the room are other pieces of equipment, cord connected air compressors and pumps with open frame motors, circuit breaker panels and non-plenum rated wiring.
Are these conditions violating NFPA guidelines?

 

[Dennis Alwon]

I am sure some see it that way but think about a cold air return in a house. Is the whole house a plenum? I don't think so.

 

[hbiss]

I've seen that several times too. One time it was even hard to open the door from the outside. It opened out and the room was under negative pressure. The room would be considered an air handling space not a plenum.

-Hal

 

[don_resqcapt19]

It appears to me that the electrical system would have to comply with 300.22(C).

 

[jusme123]

It appears to me that the electrical system would have to comply with 300.22(C).

Part of 300.22(B) states; "Equipment and devices shall be permitted within such ducts or plenum chambers only if necessary for their direct action upon, or sensing of the contained air."

 

[don_resqcapt19]

Part of 300.22(B) states; "Equipment and devices shall be permitted within such ducts or plenum chambers only if necessary for their direct action upon, or sensing of the contained air."

I don't see the space in question as being covered by 300.22(B). In my opinion it is a 300.22(C) space.

 

[jusme123]

I don't see the space in question as being covered by 300.22(B). In my opinion it is a 300.22(C) space.

I believe it to be a plenum chamber, it basically has intake and output ducts.

 

[don_resqcapt19]

I believe it to be a plenum chamber, it basically has intake and output ducts.

In the 2011 code the rule only applies to "ducts" the words "plenum" and "plenum chamber" are not in the 2011 version of 300.22(B).

(B) Ducts Specifically Fabricated for Environmental Air. Only wiring methods consisting of Type MI cable, Type MC cable employing a smooth or corrugated impervious metal sheath without an overall nonmetallic covering, electrical metallic tubing, flexible metallic tubing, intermediate metal conduit, or rigid metal conduit without an overall nonmetallic covering shall be installed in ducts specifically fabricated to transport environmental air. Flexible metal conduit shall be permitted, in lengths not to exceed 1.2 m (4 ft), to connect physically adjustable equipment and devices permitted to be in these fabricated ducts. The connectors used with flexible metal conduit shall effectively close any openings in the connection. Equipment and devices shall be permitted within such ducts only if necessary for the direct action upon, or sensing of, the contained air. Where equipment or devices are installed and illumination is necessary to facilitate maintenance and repair, enclosed gasketed-type luminaires shall be permitted.

 

[jusme123]

In the 2011 code the rule only applies to "ducts" the words "plenum" and "plenum chamber" are not in the 2011 version of 300.22(B).

I dont own a 2011 code book, but thanks Don, now I better understand where your coming from.

 

[don_resqcapt19]

I dont own a 2011 code book, but thanks Don, now I better understand where your coming from.

Even under the 2008 code wording, I would still call it a 300.22(C) location. I don't see a room with equipment in it as a plenum chamber.

 

[the blur]

We do alot of plenum work above dropped ceilings. Some towns require plenum rated cable, some don't. either way I get under cut by contractors not quoting the job with plenum rated cable.

 

[don_resqcapt19]

We do alot of plenum work above dropped ceilings. Some towns require plenum rated cable, some don't. either way I get under cut by contractors not quoting the job with plenum rated cable.

If the space above the ceiling is used for the return air, then it is a 300.22(C) space and requires the use of plenum rated cable.