300.22 (B) or (C) Which one is applicable?

[W@ttson]

Hello,

Here is the environment:

I have a very very large room. It is 67'x95'. This room houses very large blowers which blow air into this large open room and pressurize the room. The high pressure air is diverted into a system to supply fresh air to a later portion of the facility. This is a "plenum chamber". The room has the motors etc for the blowers within it. It also has MCCs to operate the motors. All of this seems fine to since it is as per 300.22(B) so far.

The question is, is this really a plenum specifically constructed for air handling? Or is it "other spaces used for environmental air? I would like to use some of the space to install a transformer and want to see if I am actually required to enclose it within this large open space or if it will be complaint since it falls under 300.22(C).

 

[Dennis Alwon]

IMO, that is no different than having equipment in a hung ceiling where the space is used as a cold air return. It definitely falls under (C)

 

[W@ttson]

IMO, that is no different than having equipment in a hung ceiling where the space is used as a cold air return. It definitely falls under (C)

Yes, that was my first thought. However, the transformer I want to install is much much larger than 50KVA (it's 225kva). How does that change things? I have plenty of space, and access would even be "ready". I would imagine that it still falls under (C)?

 

[GoldDigger]

I would be inclined to consider the room to be a plenum. In particular it is enclosing pressurized supply air going to occupied parts of the building. And, other than housing the motors and their controls it has no other uses.

A dropped ceiling has a number of uses, in terms of sound control, light mounting, concealing infrastructure located above it, etc. The air handling really is, to that extent incidental.

In the OP's case the primary purpose of the room may be taken as air handling, and just a blowers could be housed within a single purpose duct, the blowers in this room are incidental. On the other hand, if the room is to be considered a plenum, it is not clear that it is legal to have the MCCs there too.

 

[Dennis Alwon]

I know of no code rule that talks about the size of a trany in an air space. Maybe someone knows something

 

[GoldDigger]

I know of no code rule that talks about the size of a trany in an air space. Maybe someone knows something

I think that the code the OP is referring to is the one which governs putting a transformer above a suspended ceiling, whether that area is a plenum or environmental air space or neither.

 

[W@ttson]

I think that the code the OP is referring to is the one which governs putting a transformer above a suspended ceiling, whether that area is a plenum or environmental air space or neither.

Yes, I guess I was referring to 450.13?? I started thinking that same way GoldDigger regarding its sole purpose. But then, agin it's not something constructed. For example, I can construct a drywall box to be a plenum for the specific use of air handling. But can I construct a room?

 

[GoldDigger]

Yes, I guess I was referring to 450.13?? I started thinking that same way GoldDigger regarding its sole purpose. But then, agin it's not something constructed. For example, I can construct a drywall box to be a plenum for the specific use of air handling. But can I construct a room?

Just how do you think that the room came into being if it was not constructed?
The whole building was probably constructed at the same time.
They call it the construction industry.
Were you thinking fabricated instead? That is not the code language, I think.

 

[W@ttson]

Just how do you think that the room came into being if it was not constructed?
The whole building was probably constructed at the same time.
They call it the construction industry.
Were you thinking fabricated instead? That is not the code language, I think.

I guess what what I meant is that in the case of a metal duct or tin or drywall duct specifically constructed for environmental air movement, I would not be able to walk in it. In the hollow space above a ceiling I would be able to walk in it. I guess to get to the bottom of this, I think it needs to be found out what the intent is to have a difference between 300.22(B) and (C). What is the intent of allowing more items in environmental air spaces versus a metal duct?

 

[W@ttson]

Actually, I think I just confirmed that it is a 300.22(C). 300.22(B) Reads as follows:

2017 NEC:

(B) Ducts Specifically Fabricated for Environmental Air.
Equipment, devices, and the wiring methods specified in this section 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 luminaries shall be permitted.

Only wiring methods consisting of Type MI cable without an overall nonmetallic covering, Type MC cable employing a smooth or corrugated impervious metal sheath without an overall nonmetallic covering, electrical metallic tubing, flexible metallic tubing, intermediate meal 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 (4ft), 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.

The section actually does specify the duct as fabricated. Now what is the definition of fabricated??? :?

Since I think you can only fabricated a metal/fiberglass/tin/drywall etc duct and you can not fabricate a room, then 300.22(B) is not applicable for this situation and 300.22(C) is what should be referred to.

I guess what what I meant is that in the case of a metal duct or tin or drywall duct specifically constructed for environmental air movement, I would not be able to walk in it. In the hollow space above a ceiling I would be able to walk in it. I guess to get to the bottom of this, I think it needs to be found out what the intent is to have a difference between 300.22(B) and (C). What is the intent of allowing more items in environmental air spaces versus a metal duct?