raised floor in semi conductor fab cleanroom

[caporter]

Am I being overly restrictive and costing the company more money than necessary?

Our cleanroom floors are used for return air and running various utilities to the manufacturing tools. As such I believe they fall into the "other space used for environmental air" described in NEC 2008 300.22(C) and do not meet the requirements for section 645.4 in any way.

My clients (process engineers) are wanting to install Varian scroll pumps, place outlets, and run power cords (SO) for the tools under the floor. There is also extensive use of liquid tight flexible metal conduit with the standard PVC jacket under the floor. I believe these are all in violation of current code but may have been allowed under older versions.

I am requiring the LFMC (sealtite) to be low smoke halogen free (listed for restricted or self contained ventilation areas) and rejecting requests to place electrical devices, power cords and all under the floor.

Does this all sound right or am I over looking exceptions that might save time & money while being safe?

 

[EEJaime]

Anything installed in the air stream must be specifically listed and approved for that application. Nothing that does not meet the flame retardent, flame spread requirements of applicable codes cannot be in there.

You need to get the rest of the team on your page. You are not being overly restrictive, if anything happens and you pump a building full of PVC products of combustion, I don't think that they will say, "well, he told us not to but we did it anyway". They are going to say, "NOBODY told us that!"

And you are under 300-22(B), because this IS an air plenum. Note especially the provision that states: "Equipment and devices shall be permitted within such ducts or plenums ONLY if necessary for their direct action upon, or sensing of the contained air". In other words, you can't locate ANY equipment in the plenum that is not for the control of sensing or the air.

Good luck,
EEJaime

 

[caporter]

The raised floor in the cleanroom is only an air plenum as much as the area above a suspended ceiling used for return air is an air plenum. The NEC handbook specifically uses a return air plenum above the ceiling as an example.

 

[caporter]

Sorry didn't complete the reply.

(C) Other Space Used for Environmental Air. This section applies to space used for environmental air-handling purposes other than ducts and plenums as specified in 300.22(A) and (B). It does not include habitable rooms or areas of buildings, the prime purpose of which is not air handling.


Section 300.22(C) applies to other spaces that are used to transport environmental air and that are not specifically manufactured as ducts or plenums, such as the space or cavity between a structural floor or roof and a suspended (hung) ceiling. Many spaces above suspended ceilings are intended to transport return air. Some spaces are also used for supply air, but they are far less common than those used for return air. This section does not apply to habitable rooms and other areas whose prime purpose is other than air handling. Such an area is shown in Exhibit 300.19. If the prime purpose of the room or space is air handling as depicted in Exhibit 300.19, the restrictions in 300.22(C) apply, whether or not electrical equipment is located in the room.

 

[RonShap]

I agree that you are dealing with an Other Space Used for Environmental Air. Raceway cannot have an overall nonmetalic jacket per 300.22(C)(1). You cannot use cords below the floor due to 400.8.
You are right.

 

[alehman]

Plenum-rated LFMC is available. I don't know if it would be considered acceptable per 300.22(C).

Alan
“The engineer's first problem in any design situation is to discover what the problem really is.” Unk.