Control cabinet in C1D2 area

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AJElectric

Member
Location
Iowa
We're being asked to build a PLC control cabinet with contactors, etc. for motor loads for to be installed in a C1D2 area; also other various circuit boards and controllers besides the PLC. The cabinet will be air-conditioned using an AC unit labeled for C1D2. It will be a NEMA-4 enclosure pressurized & purged as per 501.105(A), following NFPA 496 standards for this.

One possible technicality - wording in the code I don't fully understand is 501.120(B)(3) - there are resistors in the PLC and any other printed circuit boards in the control cabinet. So my first question is does this rule out any circuit boards that aren't listed for C1 areas? Which pretty much rules out the control cabinet being in this area? I'm guessing there are other technicalities besides 501.120(B)(3) that I'm not seeing?

My second question - It seems that technically this whole idea of having a purged NEMA-4 control cabinet in the C1D2 area is permissible, but I'm wondering whether it will actually pass with the AHJ? Is there a precedence for this sort of thing being done as long as it's a purged cabinet according to NFPA 496?

Following that, I'm also wondering how to actually comply with the NFPA 496 "Type Z Pressurizing" which will be required. Can this simply be done with a compressed air feed, differential pressure sensor, and connected alarm/buzzer? It's easy for us to build since we do a lot of instrumentation/integration work, again I'm apprehensive that it would pass with the AHJ and I don't know what the expectation really is here.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Keep in mind you are effectively creating a non-classified space inside the enclosure.

Pressurized/purged cabinets are pretty common. Some places pressurize whole rooms. I doubt you will have any problem getting it past an AHJ. It would probably be best if the control panel was UL listed to UL 508a.

The purge/pressurization system would be best purchased from a company that makes them listed to the appropriate UL standard. Pepperl and Fuchs bought Bebco. When I was doing purged systems I always used Bebco. I think Hoffman sells them too, and maybe Phoenix.
 
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retirede

Senior Member
Location
Illinois
The purge/pressurization system would be best purchased from a company that makes them listed to the appropriate UL standard. Pepperl and Fuchs bought Bebco. When I was doing purged systems I always used Bebco. I think Hoffman sells them too, and maybe Phoenix.

I second this! Do not roll your own…
 

AJElectric

Member
Location
Iowa
Thanks for the tips guys. I see your point that even if it technically meets code, doesn't mean an inspector will pass it. This is a somewhat unique situation so we'll have to feel it out with the client and see what they really want.

The A/C unit will be Bebco, but our Bebco vendor recommended this brand of purge unit:
 
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