purged and pressurized enclosures - how to make or buy

[megloff11x]

I'd asked before and the replies indicated that one should start with a NEMA 4 box, blow air through it, and add a listed differential pressure switch, wiring the alarm per NFPA 496.

Has anything changed with the 2005 code?

Does anyone sell a listed enclosure (or line of them) specifically for purged and pressurized applications?

Matt

 

[rbalex]

Re: purged and pressurized enclosures - how to make or buy

...
Has anything changed with the 2005 code?
...

The definition has changed a bit but the advice is the same.

 

[petersonra]

Re: purged and pressurized enclosures - how to make or buy

I'd asked before and the replies indicated that one should start with a NEMA 4 box, blow air through it, and add a listed differential pressure switch, wiring the alarm per NFPA 496.

Has anything changed with the 2005 code?

Does anyone sell a listed enclosure (or line of them) specifically for purged and pressurized applications?

Matt

There is no reason to have an enclosure listed for this purpose since there is no requirement that the enclosure be anything other than gasketed.

I use prebuilt assemblies rather than DIY style. Bebco (now P&F I think) and Hoffman sell kits to do this with pretty decent support for determining just what is needed, have a UL listing on the assembly, and even make nameplates with the right wording. Much easier than trying to come up with all the stuff yourself for an occasional pressurized enclosure.

 

[rbalex]

Re: purged and pressurized enclosures - how to make or buy

...

There is no reason to have an enclosure listed for this purpose since there is no requirement that the enclosure be anything other than gasketed.

...

Gaskets aren't necessarily required either. Any enclosure that would otherwise be appropriate for the ordinary location may be purged or pressurized per NFPA 496.

"Purged and Pressurized" is a protection technique recognized under 500.7(D). Under the main rule of 500.7 it "... shall be acceptable..." Neither the root definition in 500.2, the protection description in 500.7, nor the installation standard in 496 require gasketing. This isn't to say its a bad idea, of course.

 

[petersonra]

Re: purged and pressurized enclosures - how to make or buy

...

There is no reason to have an enclosure listed for this purpose since there is no requirement that the enclosure be anything other than gasketed.

...

Gaskets aren't necessarily required either. Any enclosure that would otherwise be appropriate for the ordinary location may be purged or pressurized per NFPA 496.

"Purged and Pressurized" is a protection technique recognized under 500.7(D). Under the main rule of 500.7 it "... shall be acceptable..." Neither the root definition in 500.2, the protection description in 500.7, nor the installation standard in 496 require gasketing. This isn't to say its a bad idea, of course.

You are absolutely right.

I looked in the Hoffman catalog and it indicates the enclosure should be metal and rated NEMA 12, 4, or 4X. Bebco's literature also indicates they must be used on type 4 or 12 enclosures. Maybe the listing on these assemblies requires it, but the standard does not.

I wonder how one would ever get an ungasketed enclosure to pressurize? Its hard enough with a gasketed one. Lots of air I guess.