Bob,
Please don't take this wrong, I respect you and your opinions here. It's just that this is a personal pet peeve of mine that I had to get into in more depth than I cared for once as a product manager responsible for UL listings of my assigned product group. Our products needed ventilation, I could not sign my name to the UL reports that said they were Type 1 and then allow Marketing to sell it as Type 12. The subject was a constant source of contentious discussion between my company president, the marketing department and me, as the only one of the bunch who applied Engineering principals to the discussion. I ultimately lost the battle, but only because the president resorted to "because I said so". So please take all that into consideration as to why I happen to be a little obsessive-compulsive over this issue. I'm not really opposing your point of view so much as spreading the truth as I see it.
there are now fans and grills that are UL listed as type 12 so it is indeed possible to ventilate a type 12 cabinet.
I don't disagree that people are
selling this, and what you believe is exactly what they WANT you to believe. But that doesn't make it true. UL50, the standard for enclosures that dictates the environmental test requirements, makes no allowances that a filtered vent fan would squeeze in under. Vent fans in fact are not even mentioned in UL50 specs. So what these companies are doing is a little bit of slight-of-hand. If you look, companies like Hoffman that have a reputation to maintain, do NOT ever say that filtered vent fans are Type 12, NEMA or UL. Those that DO say it are those who appear to be trying to capitalize on Hoffman's reluctance to join the party, because by saying it (implying it really), they can attract people who want to believe it.
- The fan is UL listed under UL508A, which does NOT address enclosure ratings. But still, it's a "true" statement that it is UL listed.
- They tell you the fan is "NEMA 12", hoping you will not realize that NEMA is not a testing or listing agency, so you can say anything you like that is preceded by NEMA, there is nobody to answer to on it but your own conscience. It's less clear cut, but not blatantly false.
- Then some go so far as to say this: "Maintains a UL Tested NEMA Type 12 seal against enclosure". That means that they put a gasket around the base of the fan, then test the gasket seal against UL50 test standards. But there is NO WAY the big gaping opening on that fan itself will stop atomized water and cement dust, the test criteria for Type 12. But they didn't technically say that, they said only that the GASKET was tested. Again, not technically a lie.
UL50 Type 12 says that the acceptable level of dust or atomized water entry is ZERO. In the UL50 dust test, the Portland cement dust they use is required to have a particle mixture with no less 82% of the particles being 0.0015" in diameter (about 38 microns). Most of the filtered "NEMA 12 Fan Kits" use a filter that is at best, "G3" rated, which is essentially meant to exclude up to 80% of "coarse" airborne particles that are a mixture of "Arizona road dust, carbon black and cotton lint", but no specific size. 20% can get through, and 20% is greater than zero.