I'm hooking-up blowers in some paint booths. These are unsealed, relatively thin steel boxes with bolted together sides. There is a 1/2 hp, 120V, thermally protected motor in each of the four units (per booth). The installation instructions call for the sides/covers to be caulked as they are assembled.
I have two questions. First of all, how can these blower motors be installed in a hazardous location. The construction of the blower box is essentially like using a standard 8x8 steel junction box to house a potential spark producing device inside a hazardous location. Even if I caulked the cover shut, I couldn't get away with such an installation. Also, the multiple caulked covers that would need to be removed to access the motors for service does not seem right to me.
My second question concerns the pipe I need to use to feed these units. The blower housings are not made to have a pipe mounted to them. Instead, 2" holes are provided in the backs to run a flexible pipe through and to the motor. I am going to run a pipe down from the booth ceiling and into the top of the boxes. Six inches of this pipe will be exposed inside the paint booth. There will not be any exposed connectors or couplings and the pipe will be caulked where it enters the booth and where it goes through the caulked-on thin steel top of the blower housing. Once inside, the conduit will be converted to flex and run into the motor.
I am assuming that no disconnect will be needed at the motor since it is inside a hazardous location. However, does the exposed, short, unspliced conduit I use have to be rigid inside the booth and sealed off as soon as it passes through the booth ceiling. Normally, I would be very confident that it would but the apparently "legal" -but flimsy- construction of the blower boxes have me confused.
I guess I should have mentioned that these blowers are designed for paint booths and have some sort of listing for that purpose. I can only imagine that either somebody got paid off big time to allow such a thing or that I completely misunderstand this type of hazardous location. Even though I would normally never imagine doing such a thing, my plan is to use no seal-offs or rigid pipe. It makes no sence what-so-ever with the half-azz box I am running to.
The crux of any classified location is the actual classification of the specific area, and its' boundaries.
Most paint booths are designed to -technically, at least- place the lights and fans outside of the classified zone.
Keep in mind the very big difference in classification of the zone, between "always exposed to hazardous atmospheres" and "only exposed if something breaks." In most instances,TEFC motors, with the starters mounted well away, meet the qualifications. Nor do junction boxes, etc., need to be rated 'explosion proof' if they are in a 'zone 2', are gasketed, and contain no sparking contacts. (Keep THAT detail in mind when mounting your disconnects!)
Oddly enough, your greatest concern is in the grounding of the fans; moving air can create static electricity.