Explosion proof boxes and sealoffs

[KyleFowler]

So my co-workers are going to be hooking up a propane pump and since I'm the guy with a codebook they are asking me questions about the proper way to do it. So I've been reading Article 501 to learn. It seems like all the work they are doing is going to be in a Class 1 Div 1 area. My question is do explosion proof boxes typically need seal offs on the conduits coming into the box if the conduits are less than 2" in size and the box contains just wire nuts? I see seal offs are required if the box contains switches, outlets or other "ignition sources". Are wirenuts considered ignition sources? I know wire nuts aren't exactly ignition sources under normal circumstances but I think we have all seen our share of burned up wirenuts! Basically I'm asking to cover all the bases. An example of a box with just wirenuts would be the box at the motor.

Thanks in advance for probably a dumb question lol

PS-holy cow, explosion proof flexible couplings are expensive!

 

[kwired]

So my co-workers are going to be hooking up a propane pump and since I'm the guy with a codebook they are asking me questions about the proper way to do it. So I've been reading Article 501 to learn. It seems like all the work they are doing is going to be in a Class 1 Div 1 area. My question is do explosion proof boxes typically need seal offs on the conduits coming into the box if the conduits are less than 2" in size and the box contains just wire nuts? I see seal offs are required if the box contains switches, outlets or other "ignition sources". Are wirenuts considered ignition sources? I know wire nuts aren't exactly ignition sources under normal circumstances but I think we have all seen our share of burned up wirenuts! Basically I'm asking to cover all the bases. An example of a box with just wirenuts would be the box at the motor.

Thanks in advance for probably a dumb question lol

PS-holy cow, explosion proof flexible couplings are expensive!

No, under normal operating conditions a wire nut doesn't produce arcs like a switch contact opening/closing does.

Some of the concepts involved here is you are not very easily going to make something that keeps vapors out, but rather are designing it to be able to contain an explosion when one happens. By having the seal close to the enclosure containing the parts that are an ignition source you effectively reduce the size of that enclosure instead of allowing the pressure from the explosion to run throughout the entire piping system.

Hot gases from the explosion have to pass through voids in threaded entries to reach exterior and ignite any vapors outside the enclosed system. By the time they pass through those threads and/or other mating surfaces designed for these kinds of locations those gases have cooled to a safe temp for the hazardous location on the outside.

 

[oldsparky52]

PS-holy cow, explosion proof flexible couplings are expensive!

That is a bit of an understatement.