Explosion Proof Motors
November 23, 2013
Separating aqueous alcohol from food fiber and polymer is a major market for Vincent screw presses. These presses all use explosion-proof motors.
It seems all the explosion proof NEMA motors we have routinely purchased for decades are rated Class I, Division I, Group D and Class II, Group EFG; all of which are temperature rated T3B.
Class I covers us for the explosive gas environment, as opposed to Class II, which is dust.
Group D covers us for ethanol and the other solvents we see in our screw presses.
Division I covers us for being in an explosive atmosphere at least part of the time. That is a conservative step up from Division II.
We have asked our suppliers for a motor which goes beyond this. The specific we requested is if explosive vapors get drawn inside a motor, and these gasses eventually explode, is the motor built with flash propagation suppression such that an internal explosion will not set off a fire in an explosive atmosphere surrounding the outside of the motor?
This severe specification has arisen with European jobs which must meet ATEX (explosive atmosphere) standards.
ATEX separates applications by Zones. It says that in Zone 0, no motors are allowed. In Zone 1, an internal explosion inside a motor located in an explosive atmosphere will not set of an explosion in the surrounding atmosphere. Zone 2 is where the motor will not get hot enough (or spark) to set off a fire in an explosive surrounding atmosphere. Normally Zone 2 is specified.
The answer we have been given in regards to NEMA explosion proof motors is that this "Zone 1" requirement is something that must be quoted by the factory, and many factories making explosion proof motors do not offer this option. No one has been able to detail it in terms of Class, Division, Group, or Temperature Rating.
Incidentally, the price of the ATEX motors about doubles when the specification goes from Zone 2 to Zone 1.