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In our previous installment, we pointed out that where you locate a motor matters. We looked at the two basic requirements [430.14] of ventilation and maintenance access. These apply to all motors.
But if your motor is located where flying dust or fibers might accumulate on it, another requirement applies. Before we get to what that requirement is, we need to be clear that you do not need ignitable dust (Class II, Article 502) or ignitable fibers (Class III, Article 503) for this requirement to apply. It’s not about igniting the dust or fibers; it’s about suffocating the motor under the accumulation.
The requirement is that you use a suitable type of enclosed motor that won’t overheat under the prevailing conditions [430.16]. This requirement is followed by an informational note that says you may have to use enclosed-pipe ventilated motors or an enclosure in a separate dust-tight room (properly ventilated) if the situation is bad enough.
What’s not explicitly stated in this requirement is that you have the option of altering the prevailing conditions rather than just adapting to them. A hint toward that end is in the informational note.
One way this is done is to build a small sheet metal structure similar to an air handling duct around the motor, then duct in forced air to provide a positive pressure within that structure. All such structures have the same size intake fan supply opening with an easy-change filter secured by hook and loop fastener.