Washdown Rated Motors and Explosionproof Rated Motors

[mustang17]

I have a pumping application with three 5 HP motors on full voltage starters. Motors and pumps are floor mounted on housekeeping pads in a class 1, div 1 area. Motors are explosion proof.

Due to some problems in the process the floor has required frequent hosing and during a recent wash-down activity an operator with wet leather boots, and wet hands felt tingling coming up both legs from the floor. We checked for proper equipment grounding in the building and made sure all metal and plumbing including floor drains was at the same potential. This checked out good.

Even though the operator claims that he did not hit the motor directly with the stream of water coming out of the hose I have a difficult time understanding how they might have felt current. Explosion proof motors although not submergence proof are very tight. It would seem that you would have to stand there with the water directly on the motor for minutes and even perhaps hours to get water to leak into the motor and perhaps be able to pass current through your body to ground.

This also led me to question the application. We have no choice but to use explosion proof motors due to the hazardous area but I was not able to find an exp rated motor that was also wash-down rated. Anyone know if such a motor exists?


Finally I do not know all OSHA standard and who possibly could but does anyone know what would be a recommended operational practice with regards to wash-down activities using an exp motor. Should they be locking it out. What about with a wash-down rated motor. Would it then be acceptable to keep the wash-down rated motors running while wash-down activities proceeded?

Thanks, Ed

 

[controlsdude]

Electrical install has to be weatherproof for wash down and the conduit is RTRC (reinforced thermo resin conduit). If you dont meet this in that room then washdown would cause some issues like your describing.

If your room meets that then I would check for a broken or loose seal in your electrical install. Open up cabinets to inspect if any water has penetrated in any enclosures for a hint where it could be after washdown.

 

[Compositepro]

If all equipment is properly grounded I don't see how a shock is possible, event if the motor gets wet inside. The body can easily misinterpret nerve sensations as shocks. If there were a grounding problem it should be pretty easy to find.

 

[mustang17]

I have a theory as to what may be going on. Feel free to offer opposing or supporting viewpoints. I wrote and sent the statement below to the operator to help me understand their experience more. On a side note this person has had some issues with nerve damage so that theory is also very possible.

"For me it is conceivable that if any of these three recirculation pump motors had a small amount of water in them the day that you were doing the wash-down activities because they were partially submerged in sludge foam. It is also possible that some arching between the motor internals and the motor frame would have occurred but with arching there often is not enough of a sustained ground fault to trip a breaker. If this had happened the design of the system is such that the equipment grounding system would have drained this current to ground but the problem is you were wet, and your feet were wet and even though there is an equipment grounding system in place, you became a parallel conductor of a different, greater resistance, but still you are a parallel conductor and conductors in parallel of different resistances are current dividers. Whatever the total available ground fault current may have been most would have passed through the equipment ground due to its very low resistance, but your hose, hands, body and wet boots became the other conductor and this offered much higher resistance so the current again was probably into the level of micro amps due to your high resistance. Regardless, with the hose in your hands and if the spray inadvertently hit the pump motor during a ground fault you still could have passed some ground fault current through your body and wet boots to ground that could have came from one of those motors.