Disconnecting means for medium voltage motors

[weressl]

given the opportunity, I will. I was in hopes that your knowledge and experience might shed some light on the FPN.

My only experience is that I have never seen a MV motor equipped with an additional 'local' disconnect in addition to the remote controller. I really would like to see one and if ANYONE has a picture of such, please post it. (No Photoshop please.) In this particular case a local disconnect in a treatment plant would represent additional hazard to both operators and equipment. MV equipment belonngs indoors and when outside it shoul be kept away from chemicals and other environmental factors that may cause harm and malfunction.

I agree that facility operation is well outside my realm, but compliance with the NEC is not. Exception (b) sets forth some stipulations beyond the location being "industrial". If one wishes to take advantage of a Code "exception", I feel it is their obligation to show they meet the criteria set forth in the exception. Other than being a "treatment plant" I did not notice if the OP mentioned "municipal" or not and I have no idea what Subpart regulations they might be required to operate under. That is where I was leading with my comment. IMHO, some documentation would be in order before an inspector should sign off on any exception.

Couple of things here.

IMO the Code is written, but if an AHJ tries to 'enforce' certain parts of it they will find themselves in contradiction with other civic laws which are applicable. In other words it's a catch 22.

The other issue is practical. There is no way that an MV gear can be operated by ANYBODY but a qualified person as defined by OSHA.

The inspector is authorized to inspect plans and physical facilities and that is where their authority ends. They have to make their judgment based on that.

Unfortunately all these entities - Federal, State, Local authorities and Engineers/Architects, Installers and Inspectors are all operate within their 'silos' without really understanding in detail the impact of their work and requirement on the others.

 

[jdsmith]

...In this particular case a local disconnect in a treatment plant would represent additional hazard to both operators and equipment. MV equipment belongs indoors and when outside it should be kept away from chemicals and other environmental factors that may cause harm and malfunction.

I agree that medium voltage (air or vacuum) equipment belongs in a climate controlled, humidity controlled environment. Any such MV equipment installed in a pumphouse or process area would present an increased hazard to any personnel in the area due to the increased deterioration rate of the equipment from the atmospheric conditions and the chance of fluids entering the enclosure. I would argue that NEMA 3R medium voltage equipment is in the same category and should not be used at all.

We have a firewater pumphouse located on the edge of a pond and we have 4160V motor starters, a 480V switchboard, and a 480V starter in the same room with two 400HP motors and a 150HP motor, all on vertical pumps. The pump outlets, instrumentation, gate valves, and control valves are all in the same room with the electrical equipment. We have had incidents in the past where piping has leaked vigorously and sprayed water on the 4160V and 480V equipment - fortunately nothing happened, but we built a sheet metal wall in between and added a firewater pumphouse substation to our electrical reliability long range plan.

I don't know why the CMP chose to write 100HP in the FPN, but I would certainly think MV equipment would qualify.