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Requirement for Remote Control Unit (RCU) for small motor

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ppmsb

Mechanical
Jul 6, 2007
29
Hi,

Our company standard states the following requirements:

"Electric drives shall be provided with an RCU mounted local to the motor. By means of this RCU, motors can be started/stopped and, in the "O" (neutral) position, automatically control"

Is this common practice even for small LV motor (< 50kW)?

ppm
 
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That sounds like the "Hand-Off-Automatic" switch that was almost universal for air handling motors in commercial installations when I was working in that field. I haven't done much of that type of work for a few decades so I don't know what is current know.
respectfully
 
Yes, fairly commonplace, as ON-OFF-AUTO (or HAND-off-auto) switches. Less common in highly interlocked systems, but I've even worked with them there. Horsepower, or perhaps more accurately motor size, is of no consideration.

Please let us all know how this works out for you! and don't forget faq731-376
 
It is an issue for us becoz our company standard requires RCU but the OEM for our gas turbine package states that it is not their standard practice to supply the RCU for their supplied motors (i can't remember the technical reasons but I'll come back later).
 
This is probably what I call a "highly interlocked system", or at least the OEM considers it to be. What could be a result of somebody turning one or any motor on without any automatic control and then leaving it that way indefinitely?

An explosion? A fire? A catastrophic equipment failure?

If that's possible the OEMs lawyers will fight not only them installing the RCU, but fight you doing it too. But if your company has done their homework and your specs and purchase order and agreement are handled properly it'll be mostly a matter of getting their engineering dept to do the work. They may be aware of aspects of their equipment and control system design that they themselves distrust or dislike.
 
I'd be very leery of individual H-O-A switches on motors within a single piece of equipment such as your gas turbine. The whole package should have a single control switch, switches at each motor would simply be extensions of that single master control and would stop the whole package if not in auto. There probably isn't a safe means of manually operating any of the motor other than in automatic mode. Sometimes your standard spec needs to be coordinated with the realities of the equipment being specified.
 
From my experience, it is fairly common place to have a (LOCAL/AUTO/MCC)selector switch on the main control panel that you can switch to the required operation.Local to the motor then, a main isolator to make safe isolations with a stop/start to operate motor from there when local operation has been selected from main motor control centre (mcc). Or plc controlled when auto has been selected, or started from main panel if mcc selected on .
 
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