O/L Protection of fractional HP motor

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bklauba

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I am working with an OEM that is planning on using a rotary electric vibrator, both 120, 60 Hz and 220, 50 Hz(these units outside US), both single phase. The application is upon portable powder dispensing equipment, mounted on a two-wheeled dolly. They have had some problems with reliability of the vibrators, and there is no O/L protection; just a switch in a switch box bolted to the cart. Amp draw of the vibrator is small: 0.25 amps.

Are there any code considerations here? We are encouraging them to use a small motor starter with thermal O/L relay, but they claim this is not required by any code.

Thanks for any help.
 
Re: O/L Protection of fractional HP motor

Most small single phase motors have some form of built in protection against overloads. That is why motors under 1hp are not required to have external overloads in many cases.

see 430.32(B) and (D)

Think about it - does your table saw have external overloads?
 
Re: O/L Protection of fractional HP motor

There is no O/L on the device itself, likely due to it's being a vibrator. Since the vibrator can see g levels of more than 2 - 3, sometimes more intermittently, this is a pretty poor location for an O/L.
 
Re: O/L Protection of fractional HP motor

I had an instance where a manufacturer supplied 120 volt, 1/4 hp motors without an internal thermal protector. They were used with a vent fan. Since a thermal device was not clearly required one was not provided. A separate overload had to be provided for these to protect the motor. You don't always get what you expect :)
 
Re: O/L Protection of fractional HP motor

For similar products that are single phase, we have found that the motor run or starting caps cannot be placed either in, or even near, the vibrator. The vibration degrades the caps' dielectric and they die an early death. An O/L mounted nearby would likely face the same problem, which probably explains why I have never seen one mounted in such a device, although they are prone to be overloaded in app. An onboard O/L would also be rather inconvenient, since these are often located either far out of reach, or buried in equipment. Whether more or less than 1 HP, overloaded these things can hotter than a two dollar pistol.

But since no O/L is required, due to it's being less than 1 HP, this seems to be an app that falls between the cracks of the NEC (maybe). In our opinion, the gear should have an O/L, but the OEM is using the code to deny its need.
 
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