two motors one overload

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gcasey

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I want to verify this before proceeding. I want to replace a single motor driving two fans with two motors driving to drive each fan. In this case I would need two overload units, one to protect each motor. I did not find anywhere in the code where I could protect both motors with one overload unit.
 
Dear
Is it reliable to have one thermal OL unit for two motors? Process-wise, is it ok to run one fan rather than two for short time whithin which you can rectify damaged motor if happened?

regards,
Riyad
 
Logically thinking this through, the FLA of both motors would have to flow through the 1 overload, so you would have to size that overload for 115-125% of both FLA's. If 1 motor was running and experienced an overload, the overload would not sense that due to you having to upsize that overload, resulting in a burned out motor and a violation of the NEC, from several parts of the code ( 430 & 110.10)
Additionally the motors are probably not UL listed to "Share" that overload.
Just my $.02
 
Without knowledge of the motor sizes in question here, I might also point out that the SCPD would possibly be the wrong size as well. It would have been sized for the conductors and/or single larger motor windings, but although the conductors may be the same, it's is likely too big for the now smaller motor windings.
 
davidr43229 said:
Logically thinking this through, the FLA of both motors would have to flow through the 1 overload, so you would have to size that overload for 115-125% of both FLA's. If 1 motor was running and experienced an overload, the overload would not sense that due to you having to upsize that overload, resulting in a burned out motor and a violation of the NEC, from several parts of the code ( 430 & 110.10)
Click to expand...

I agree.

Additionally the motors are probably not UL listed to "Share" that overload.
Just my $.02
Click to expand...

Many motors are not UL listed at all and are not required to be for many applications. :)

I think once you get into hazardous locations the motors have to listed.
 
What size motors are we talking about, anyhow? If you're going small enough to have thermally protected motors, you can just shunt the overloads in the existing starter.
 
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