motor controller as overload protection

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mbarry

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When using a manual motor controller for overload protection can the hp rating of the controller be less than the motor as long as it can be set for flc of motor.
example: 460v-15hp pump @ 3450rpm = 18.2fla
Which of the following controllers should be used?
1) rated 10hp@460 with setting range 16-20amps.
2) rated 15hp@460 with setting range 20-25amps.
 
raider1 said:
Take a look at 430.83.

Chris
Click to expand...
Chris,
That's what has me confused. according to 430.83 I should use the 15hp controller. But,the controller manufacturer's instructions say to set dial for motor fla.
I believe they are getting thier values from table 430-150.
 
mbarry said:
Chris,
That's what has me confused. according to 430.83 I should use the 15hp controller. But,the controller manufacturer's instructions say to set dial for motor fla.
I believe they are getting thier values from table 430-150.
Click to expand...

You are permitted to set you overload protection at 115% of the motor nameplate rating. So using your example of a motor FLA of 18.2 amps I come up with an overload setting of 20.93 amps which is avaliable on the 15 HP rated controller.

Also if you motor has a service factor of 1.15 or greater or is marked with a temperature rise of 40 degrees C or less you are permitted to size your overloads at 125% of the motor nameplate full load current.

Take a look at Part III of Article 430.

Chris
 
Chris,
Thanks for the information and code references.
The application is a UL508 custom control panel.
Does that make any difference in the answers?
 
mbarry said:
Chris,
Thanks for the information and code references.
The application is a UL508 custom control panel.
Does that make any difference in the answers?
Click to expand...

Yes, now you must follow UL508A instead of the NEC. The UL inspectors I have dealt are very more strict, especially when it comes to ignoring information on other UL Listed components.

And, I know the NEC has allowances for sizing overloads but, you must follow your manufacturer's instructions. For example, Square D says to size their thermal units (melting alloy style) to 100% of the nameplate FLA, any service factor increase has already been accounted for in their tables.
 
Jim,
I don't my UL508A handy, but I believe it says to set overload for full load current.
So, I guess the question is which takes priority flc or hp?
 
There are two issues here. The rating of the controller and the rating of the overloads. You have to comply with the rules for both. In general 430.83(A)(1) requires that the controller have a horsepower rating equal to or greater than the motor horsepower.
The UL standards can't over rule this requirement if this is an NEC installation. If the overload for the controller with the correct hp rating can't be set low enough to protect the motor, it sounds like a design flaw on the part of the controller manufacturer.
 
Which of the following controllers should be used?
1) rated 10hp@460 with setting range 16-20amps.
2) rated 15hp@460 with setting range 20-25amps.
Click to expand...

Why would you only use / solve or go with a minimum voltage of 460V ?
Granted it might be all work at 460V but your protecting the service that its supplied from 480V, is this also across the pond ?
 
cadpoint said:
Why would you only use / solve or go with a minimum voltage of 460V ?
Granted it might be all work at 460V but your protecting the service that its supplied from 480V, is this also across the pond ?
Click to expand...
Even US motors are rated as 460V. It is a quirk of our industry that motors are listed for a utilization voltage rather than the system nominal voltage.
 
don_resqcapt19 said:
There are two issues here. The rating of the controller and the rating of the overloads. You have to comply with the rules for both. In general 430.83(A)(1) requires that the controller have a horsepower rating equal to or greater than the motor horsepower.
The UL standards can't over rule this requirement if this is an NEC installation. If the overload for the controller with the correct hp rating can't be set low enough to protect the motor, it sounds like a design flaw on the part of the controller manufacturer.
Click to expand...
I agree with this opinion.

NEC tables show 15HP 460V at 21A. Ideally, if you are the manual motor controller mfr, you want the FLA of your HP rating to fall somewhere in the middle of the adjustment dial in order to allow for differences in motor designs, # of pole etc. But a mfr must also rate a device for it's switching capacity, i.e. making and breaking under load. Most likely, that particular mfr's 16 - 20A device failed the switching duty rating of a 15HP motor, otherwise they would have used it. It's a common problem for IEC manufacturers who's devices were not designed for HP rated NEMA motors, but rather IEC kW rated motors. The standard kW ratings don't line up perfectly to NEMA HP ratings.

You need to find a different manufacturer of manual motor starter, this one does not have a product that you can use.
 
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