Motor Overload Protection through Transformer

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dlbarker2

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I'm reasonably certain it's not a good thing to do, but not sure what will occur: The designed called for the six fuel pumps on a multiple generator installation to be 120 volt, and the system was wired and installed to match this design. The fuel pumps were only available as 208 volt single phase. The contractor is suggesting rather than changing out the branch circuit breakers, the contactors, and motor overloads (all rated 130 volt), just add a 3 kVA, 120 - 208 volt, single phase transformer after each of the six individual contactor/motor overloads. The motors are only a 400 watt load. Placing a transformer between the motor and the motor overloads seems like a really bad idea, and not sure how you'd size the overloads, or whether they would provide the protection intended. Any experience out there would be appreciated.
 
dlbarker2 said:
I'm reasonably certain it's not a good thing to do, but not sure what will occur: The designed called for the six fuel pumps on a multiple generator installation to be 120 volt, and the system was wired and installed to match this design. The fuel pumps were only available as 208 volt single phase. The contractor is suggesting rather than changing out the branch circuit breakers, the contactors, and motor overloads (all rated 130 volt), just add a 3 kVA, 120 - 208 volt, single phase transformer after each of the six individual contactor/motor overloads. The motors are only a 400 watt load. Placing a transformer between the motor and the motor overloads seems like a really bad idea, and not sure how you'd size the overloads, or whether they would provide the protection intended. Any experience out there would be appreciated.
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Wow, the things people come up with to try and save a few bucks. I rarely deal with single phase motors but it would seem to me that you would not save all that much money after buying all those transformers.
 
Using a 3kva, transformer will give you many times more inrush current than if you sized the transformer for the load, and might possibly pre trip the OL's, a .5kva transformer would probably work ok as long as you resize the OL's for the added wattage, if the OL's were sized for the HP of the motor or FLA at 120 volts, then they will be just a little low with a .5kva transformer in line.

But all in all a check with the manufacture of the pumps would be best to see if this would void there warranty.
 
dlbarker2 said:
...just add a 3 kVA, 120 - 208 volt, single phase transformer after each of the six individual contactor/motor overloads. The motors are only a 400 watt load. Placing a transformer between the motor and the motor overloads seems like a really bad idea, and not sure how you'd size the overloads, or whether they would provide the protection intended. Any experience out there would be appreciated.
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Don, don't do this. The motor stipulates the circuits here, change the motors or supplies.
 
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