I have a client that wants to run some single phase 1/2 HP sump pumps from the normal power and with an backup generator. The normal power is 120/208 and these motors run at 208 volts. They want to use a single phase 120/240 volt generator for the back-up power. The motors would then run at 208 volts for the normal power and at 240 for the back-up. The motors are probably 115/230 volt but I don't know for sure. If they are 230 volt motors I don't see a problem since either voltage is within the tolerance for the motor (assuming these are typical motors). Does anyone see a problem?
motor 208 or 240
- Thread starter bsh
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- Lockport, IL
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You would only be within tolerances if the manufacturer says you are within tolerances. If the motor is rated for the voltage range of 208 to 240, then you will be OK. But if it only says 230 volts, I would not run it at 208. For starters, a 208 volt system can have a voltage below 208 by a few percent or so. That would put you more than 10% below the motor's rating. That would, in turn, cause the current to be high, and the motor to run hot. Since this is the condition it would be most of its operating life, it would wear out early.
wasasparky
Senior Member
If the motor is 230V (likely), you may want to incorporate a buck/boost anyway...
If the motor is 208V, calculate the expected voltage drop from the generator. You may once again want to consider buck/boost...
If the motor is 208V, calculate the expected voltage drop from the generator. You may once again want to consider buck/boost...
The big issue will be current draw.
If the motor is truly 208 volt rated, it will draw the rated current at that voltage. If the voltage is increased to 230/240V, the current draw will decrease.
I don't know of any motor manufacturers who would have heartburn over this, especially since the increased voltage would not necessarily be on a regular or continuing basis. Many motors have a 208/230 or 240 volt rating anyway.
Good luck!
If the motor is truly 208 volt rated, it will draw the rated current at that voltage. If the voltage is increased to 230/240V, the current draw will decrease.
I don't know of any motor manufacturers who would have heartburn over this, especially since the increased voltage would not necessarily be on a regular or continuing basis. Many motors have a 208/230 or 240 volt rating anyway.
Good luck!
There should be no issue whatsoever.
Many motors are rated 208-230/240v. If you are running at 208V and the generator output is 230/240V, as long as the motor controller is electromechanical and not electronis, the only effect you should see is a decrease in the current when running on the higher voltage.
Good Luck!
Many motors are rated 208-230/240v. If you are running at 208V and the generator output is 230/240V, as long as the motor controller is electromechanical and not electronis, the only effect you should see is a decrease in the current when running on the higher voltage.
Good Luck!
Rick Christopherson
Senior Member
If these are dual voltage motors and only 1/2 hp, then you should be reconfiguring them for 120 volt operation, and that way, it is a non-issue.
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For what it is worth if the 208 volt generator is there to supply the emergency egress lighting you can not just decide to add sump pumps to it.
If the generator is an 'emergency' generator you must comply with 700.9(B).
If the generator is a 'standby' generator all you need to worry about is the load.
If the generator is an 'emergency' generator you must comply with 700.9(B).
If the generator is a 'standby' generator all you need to worry about is the load.
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