Electriman
Senior Member
- Location
- TX
Is there any chart or table that determine the VA rating of electric motors or should I use NEC tables and multiply the current by voltage?
VA rating of Electric Motor
- Thread starter Electriman
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ptonsparky
Tom
- Occupation
- EC - retired
I think you’re looking for KW. 760 watts per Hp was schoolbook IIRC.
746. I have been corrected.
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Single phase or three phase?
That will give output power. Maybe the OP wants to get input kVA.
Electriman
Senior Member
- Location
- TX
Both
Electriman
Senior Member
- Location
- TX
No. I am looking for VA or (KVA).
Electriman
Senior Member
- Location
- TX
That is right.
OK.
For single phase you can take the product of nameplate Volts and Amps for input VA.
For three phase you need sqrt(3) times the Volts and Amps.
winnie
Senior Member
- Location
- Springfield, MA, USA
- Occupation
- Electric motor research
It will change with load and applied voltage.
But simply multiplying volts times amps gives you VA. For 3 phase use amps * volts (line-line) * 1.732.
-Jon
But simply multiplying volts times amps gives you VA. For 3 phase use amps * volts (line-line) * 1.732.
-Jon
That's why I mentioned nameplate data. That doesn't mean it will necessarily run at that at all times. Loading may be cyclic for some applications.
Electriman
Senior Member
- Location
- TX
Ok. Thanks. I thought there might be a table similar to NEC 430.250 for VA. I guess I can make it using the formula.
pjones
Member
- Location
- Vancouver Canada BC
I’m guessing the motor amperage should be multiplied by the service factor first to get the maximum possible amperage it could possibly see in normal use.... thoughts on this?
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Service factor is not something we come across on this side of the pond. Continuously maximum rated (CMR) is normally what we use. Sometimes, an intermittent short term rating is given for particular applications.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
I would use the NEC tables for current (with the appropriate exceptions), then calculate kVA based on the normal formula for single or 3 phase.
It’s not a good idea to use Service Factor continuously. It CAN be done and is often done by machinery OEMs in order to avoid having to buy a larger motor, but just because you can, doesn’t mean you should. The end user is who has to live with the long term consequences because the motors will likely outlast the OEM’s warranty.
It’s not a good idea to use Service Factor continuously. It CAN be done and is often done by machinery OEMs in order to avoid having to buy a larger motor, but just because you can, doesn’t mean you should. The end user is who has to live with the long term consequences because the motors will likely outlast the OEM’s warranty.
pjones
Member
- Location
- Vancouver Canada BC
I’m not saying it should be done either but since it is a tolerance that is allowed to be used and without knowing what the application this information is being applied to I thought it would be safest to assume it might be used.
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