Taylorwoorobertson
Member
- Location
- Kansas
I have a 15 HP 3 phase motor 120/208 v...What are the full load amps?
3 Phase Motor Question
- Thread starter Taylorwoorobertson
- Start date
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- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Based on T. 430.250 it is 46.2 amps
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
odd - my chart says 48.3.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
That's 200V
Taylorwoorobertson
Member
- Location
- Kansas
Does the fact that it is 120/208 make a difference vs 120/240?
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Yes it does. The nec tells us to use the tables in the book. 3 phase 208V 15 hp is 46.2 amps
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
By the way, forget the 120V issue, the motor couldn't care less about the phase to neutral voltage, you are just going to confuse yourself. If you have a 208Y120 3 phase 4 wire system, your 3 phase motor voltage is 208V.
But because you worded it that way, I'm thinking you are looking at your LINE voltage, not the motor voltage. What does the MOTOR nameplate say on it? It will not say "120/208V" for sure, it will say 200V, or 208V, or or 230V, maybe 208/230V. That will make a difference in what the FLA is, as far as if you are calculating something about the MOTOR.
If however you just want to know for the purpose of selecting conductors, then as was said, you use the tables in the NEC, even if the motor nameplate says it is less.
Is this a test question? Where did you ever get a 120/208 motor?
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
I did not take the OP to mean the motor was 120/208 but that that was the system voltage
As stated:
"I have a 15 HP 3 phase motor 120/208 v...What are the full load amps?"
120/208 also more correctly stated should be 208/120 or 208Y/120 should that be a system voltage. The motor should be 208v, 3ph.
This appears to be a test question since the OP does no appear to be versed in the correct terminology. As quite often happens we often drag our answers out by having to ask numerous follow-up questions in order to find out what should have been included in the OP.
Thus, based upon our interpretation of the question our answers may be regarded as gospel by the OP but would be a wrong answer based upon what the actual application is. As such our responses may be very likely incorrect which may create a safey issue.
I do agree that this example is very simple, that it should not be an issue other than the question being incorrectly stated and appearing to be a test question.
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