- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
First off, forget the Line to Ground voltage or even the Line to Neutral voltage, all that matters in this case is the Line to Line voltage. If you have some unrelated issue with your Neutral connection or a difference in ground resistance from the neutral bonding point, that will show up in your L-G reading, But the motor is NOT using the neutral point, so the only thing that matters to it is the L-L voltage level.
People frequently throw around numbers indiscriminately when it comes to voltage ratings and voltage supplies. Officially (for what that's worth), the "Distribution" voltage for residential installations is 120/240V and officially, the "Utilization" voltage, which is what motor mfrs are supposed to design for, is 115/230V, which allows for some normal voltage drop from the source to the motor connections. NEMA MG-1, the design guide for motor manufacturers, also stipulates that motors should suffer no loss of performance or life expectancy as long as the voltage applied to them is +- 10% of the Utilization voltage. So that means a 230V rated motor can accept anything from 253 to 209V without a problem. That said, there are a lot of old motors out there which were designed before these "official" voltage levels were established, and then because of that, there are numerous lazy / ignorant foreign manufacturers who misread (or don't read) our standards and think that 220V is what we have. It's convenient for them because it makes it so they can sell their motors into places where the frequency is different and they don't have to derate them.
But... because there are also a lot of 208V installations for which the official Utilization voltage would be 200V, a lot of motor mfrs deal with it by making "208/230V" motors and they provide two separate FLC ratings at those two voltages. But there are no separate winding connections for the different voltages. What they do is design the motor for 220V +-15%. That way they are good for 253 - 200V.
What's important though is EXACTLY what your motor nameplate says. If it says "208/230V" it will be good to 253V line-to-line. If it says "220V 60Hz" on the nameplate very specifically, it is likely an older motor and it will NOT tolerate more than 242V line-to-line. If it says "220V 50/60Hz" it's likely a piece of Chinese junk.
People frequently throw around numbers indiscriminately when it comes to voltage ratings and voltage supplies. Officially (for what that's worth), the "Distribution" voltage for residential installations is 120/240V and officially, the "Utilization" voltage, which is what motor mfrs are supposed to design for, is 115/230V, which allows for some normal voltage drop from the source to the motor connections. NEMA MG-1, the design guide for motor manufacturers, also stipulates that motors should suffer no loss of performance or life expectancy as long as the voltage applied to them is +- 10% of the Utilization voltage. So that means a 230V rated motor can accept anything from 253 to 209V without a problem. That said, there are a lot of old motors out there which were designed before these "official" voltage levels were established, and then because of that, there are numerous lazy / ignorant foreign manufacturers who misread (or don't read) our standards and think that 220V is what we have. It's convenient for them because it makes it so they can sell their motors into places where the frequency is different and they don't have to derate them.
But... because there are also a lot of 208V installations for which the official Utilization voltage would be 200V, a lot of motor mfrs deal with it by making "208/230V" motors and they provide two separate FLC ratings at those two voltages. But there are no separate winding connections for the different voltages. What they do is design the motor for 220V +-15%. That way they are good for 253 - 200V.
What's important though is EXACTLY what your motor nameplate says. If it says "208/230V" it will be good to 253V line-to-line. If it says "220V 60Hz" on the nameplate very specifically, it is likely an older motor and it will NOT tolerate more than 242V line-to-line. If it says "220V 50/60Hz" it's likely a piece of Chinese junk.
