208V vs 230V Motors TT39
Published on May 12, 2014
 

208V vs 230V Motors - Tech Talk 39

A motor that is rated for 230 or 240 volts is not compatible with 208V power. The motor will fail and will not be covered by warranty. When it fails depends on how well the motor was built, how hard it is working and the actual voltage that is getting to the motor. If you only have 208V power and can't find a motor that is rated for it, you can install a "buck-boost transformer" to raise your voltage.

Most—but not all—AC motors are built to tolerate a 10% up or down voltage variation from what is shown on the motor nameplate. A motor labeled as 115V can operate reliably between 108 and 132V. The range for 208V motor is 187 to 229V. The range for 230V is 207 to 253V. After reading these ranges you might think, "A 230V motor can work at 208V." That would be true if your service always gave a minimum of 208V. But it will not because of "voltage variation." For instance, if your service is 208V, you will experience normal voltage variations as low as 187. This is why some 230V motors operate on 208V service for a while, then, when other equipment starts up, the voltage drops below 207 and the motor draws more amps, overheats and fails.

Buck-boost transformers reduce (buck) or raise (boost) supply voltage to the required level. A common application is boosting 208V to 230V.

If your motor is a long distance from your power meter you will also incur "line losses." These will show as lower voltage and higher amperage at the motor. To be sure your installation is correct, always measure the volts and amps at the motor location, while it and everything else on that line is operating. Both must be within the motor label's specifications. See Tech Talks 5, 10 and 11 for more information.