Understanding Electric Motors

Knowing the differences between US and foreign electric motors, their voltages, and how to convert between them is key to connecting and using the motors correctly.

Motors in the United States use two windings, which results in dual-voltage electric motors. The two motors are connected in parallel for low voltage or in a linear series for high voltage output. US electric motor voltages have a ratio of 2:1, for instance 230/460 volts.

Foreign mo tors, such as IEC motors, generally use one winding. This winding is connected in a delta for low voltage or a wye for high voltage. Three-phase electrical systems have a wye: delta voltage ratio of 1.732:1, for instance 220/380 volts. The higher voltage number is always a wye connection. This system makes connections easier because they involve only six motor leads instead of the US-standard nine leads. You can have 12 leads in either the American or the foreign motors if the motor is sizable enough to need reduced-voltage starting.

IEC voltages are usually given at 50 Hz rather than the 60 Hz common in US power systems. To convert between US and IEC voltages, increase the IEC voltage by 20 percent to equal the 60 Hz American rating.

Example:

You have a 220/380 volt rating. These are 50Hz voltages and will be so indicated on the motor nameplate. To convert them to 60 Hz equivalency voltages, increase the 50 Hz IEC voltage by 20 percent. This gives you 264/456 volts, the 60 Hz American equivalent to 220/380 50 Hz voltage in the IEC voltage.

However, 264 volts does not exist in the US. The 456 voltage is very close to the US 460 voltage, so this is the voltage connection appropriate to use. Because the higher voltage is always a wye connection, this provides the information needed to connect and correctly use the motor on the appropriate voltage, rather than looking for a reduced voltage starter.

Very few companies build and export electric motors for use in the United States & Canada. WEG is one of the largest electric motor manufacturers in the world and the largest producer for the US market. WEG was founded in 1961. The company now employs 22,000 people in over 1 million square meters of constructed manufacturing space. WEG offers a diverse range of IEC/NEMA certified motors in low, medium and high voltages suitable for every application.