Ins and outs of hvac motors


Hvac motors are the sources of frequent problems and, therefore, frequent questions. Following are two questions and answers about motor operation:

Question: We're building some air-moving equipment for shipment overseas where the power supple is 240 volts but 50 Hz instead of 60. Will motor core saturation be a problem? How much tolerance should motors have?

Answer: Magnetically, the effect of going from60 Hz to 50 is about the same as a 20 percent increase in voltage. That's well above the National Electrical Manufacturers Association (NEMA) standard limit of 10 percent.

Locked-rotor current – and protection criteria – will be far outside normal limits. Core loss (and heating) also will be excessive, while the reduced motor speed will hamper cooling. Such an application is asking for trouble even if the horsepower load is reduced.