Why Watts? TT5
Published on May 12, 2014

Why Watts?
Tech Talk 5

You know how you can tell what people know by the questions they ask? Well, we know that most people don’t know about watts. They ask, "How many amps does this motor use?" instead of, "How many watts does this motor use?" Watts are what you pay for, not amps (amps are used to size breakers, etc.).

The direct current formula we all learned (volts x amps = watts) is correct for incandescent light bulbs and electric heaters, but it is not correct for motors. When dealing with power loads that involve inductance magnetic devices such as motor windings, solenoids, transformers, lamp ballasts, etc., the formula for single-phase loads is volts x amps x power factor = watts.

In many cases, especially with linear air compressors and mag drive pumps, the actual watts used are significantly less than what is calculated by multiplying volts x amps. The only way to determine the watt consumption of a motor is to test it using a wattmeter.