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jasonhe · Feb 21, 2010, 09:10 AM

Hi,

What is it that makes 3 phase power more efficient? Suppose I need an air compressor for a printing shop and I can choose between a 7.5HP single phase and a 7.5HP 3 phase.

Ignoring that the cost of the motor is a little less for 3 phase, why is the motor more efficient and how does this efficiency materialize? Does the electricity cost less if it is three phase? Or, does a 3 phase motor use fewer watts than a single phase? Or, is it something I am not even considering?

How can I quantify in dollar terms how much less it will cost to operate a 3 phase 7.5HP motor vs a single phase 7.5HP motor.

Thanks in advance.

Jason

InfoJunkie4Life · Feb 22, 2010, 08:34 AM

Three phase isn't necessarily more efficient, just more practical. A motor that uses 7.5 HP will require enough electricity to turn it at 7.5 HP. Three phase balance the load over three different supply lines propelling the motor three times per cycle, whereas single phase will only propel it one time per cycle drawing all of its power from one line. When it comes to industrial uses, three phase just makes sense. The motors can be built cheaper, and you can get a ton more power out of them, while when it comes to lighter use, it actually (in a lot of residential cases) costs more to have three phase, just run things such as fans, and even some heating devices.