Thinking about three-phase power?

Tech Talk: So you are thinking about three-phase

By Troy Knutson, P.E., Distributed Generation Engineer at Cass County Electric Cooperative

Are you thinking about adding or upgrading to three-phase power?

Sounds easy enough, right? Just get an electrician to add a few wires and presto, you’re ready to go. We only wish it could be that easy. But there are some real issues to understand so you can make an informed decision before you jump into three-phase power.

So what is three-phase?

Without getting too technical, a good analogy for how three-phase power works on a motor is like rolling an oversized tire. Anyone who has rolled an oversized tire knows that it is difficult to get it started alone. Now try to imagine starting to roll the tire with the help of two other people. The tire is still the same size but it takes much less effort by each individual person because the work is spread out over three people. Three-phase acts on a motor in a similar way. It keeps a constant torque on the rotor. Lose one of the phases of a three-phase motor and it’s like rolling the tire with two people instead of three, it will still roll, but not as smoothly. Now this is not to say that single-phase motors have any lesser qualities than three-phase motors. If there were two identically sized motors one single-phase and one three-phase, the main difference would be that the single-phase motor would take more electrical current whereas the three-phase motor would get that current spread over three wires. More simply, three-phase motors can handle more power and start heavier loads. That is why three-phase is the most common set up for industrial and commercial services. Read more.

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