Keep in mind when reading any article about electrical theory or application that it only scratches the surface of the topic. You can dedicate years of your life to understanding electrical theory and design the way many engineers do and still know just enough to be dangerous. In HVAC, we rarely need to have a deep understanding of electrical design. But there are a few cases where a little understanding can go a long way in identifying issues before they cause trouble, and that is the intent of this short article.
Power is generated at the utility in three phases that are 120 degrees out of phase with one another at 60 Hz. This simply means that 60 times per second, each individual leg of power makes one peak and valley (a full circle), and all three of the phases together split the cycle into thirds (trisect).