Restaurant Equipment Buyers Guide : plugs

Typically, an electric utilitys distribution system begins at the substation, where three-phase lines with three separate lines branch out. The conductors on a three-phase power line are referred to as phases because each of the three carries electricity at a slightly different wave form or phase.

On a single phase service, there are two incoming 120 volt lines. On a three phase service, there are three.

There is a limit to the number and size of electric loads that a single-phase power line can supply. The need for three-phase service usually occurs where large motors are present. Up to a motor size of about 5 horsepower (hp), single-phase service is usually adequate. Beyond 5 hp, the single-phase line may have trouble delivering the current needed to start the motor. Starting a motor can require six times as much current as it takes after its running.