Single-phase alternating current rises from a negative voltage to a positive voltage before falling back to a negative voltage again, repeating the cycle 60 times every second. This type of electrical power is commonly supplied to residential and commercial buildings because it is well-suited to light electrical loads for lighting and small to medium appliances and tools.
Single-phase motors become increasingly inefficient as they grow larger and require higher currents to operate. The limitations of residential electrical power coupled with the inefficiency of single-phase motors makes them impractical for higher power applications. Motor manufacturers make small, single-phase motors for residential and commercial use, and large three-phase motors for industrial use.
Large Single-Phase Motors
The largest single-phase motors suitable for residential use top out at 10 horsepower. A few commercial applications may be found for higher voltage single-phase motors at up to 15 horsepower, but these are rare and require 480 volts of single-phase current to operate. Three-phase motors are much more efficient and manufacturers make them in ratings of hundreds of horsepower.