What is the difference between 50, 60, and 400 Hz ?

Most AC (alternating current) relays operate on standard frequencies and voltages.

50 Hz FREQUENCY : This is a standard alternating current frequency used mostly in Europe, Africa, Australia and Asia, Voltages commonly used with this frequency are: 115VAC 10, 115/220 30, 220VAC 10, 220/440 30.

60 Hz FREQUENCY : This is a standard frequency used primarily in the USA and Canada, but it is also used in many other countries. The typical voltages used in households and industries are 115VAC 10, 115/200 30, 220/400 VAC. In some instances heavy industry will use 440/660VAC 30.

400Hz FREQUENCY : This is a standard frequency used in most commercial/military aircraft. It is also used on Navy aircraft carriers, but primarily to service aircraft. Most aircraft utilize the 115/208 VAC 400 Hz WYE system, except some newer aircraft, which use 230/400 VAC 400 Hz because of its lighter weight generator system. The 400 Hz frequency is used in aircraft systems primarily because the generators are much lighter in weight. 50/60 Hz frequencies are used because that was the chosen frequency by the federal government years ago, and no one has upgraded the frequency because of the associated cost.