Company FAQ's Contact Product Catalog


- What is 400HZ Electric Power?

- What does 400HZ mean?

- Why isn't 400HZ power more common?

- What is an inverter?

- How big is an inverter ?

- Can you use the inverter to eliminate the requirement of a

gearbox by reducing the RPM of the motor?

- Why not use Air Power instead of 400HZ power?

- How about hydraulic power?

- How many KW generator or inverter do I need to run a 25HP motor?


Q: What is 400 HZ Electric Power?
A: It is the type of electric power that is the standard of the commercial aircraft and aerospace industry because of its lightweight, its high power, and its proven reliability. Every time you fly in commercial airliners, the 400HZ power produced by the alternators on each engine power the overhead lights, air conditioning, heats your food, moves the landing gear up and down, rolls the wing flaps in and out, flushes the toilets, powers the radar, TV screens, radios, etc., etc. It is the primary power on all commercial and military aircraft.

Q: What does 400HZ mean?
A: The commercial power producers in the United States (the “Edison” Co’s) provide alternating current (A/C) power for home and industry. This power limits the RPM of the fastest induction motor to a maximum of 3,600 RPM. The maximum speed of a 400HZ induction motor is 24,000 RPM, approximately seven times faster than is possible with a 60HZ motor. This higher speed and the use of higher quality wire and lamination steel make it possible to produce motors with 10 times the power for the same weight and same size as a 60HZ motor.

Q: Why isn't 400HZ power more common?
A: Several Reasons!
(1) The only way to get 400HZ power from 1945 – 1970 was with an engine-generator or a motor-generator set.

(2) The cost of a 400HZ motor or generator was extremely high because of the aerospace specifications and necessary paper trail.

(3) Most people did not recognize that 400HZ power is basically identical in wiring and operation to a 3 phase – 240V Edison Company style power system.

(4) Since inverters have become available to convert 60HZ power to 400HZ power, 400HZ is growing much more quickly.

Q: What is an inverter?
A: An inverter is an electronic device that takes in 50HZ or 60HZ power and rectifies it to D.C. and then chops it back up into a different frequency, which in our case is 400HZ.

Q: How big is an inverter?
A: Today it’s very small. Our 15 KW inverters in their protective box with extra cooling fans are approximately the size of a large loaf of bread and weigh approximately two pounds per horsepower of output. They also provide ground fault protection, soft start capability, overload protection and variable motor RPM.

Q: Can you use the inverter to eliminate the requirement of a gearbox by reducing the RPM of the motor?
A: Yes and No! If you reduce the inverter frequency you can slow the motor but you reduce the horsepower of the motor. If you run your motor at 200HZ instead of 400HZ you will reduce its horsepower by half. It is better to use gears and keep full power to work faster.

Q: Why not use Air Power instead of 400HZ power?


(1) It takes a 100 horsepower compressor to make approximately 10 horsepower with an air motor.

(2) Lots of line loss when working far away from the compressor.

(3) Lots of noise from the motor exhaust.

(4) Lots of oil from the exhaust air.

(5) You will probably need an operating engineer to start and stop your air compressor if it is a portable unit.

Q: How about hydraulic power?
(1) Better power than air if work is close to power pack.

(2) Needs two heavy, oily hoses.

(3) Lots of line loss, long hoses suck up power.

(4) Machinery gets hot, oily and difficult to handle.

(5) Doctors do not like 55 gallons of hot hydraulic oil on the floor of the operating room.

Q: How many KW generator or inverter do I need to run a 25HP motor?
A: You can run a 25HP motor from a 20KW generator or 20 KW inverter. The generator will be in overload for a few seconds to start a 25HP motor, but it should start unless your power cord is too small or too long, lowering the motor starting voltage. An inverter will start your motor more easily as they have a built in motor starting ramp (soft start).

Most three phase induction motors take 3-5 times running amperage to start them without a “soft start”.


Copyright © 2008 400 Hertz Engineering. All rights reserved.   |  Privacy Policy