Standard Decrement Curves

For circuit breaker and relay application, it is frequently necessary to determine the decrement in power system short-circuit currents. For this purpose certain ``standard decrement curves´´ approved by the National Electrical Manufacturers Association have been in general use. The original curves appeared in 1918 and a revised set was prepared in 1923. New decrement curves given in the present paper supersede those formerly in use. The paper also includes a discussion of the need for new curves, the underlying assumptions upon which they are based, the method of application and their limitations.