Stepping Switch

In electrical controls, a stepping switch, also known as a stepping relay, is an electromechanical device which allows an input connection to be connected to one of a number of possible output connections, under the control of a series of electrical pulses.

It can step on one axis (called a uniselector), or on two axes (a Strowger switch). Stepping switches were invented by Almon Brown Strowger in 1888. The major use for these devices was in early automatic telephone exchanges (commonly called Strowger or step-by-step exchanges or steppers) to route telephone calls. Later, they were often used in such equipment as industrial control systems.