SPST stands for?

• A. Single-pole, single-throw.
• B. Single-pole, double-throw.
• C. Double-pole, single-throw.
• D. Single-throw, double-pole.

Answer: (A)

Think of SPST as the simplest switch that controls a single circuit. It has one pole (one moving contact) and one throw (one fixed contact), so it can either close to complete the circuit or open to break it. That’s why SPST stands for single-pole, single-throw—a basic on/off control.

If a switch were single-pole, double-throw, it would connect the same input to one of two outputs, which isn’t SPST. A switch with two poles would control two separate circuits at once, called double-pole, single-throw. The phrasing single-throw, double-pole isn’t a standard way to describe SPST.