The DPDT (Double Pole Double Throw) switch consists of two SPDT circuits located internally within the switch housing. Additionally, a common lever mechanism inside the housing actuates both circuits in tandem. Typically, a DPDT mechanical switch has six terminals: two C (Common), two NO (Normally Open), and two NC (Normally Closed).
What’s the difference between SPST, SPDT and DPDT?
13 February 2025
SPST, SPDT, and DPDT are abbreviations for different types of switches that are defined by their number of poles and throws. Relays are electromechanical switches that use an electromagnetic coil to control the switching of one or more electrical contacts. People commonly use them in various applications to control high-power circuits with low-power signals.
A relay consists of an electromagnetic coil and one or more sets of electrical contacts. When current flows through the coil, it generates a magnetic field, which attracts or repels the contacts, causing them to open or close. Relays are classified by their number of poles and number of throws. The pole of a relay is the terminal common to every path. Each position where the pole connects is called a throw.
So what is the difference of SPST, SPDT, and DPDT?
The SPST (Single pole single throw) mechanical switch has two terminal connections – the NO (Normally Open) and the C (common). When the switch actuates, it closes the circuit, and current flows from the common terminal through to the normally open terminal. When the SPST mechanical switch remains unactuated, it keeps the circuit open.
The SPDT (Single pole double throw) switch has three connections – the NO (Normally Open), NC (Normally Closed) and the C (Common). Input current enters the switch through the common and makes the circuit either with the NO (normally open) or the NC (normally closed) contacts.
