Electronics specification and abbreviation Expansion
of
abbreviation
British
mains
wiring
name
American
electrical
wiring
name
Description Symbol
SPST Single pole, single throw One-way Two-way A simple on-off switch: The two terminals are either connected together or disconnected from each other. An example is a light switch.
SPDT Single pole, double throw Two-way Three-way A simple changeover switch: C (COM, Common) is connected to L1 or to L2.
SPCO
SPTT, c.o.
Single pole changeover
or
Single pole, centre off or
Single Pole, Triple Throw
    Similar to SPDT. Some suppliers use SPCO/SPTT for switches with a stable off position in the centre and SPDT for those without.
DPST Double pole, single throw Double pole Double pole Equivalent to two SPST switches controlled by a single mechanism
DPDT Double pole, double throw Equivalent to two SPDT switches controlled by a single mechanism.
DPCO Double pole changeover
or Double pole, centre off
    Equivalent to DPDT. Some suppliers use DPCO for switches with a stable off position in the centre and DPDT for those without.
    Intermediate switch Four-way switch DPDT switch internally wired for polarity-reversal applications: only four rather than six wires are brought outside the switch housing.