Switch Definitions NC Normally Closed ON NO Normally Open OFF ( ) Momentary Action SPDT Single Pole Double Throw 2 or 3 Positions SPST Single Pole Single Throw 2 Positions 3PDT Three Pole Double Throw 2 or 3 Positions 4PDT Four Pole Double Throw 2 or 3 Positions DPDT Double Pole Double Throw 2 or 3 Positions DPST Double Pole Single Throw 2 Positions NO/NC 3 Poles Wired either/or Rotary Poles then Positions