Single Pole Single Throw (S.P.S.T.)
On/Off
Single pole single throw switches control a single wire circuit
(Two terminals on the switch)
Example circuit: a light switch - On/Off
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Single Pole Double Throw (S.P.D.T.)
On/Off/On
Single pole double throw switches control two (double) single wire circuits permitted only one circuit to be energized at a time
(Three terminals on the switch)
Example circuit: Dual fuel tank this circuit or that (not both)
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Double Pole Single Throw (D.P.S.T.)
On/Off
Double pole single throw switches control two circuits simultaneously. Circuits are ON at the same time, OFF at the same time. Like two separate single switches together. Voltage can be from two separate sources.
(Four terminals on the switch)
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Double Pole Double Throw (D.P.D.T.)
On/Off/On
Double pole double throw switches control four circuits, permitting only two circuits to be energized at a time
(Six terminals on the switch)
Example circuit: Dual fuel tanks and dual fuel pumps (left tank gauge and left pump, etc) input voltage can be from two separate sources (fuses) 1 from fuel gauge and one from fuel pump (L and R)
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