I bought an Old porcelain round rotary switch which I thought was single pole i.e. every time I turned the knob on top, the light would go either ON or OFF.
There are 4 terminals. When I connect 2 terminals (opposite each other) the switch behaves like single-pole as described above.
But this switch has 4 terminal, so I connected a second circuit to the other 2 terminals (double pole?). The results are when I turn the knob, one circuit goes ON and the other goes OFF. And each time I turn the knob the circuit that was ON goes OFF and the circuit that was OFF goes ON. There is no position when both circuits are ON or OFF together.
So, is this DPDT or DPST? also, does anyone know what a switch like this would be used for?
Best Answer
This is a DPST switch, but with one of the contacts normally open, as you'd expect, and the other contact normally closed. It's a bit of an oddity as a result -- it could be used as a 3-way switch, but that'd be silly compared to a normal (SPDT) switch.