At 01:26 PM 4/11/2010, Troy wrote:
>Just a quick question about switches: I need a switch that when
>toggled in one position will operates one appliance, and when
>toggled in the other position will operates a second, different
>appliance. Do I need a single pole double throw switch, or a double
>pole, double throw switch? I'm guessing the latter, but wanted to
>doublecheck. The SPDT

If you're operating both appliances from the same circuit then an
SPDT will do nicely; connect the supply to the center terminal.

If you're operating from different circuits or voltages then you need
a DPDT; connect each supply to one of the two center terminals.

Note that most switches don't have DC ratings unless they're intended
specifically for automotive use.  A decent rule of thumb is that the
switch should handle about the same number of amps at 12 v DC as it's
rated for at 110 v AC.

If you don't want to run heavy wiring to the switch, use a small SPST
switch to activate an SPDT (or DPDT) relay which will do the power
switching for you.  If you need a "both off" position it gets a bit
more complicated as the relay will have the NC contacts closed when
it's not activated.

Yours,
David