What is the difference between a SPST vs DPST contact on a timer?
I need a timer for my typical pool motors that run on 240 VAC.
One is a filter pump, the other is a sweep pump.
It looks like I need a 2 pole switch with 2 "channels"; but not sure of the relevance of the contact type: SPST vs DPST
SPST means single pole, single throw. This type has one contact pair, and can control one leg of a voltage source.
DPST means double pole single throw. This type has two contact pairs, and can control two legs of a voltage source.
In both, the contact pairs move on the same armature, opening and closing at the same time.
If both motors come on and off at the same time, a DPST could be used, as long as it is sized to handle the total HP, voltage, and amps of both the motors. You would also have to fuse the line side of the relay correctly, and overload protect the motors on the load side. Easiest way to do this is get a motor starter sized to handle both motors.