Several of the sensors I'm looking at are available with a Form A relay (SPST, normally open), and are usually less costly than cases where the same unit is also available with a Form C relay (SPDT, make-before-break).
The cost difference is more than can be explained by the differences in the relay, so I'm guessing that means the Form A model has higher sales volume.
From a security system design perspective, what is the attraction of a Form A relay (let's say for the sake of argument it is on a motion detector, and you are wiring a zone with four of these detectors having a Form A relay)?
Unless I'm looking at this wrong, it seems it would be preferable to have a Form B (SPST, normally closed) relay be the default configuration sold, rather than a Form A. I don't find *any* with a Form B relay, so I must not be looking at this right.
The cost difference is more than can be explained by the differences in the relay, so I'm guessing that means the Form A model has higher sales volume.
From a security system design perspective, what is the attraction of a Form A relay (let's say for the sake of argument it is on a motion detector, and you are wiring a zone with four of these detectors having a Form A relay)?
Unless I'm looking at this wrong, it seems it would be preferable to have a Form B (SPST, normally closed) relay be the default configuration sold, rather than a Form A. I don't find *any* with a Form B relay, so I must not be looking at this right.