I’m wiring two reed switches to detect open/close for my garage doors. The reed switches support NO or NC wiring. After thinking about it, wiring both in series and using NC seems the most fault tolerant, as the zone will show the doors as open if a wire was cut or a switch had an issue. It seems a lot of the alarm world took this approach as well with the preference for NC door sensors.
However, I found this guide from the Konnected docs recommending NO for door contacts, while also showing diagrams with the contacts wired in series. NO contacts wired in series doesn’t seem to make sense to me, as one door opening won’t actually close the circuit so it won’t be detected, they should be wired in parallel for NO or use NC when wired in series. Am I understanding that correctly?
I guess I’m just confused about what Konnected recommends and also wondering if this documentation is incorrect or I’m not understanding a key concept here.
I think you’re thinking about it backwards. Normally Open (NO) means that the circuit is open in the “normal state” and the circuit is closed when the magnetic piece is present and the reed-switch activates. This is how the vast majority of door sensors work. When the magnet is close to the sensor, the circuit is closed. When the magnet is away from the sensor, the circuit is open. When the sensor wire is cut, the circuit is also open.
Wiring sensors like this in-series means that they all have to be closed (magnet present) in order to report closed. If any one sensor is open, the entire circuit is open.
Either NO or NC will work, but NO is by far the common standard.
Interesting, seems the confusion then is what is considered the normal state? Maybe I’m seeing a variation in how different brands mark their normal state. For some the normal state is when the magnets are together, and for others when they are apart. Have you seen that at all?
I feel like it’s a pretty standard definition though. Google it for more context. The “normal” state means the state at rest, when NOT influenced by a magnet or actuator.