Let’s say I had two zones with 4-wire smoke detectors. The resettable power circuit they’re connected to needs to be supervised. Could you just put a supervision relay in-series with one zone?
You could use a DPST relay to indicate a trouble on both of the affected zones should detector power be lost.
I have no idea how this idea would hold up in a real installation… but for a hobby system it should work fine.
In a hobby system you can do whatever you want.
In a real world situation an end of line relay would be needed in each zone. Running two power circuits with a relay only at the end of one leaves the second power run unsupervised.
The only way to provide complete power supervision with one relay would be to power zone one smokes then double back the power wiring to the panel then power zone two smokes and put a relay there. This complicates troubleshooting since a power wire break in zone one would indicate trouble in zone two. That also may not pass an AHJ inspection. Doubling back the power wiring increases the wiring cost. That also may require larger conduit on that zone which is another cost increase. The second relay would be much cheaper and easier.
So if you get the second relay, then you can just run two separate circuits out of the resettable power terminals?
Think of it this way, you are not supervising JUST the 24V output for the panel, you are supervising EACH individual circuit. And you are supervising for loss of 24VDC power from the panel or a disconnected wire (or device) within the circuit. Theoretically, you should have the same number of wires under the 24V resettable power as you have zones with 4-wire devices. So in your setup, you would have two red wires on the positive, two black wires on the negative. Each 4-wire zone should consist of a end of line power supervision relay and resistor at the last device.
Thank you! That was very helpful!