Question about NC vs NO door sensor


Active Member
The GRI RB-02 roller ball sensor can be be bought in a NC configuration, which I always thought was best for entry/exit doors, windows, etc. The problem is that they seem to be in very short supply, e.g., 6 to 7 week lead time. GRI also manufactures a DS-01T roller ball sensor (with wire terminals instead of leads) that has almost identical spec's to the RB-02, except that it is only available as a NO SPST switch or a SPDT switch (which only comes with leads, and is also hard to find).

The M1 doc diagram shows zones can have either a NC or a NO sensor, and shows the differences in wiring with an EOL resistor, but it doesn't suggest one is better than the other, or one has less "features" than the other. Assuming both are wired correctly with an EOL resistor, is there any benefit to one over the other?

As long as you have EOL resistors, that provides supervision of the zone and a NO contact is just as good as a NC.