It's a supervision issue. NC/EOL only gives you 2 states of the circuit. Open (alarm) and closed/EOLR (normal). It does give a limited trouble condition if the wire is shorted before the EOLR.
NO gives you all 3 states possible with an EOLR. There's a reason why a fire alarm and CO detector also use that as their detection method. Ability to supervise all states possible using a single EOLR (grounds are a different story).
NO gives you all 3 states possible with an EOLR. There's a reason why a fire alarm and CO detector also use that as their detection method. Ability to supervise all states possible using a single EOLR (grounds are a different story).
