FAQs
What is the difference between a switch that is "Normally Open" and "Normally Closed"?
In general, Fire alarm control panels use "Normally Open" devices that remain open in a normal, non-alarm state, but close or "latch" when tripped, and remain latched (in alarm) until reset.
Most burglary zones and devices are "Normally Closed" where they remain closed in a normal, non-alarm state, but open to trigger an alarm.
You can also use your meter to verify that the N/O ("Normally Open") or N/C ("Normally Closed") device or switch is labeled correctly. Note also: The switch type is identified when the switch is in a non-activated and non-energized state.