fire alarm systems where the strobes fail to flash.

I’ve seen them occasionally. Why would that be? I was once at a school, the fire alarms started going off, however none of the strobes were doing anything.

Sounds like in this case it’s a NAC issue. I’ve seen some similiar occurances, but nothing quite directly as similiar as this.

What’s NAC stand for?

NAC stands for Notification Appliance Circuit, also known as a signal circuit or bell circuit.


At my high school, one of the Simplex 9219’s did not flash - an issue which started occurring during my senior year.

Also, at the dining center at my college, the SHG’s flash at just about 1 Hz, except for one, which flashes every few seconds. Not sure why.

It could be a number of things. The synch type for the NAC may not be set right at the panel, it could be a bad synch module (in the instance that the panel does not provide or is not capable of providing synch). Could also be that the visible component input on a power supply is disconnected or disabled (this could also apply to a synch module) just to name a few. Also if it is an audio evac system the strobe circuits are ran from a completely different set of equipment than the speaker circuits, and the speakers can be independently ran and tested from the strobe circuit and vice versa.