Do they ring when the fire alarm in a building goes off? Or do they only ring if a sprinkler activates?
In most cases they will only activate if water is actually flowing in the sprinkler system. Older bells were actually directly water-driven, while most nowadays are electric bells wired into contacts on a waterflow switch.
Sprinkler bells can be wired one of several ways:
1.) 120VAC bell wired directly to the second set of contacts on the waterflow switch - completely isolated from the FACP
2.) 24VDC bell wired directly to the second set of contacts on the waterflow switch - 24VDC power comes from the constant power of the FACP
3.) 24VDC bell wired to its own NAC - NAC only activates with waterflow switch activation (or) NAC activates under general alarm
4.) 24VDC bell wired to a control module of an addressable system - Control module only activates with waterflow switch activation (or) Control module activates under general alarm
5.) 24VDC bell wired to a NAC with other horn/strobes, strobes, etc in the building
There aren’t any specific code requirements to wire them up any particular way, at least around here, it’s whatever the designer or FM wants.
Option 1 is good because if there is a total failure of the fire alarm system, the bell will still ring
Options 2, 3a, & 4a are good because the bell will only go off if there is flowing water - FD pulling up to the scene knows the sprinkler system is operating and possibly controlling an active fire
There are water motor gongs but they are not an electrical device.