Home Forums General Discussion Technical Questions Shunt trip disconnect question

If the heat detector/ fire alarm that activates the shunt trip disconnect loses power or gets damaged/ripped off ceiling should the shunt trip activate or should it just send trouble to the fire alarm panel? Can't find anyone that knows this in field.

The circuit should be monitored by the fire alarm panel and send a trouble warning if the power activating the shut is cut off. The monitoring point of the must be within 6’ of the shunt device. As far as the shunt going off , it by code could be wired either way fail safe or fail secure so to speak, but I’ve never seen anyone wire it where loss of power would kill the elevator. Doing so while code complaint , does not elevate the need for the monitoring circuit. It does however lead to the potential of more entrapments and isn’t good practice. But again I’ve never seen it wired that way, I can’t think of a shunt manufacture for whom it is even an option.

Nfpa 72 21.4.5 Says loss of voltage to control circuits shall cause a supervisory signal. This intimates that power is always to be available, so circuit is always fail safe hot. When heat detector closes, or fire alarm panel initiates, it need to shunt. Shunt coils by design shunt when power is brought to it, not when it's removed.

NFPA 72 21.4.6 the devices used to initiate shunt shall be monitored for integrity by the fire alarm panel. So if heat detector gets used, or knocked off the wall, panel should read a supervisory closed, or open circuit trouble.