A fire alarm fuse spur or mains isolator is an electrical safety device that is used to protect a fire alarm system from power surges and other electrical issues. It is a type of electrical isolator that is installed between the main power supply and the fire alarm control panel. The fuse spur is designed to disconnect the power supply to the fire alarm system in the event of an electrical fault, such as a power surge, to prevent damage to the system and ensure the safety of the building's occupants.

A fire alarm fuse spur typically consists of a fuse and a switch. The fuse is designed to blow if the current exceeds a certain level, cutting off power to the fire alarm system. The switch allows the power to be manually disconnected in case of maintenance or testing.

It's important to note that fire alarm fuse spurs should be regularly tested and maintained to ensure that they are in good working condition and able to protect the fire alarm system in case of an electrical fault. It's also important to ensure that the fuse used is the correct rating for the fire alarm system and that it is replaced as needed.