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Fire detection and alarm circuits
Chapter 56 of BS 7671 covers fire detection and alarm circuits.
Regulation 560.7.1 states that these safety services must be
independent of other circuits.
This is also a requirement of BS 5839 Fire Detection and Fire
Alarm Systems for Buildings. Clause 25.2 states that the mains
supply to the fire alarm system should be from the load side
of the main isolating device for the building and have its own
isolating protective device (such as a circuit-breaker).
The circuit should also be from a point in the electrical distribution
system that is close to the main isolating device for the building.
In addition, every protective device that can isolate the supply to
the fire alarm system, other than the main isolator for the building,
should be clearly labelled: “FIRE ALARM. DO NOT SWITCH
OFF” in a durable and fade resistant material.
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