When a Grade D fire detection and alarm system to BS 5839-6: 2004 is protected by an RCD, should the RCD operate independently of any circuits supplying socket-outlets or portable equipment?
There are no particular requirements or limitations in BS 5839-6 concerning the use of RCDs with Grade D fire detection and alarm systems.
For Grade D systems, which comprise one or more mains-powered smoke alarms each with an integral standby power (such as typical domestic smoke alarm with battery), BS 5839-6 simply recommends that the mains supply to the smoke and/or heat alarms should take the form of either:
i) an independent circuit at the dwelling’s main distribution board, in which case no other electrical equipment should be connected to the circuit (other than a dedicated monitoring device installed to indicate failure of the mains supply to the smoke and/or heat alarms), or
ii) a separately electrically protected, regularly used local lighting circuit.
We recommend option ii) on the grounds that disconnection of the supply to the fire detection and alarm system will be more readily noticed. In our opinion ‘separately electrically protected’ does not preclude sharing an RCD with several other circuits where this is permitted by BS 7671.
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