A self-powered audible device is equipped with an internal source of energy to power the bell. In the event of the main power failure, it can still activate via a secondary power source. In most bells, a backup battery is used. The modern bell boxes comply with the British standard BS50131 and use rechargeable Ni-Cd batteries which are kept charged by the control unit. A self-powered audible device needs to comply with Annex C of PD 6662: 2004 and with all the other provisions of prEN 50131-1: 2004 relevant to WDs.
The code of practice (Sub-clause 8.1.4 of prEN 50131-1:2004) also emphasis that means shall be provided to recognise a fault condition in the alternative power source.
A self-powered audible device is equipped with an internal source of energy to power the bell. In the event of the main power failure, it can still activate via a secondary power source. In most bells, a backup battery is used. The modern bell boxes comply with the British standard BS50131 and use rechargeable Ni-Cd batteries which are kept charged by the control unit. A self-powered audible device needs to comply with Annex C of PD 6662: 2004 and with all the other provisions of prEN 50131-1: 2004 relevant to WDs. The code of practice (Sub-clause 8.1.4 of prEN 50131-1:2004) also emphasis that means shall be provided to recognise a fault condition in the alternative power source.