Answers are based on the requirements of BS 5839-6: 2004
Is it permitted for the power to a fire alarm and detection system in a dwelling to be provided from a regularly used local lighting circuit?
For a Grade D system, the answer is yes. A regularly used local lighting circuit of the dwelling may be used for the power supply (clause 15.5(a)ii of BS 5839-6: 2004 refers).
For systems of Grades A, B, C and E, the answer is no. All of these systems require a power supply from an independent circuit at the dwelling’s main distribution board. No other electrical equipment should be connected to this circuit.
How should an interlink (or signal) conductor used for interconnecting smoke or heat alarms in a dwelling be identified?
Clause 16.5 (c) of BS 5839-6: 2004 states, with regard to the wiring of Grade D and E systems, that ‘conductors used for interconnection of smoke/heat alarms should be readily distinguishable from those supplying power (e.g. by colour coding)’.
The object of this recommendation of BS 5839-6: 2004 is to avoid the possibility of confusion between the interlink conductor, which generally operates at extra-low voltage, and the conductors providing the a.c. power supply. Therefore, the interlink conductor should be identifiable not by the colour brown (which is used for the phase conductor of the 230 V a.c. power supply), but by some other colour appropriate to a phase conductor, which must be in accordance with the requirements of BS 7671.
Where the harmonized cable colour scheme is used, the colour used to identify the phase conductor of a control circuit or extra-low voltage circuit must (excluding brown) be black, red, orange, yellow, violet, grey, white, pink or turquoise (Table 51 of BS 7671: 2001, as amended, refers).
The diagram opposite shows a simple method of meeting this requirement where a three-core-and-earth cable having core colours of brown, black and grey is used as the phase, neutral and interlink conductors interconnecting heat or smoke alarms.
What requirements for segregation (or separation) apply to the wiring of a fire alarm and detection system in a dwelling?
To avoid electromagnetic interference with fire alarm signals from the wiring of other services or other voltages, any recommendations of the fire alarm system manufacturer with regard to segregation or separation of fire alarm wiring should be followed. (Clause 26.2 (l) of BS 5839-1: 2002 refers for Grade A and B systems, and clause 22.2 of BS 5839-6: 2004 refers for Grade C systems.)
For a Grade A system, to avoid the risk of mechanical damage to the fire alarm cables, they should not be installed within the same conduit as the cables of other services. Where the fire alarm cables share common trunking, a compartment of the trunking, separated from other compartments by a strong, rigid and continuous partition, should be reserved solely for fire alarm cables. (Clause 26.2(k) of BS 5839-1: 2002 refers.)
For Grade A and B systems, the mains supply cable to any control, indicating or power supply equipment should not enter the equipment through the same cable entry as cables carrying extra-low voltage. Within the equipment, low voltage and extra-low voltage cables should be kept separate to the extent practicable. (Clause 26.2(n) of BS 5839-1: 2002 refers.)
In addition to the above, for protection against electric shock, the requirements of Regulation Group 528-01 of BS 7671 must be complied with. In particular, a band I circuit (e.g. extra-low voltage) must not be contained in the same wiring system as a band II circuit (e.g. 230 V) unless one of the methods in indents (i) to (vi) of Regulation 528-01-02 is adopted, such as every cable being insulated to the highest voltage present.
It is necessary to measure the sound pressure levels provided by a fire alarm and detection system in a dwelling?
For a Grade A system, measurement of sound pressure levels is necessary. Clause 23.2(a) of BS 5839-6: 2004 recommends testing, commissioning and certification of the system in accordance with Sections 4 and 5 of BS 5839-1: 2002.
For a Grade B system, no recommendation to measure sound pressure levels is made in BS 5839-6: 2004. However, the sounders of a Grade B system are separate from the fire detectors, and there may therefore be fewer sounders than detectors. Consequently, measurement of sound pressure levels may be necessary in practice, in order to verify that the recommended values are provided.
For Grade B, C, D and E systems, no recommendation to measure sound pressure levels in a dwelling is made in BS 5839-6: 2004. Compliance with recommended sound pressure levels may result from the fact that the sounders of these grades of system are integral to the smoke alarms and heat alarms, which are usually fitted in, at least, the circulation areas, such as hallways and landings. For example, if a smoke alarm complying with BS 5446-1 is installed outside a bedroom and not more than 3 m from the doorway, a sound pressure level of at least 85 dB(A) will be provided at that doorway (with the door open), as recommended in certain circumstances by clause 13.2 of BS 5839-6: 20041.
1A higher sound pressure level might be necessary if occupants are hard of hearing or if bedroom doors attenuate sound by significantly more than 20 dB. Also, for bedrooms in some houses in multiple occupation where ambient noise levels and other factors justify it, a sound pressure level of 75 dB(A) at the bedhead may be needed.