12.1 Commentary

The standard aims for highly reliable fire alarm systems by minimizing faults and ensuring fast repair. While redundancy in wiring isn't usually necessary, fire alarm circuits are an exception. Here's why:

● Fire damage during evacuation shouldn't silence the alarm and mislead occupants.

● A single fault shouldn't disable all alarms.

Approaches for Redundancy:

● Large Buildings: Multiple circuits serving different areas provide backup in case one fails.

● Smaller Buildings: A separate circuit with at least one alarm ensures sound even if the main circuit fails.

● Large Public Spaces: Due to high life risk, additional circuits are recommended. Voice alarm systems with extra loudspeaker circuits are advised for these spaces

Key Points:

● Faulty circuits should trigger a fault signal at the control panel.

● Multicore cables are not ideal for fire alarm circuits because a single fault could disable multiple circuits.(see 3.14)

12.2 Recommendations

12.2.1 Fault monitoring

The following recommendations are applicable.

Here's a condensed summary of the requirements for fault indications and system integrity according to BS 5839:

a) Fault Indications for Circuits and Devices:

● The Control and Indicating Equipment (CIE) must indicate faults within 100 seconds for:

1. Short or open circuits in circuits serving manual call points or fire detectors.

2. Removal of detachable manual call points or fire detectors.

3. Short or open circuits in circuits serving fire alarm devices.

4. Wiring faults between separate power supplies and equipment.

5. Earth faults affecting system performance.

6. Fuse ruptures or protective device operations affecting system performance.

7. Wiring faults between separate control equipment.

8. Wiring faults between main and repeat control equipment.

9. Wiring faults affecting transmission of alarm signals to an ARC.

10. Removal of detachable fire alarm devices.

b) Fault Indications for Power Supply Failures:

● Fault indications should be given within specified times for:

1. Failure of main power supply (within 30 minutes).

2. Failure of standby power supply (within 15 minutes).

3. Failure of battery charger (within 30 minutes).

4. Reduction of battery voltage below specified level (within 30 minutes).

c) Visual Indications during Fire Alarm Condition:

● Visual indications of faults related to fire alarm devices and transmission should continue during a fire alarm condition, while other fault indications may be suppressed.

NOTE The recommendations of a), b) and c) can be satisfied by the use of CIE and power supply equipment conforming to BS EN 54-2 and BS EN 54-4, respectively, provided the system installation complies with the recommendations of the manufacturer, on which conformity with BS EN 54-2 and BS EN 54-4 might be reliant.

d) Standby Power Supply:

● In systems with parallel-connected batteries for standby power, a fault indication should occur if any battery is disconnected within 15 minutes.

e) Voice Alarm System Integration:

● Fault indications should occur within 100 seconds for any disconnection or short circuit between the fire detection system and a separate voice alarm system or fire warning system for people who are Deaf and hard of hearing.

f) Actuation of Other Systems:

● If the system activates other fire protection systems or safety facilities, monitoring connections should comply with BS 7273 or relevant codes of practice.

g) Tactile Fire Alarm Devices:

● Systems with tactile fire alarm devices must indicate failure to receive monitoring signals correctly, per Annex C.

These requirements ensure that faults in the fire detection and alarm system are promptly identified and indicated, maintaining system integrity and reliability.

12.2.2 System integrity

The following recommendations are applicable.

a) Fault Isolation for Circuits:

● A fault on one circuit containing manual call points, fire detectors, or fire alarm devices should not affect any other circuit.

b) Automatic Fire Detector Circuit Faults:

● A single short circuit or open circuit fault on an automatic fire detector circuit should:

i) Not disable protection in an area larger than 2,000 m².

ii) Not affect more than one floor of the building.

iii) Impact a maximum of five devices (automatic detection, manual call points, sounders, or a combination) on the floor above and below that floor.

c) Manual Call Point or Fire Detector Circuit Faults:

● Two simultaneous faults on a manual call point or fire detector circuit should not:

i) Disable protection in an area larger than 10,000 m².

NOTE 1 The areas quoted in b) and c) are relatively arbitrary; in the case of b), the recommendation is based on custom and practice in non-addressable fire detection and fire alarm systems over many years. Engineering judgment might determine that, in a given system, minor increases in the areas quoted do not significantly impede the system integrity, but this ought then to be regarded as a variation from the recommendations of this standard.

d) Software Controlled CIE with Many Connections:

● Software controlled CIE (Control and Indicating Equipment) handling more than 512 detectors and/or manual call points should adhere to manufacturer instructions on achieving conformity with BS EN 54-2.

e) Detachable Detectors for Maintenance:

Operation Independence: Detectors designed for detachability from their bases for routine maintenance:

Removal of any detector(s) from the circuit should not affect the operation of any manual call point, regardless of whether locking devices secure detectors within their bases.

NOTE 2 This recommendation applies even if all fire detectors in the system are removed from the circuit.

Malicious Removal Considerations:

During the design stage, consider the potential for malicious removal of detectors.
If malicious removal is anticipated, use detectors that require a special tool or technique for removal.

NOTE 3 A special tool in this context is a tool not likely to be carried by a member of the general public. Slot-headed screws would not be acceptable, since various articles can be used as screwdrivers.

f) Deliberate Disablement Facilities:

Facilities for deliberate disablement of manual call point or detector circuits should:
Enable disabling of protection within one zone without affecting other zones.
Not hinder building evacuation via an evacuation control on or near the CIE.

g) Impact of Removal on Alarm Devices:

● Removal of any manual call point or detector from its circuit should not affect the ability of any fire alarm device to respond to an alarm signal, except for devices combined at a single fixing position.

h) Secure Removal of Fire Alarm Devices:

● Fire alarm devices should only be removable using a special tool.

i) Fault Tolerance for Fire Alarm Sounders:

In case of a single open circuit or short circuit fault on any circuit serving fire alarm sounders:
At least one fire alarm sounder, typically near the CIE, should still sound correctly if a fire alarm condition arises anywhere in the building.
This sounder should emit an identical sound to general fire alarm sounders in the building.

NOTE 4 It is possible to comply with this recommendation by at least the following two arrangements, although other arrangements are not precluded:

• wiring all fire alarm sounders within the building on a single sounder circuit, with the additional provision of a second, independent sounder circuit, to which only a single sounder, located in the vicinity of the CIE is connected [see Figure 1a)];

• wiring all fire alarm sounders on a ring circuit capable of transmitting signals in either direction; the first (or last) three devices on the circuit would then comprise a short circuit isolator, capable of isolating the circuit in the event of detection of a short circuit, a sounder and a further short circuit isolator [see Figure 1b)].

NOTE 5 The sounder that continues to operate normally comprises one of the general alarm sounders in the area in which the CIE is housed. In a building without phased evacuation, the alarm sounder gives an “Evacuate” signal until silenced. In a building with multi phase evacuation, the sounder may give an “Evacuate” signal or “Alert” signal until silenced, according to the location(s) from which the fire alarm signal originates and the phase of the evacuation at the time in question.

j) Sounder Circuits in Buildings for Public Use:

Requirement for Uncompartmented Public Spaces:

In buildings designed for large numbers of the general public (e.g., transport terminals, shopping centers), provide at least two sounder circuits in each uncompartmented public space if:
The area exceeds 4,000 m², or
The space is designed to accommodate more than 500 members of the public.

Implementation Options:

Ensure compliance by: i. Distribution of Sounder Circuits:
Use at least two sounder circuits evenly distributed and interleaved so adjacent sounders operate on different circuits. ii. Protected Loop Circuit:
Utilize a protected loop circuit where no more than 50% of sounders in the area would be lost in case of a single open or short circuit fault.

NOTE 6 The figures of 4 000 m2 and 500 members of the public are arbitrary, but are the criteria for duplication of loudspeaker circuits of voice alarm systems conforming to BS 5839-8. Engineering judgment might determine that, in a given system, a single sounder circuit can be used to protect a public space that slightly exceeds these criteria without undue increase in risk to occupants. This would then be regarded as a variation from the recommendations of this standard.

NOTE 7 It is not intended that this recommendation would be applied to small cellular spaces or non-public areas of the buildings in question.

k) Where two or more sounder circuits are required to meet recommendations, they should not share a common cable sheath to prevent simultaneous failure. Using separate cables ensures each circuit remains independently protected, reducing the risk of complete circuit loss.

NOTE 8 This recommendation does not apply to those sounder circuits that need not be independent to satisfy the recommendations of this standard (e.g. that are provided purely as a result of electrical engineering considerations).

l) If the Control and Indicating Equipment (CIE) receives power from separate power supply equipment in another enclosure, cables connecting them should be duplicated to prevent complete power loss due to a single fault. These duplicate cables should ideally be separated by at least 300 mm for practicality. Additionally, any cables between the separate enclosure and the CIE must be adequately protected against overcurrent according to BS 7671 regulations.

NOTE 9 Where the enclosure is located immediately adjacent to, and in contact with, the CIE, such that cables run directly between the enclosure and the CIE, the enclosure need not be regarded as separate from the CIE; the recommendations of 12.2.2l) do not then apply.

Figure 1 — Sounder circuits

Figure 1 — Sounder circuits (Continued)

12 Monitoring, integrity and reliability of circuits external to control equipment