26.1 Commentary

1. Interconnections:

● Cables and wiring are typically used but can be replaced by radio or fiber optics.

● Fiber optic connections need to match the integrity and reliability of recommended cables.

2. Critical Signal Paths:

● Essential cables must function during a fire, especially those linking control equipment to manual call points, detectors, alarm devices, and routing equipment.

● Critical signal paths should use fire-resistant cables and proper support to prevent strain and failure.

3. Mains Supply:

● Mains circuits need fire protection despite the presence of a standby supply.

4. Fire Alarm Devices:

● Should not rely on continued signals from detectors or call points after activation.

● Large buildings may need ongoing indication capabilities during a fire.

5. Fire Resistance Levels:

● Two levels: "standard" and "enhanced," based on BS 7629-1 requirements.

● Enhanced fire resistance is recommended for critical applications like high-rise buildings and large premises.

6. Mechanical and Electromagnetic Protection:

● Use robust cables, careful routing, and protection against mechanical damage.

● Monitor circuits to quickly identify and repair faults.

● Segregate fire alarm circuits from other circuits to avoid electromagnetic interference and damage.

7. Cable Characteristics:

● Ensure electrical characteristics, such as current capacity and voltage drop, are suitable.

● Avoid electromagnetic interference and ensure compatibility with data transmission needs.

8. Identification and Segregation:

● Preferably use red cables for fire alarm circuits for easy identification and to prevent accidental interference.

26.2 Recommendations

The following recommendations are applicable.

1. Electrical Characteristics:

● Suitable voltage drop, current capacity, impedance, and data transmission ability.

2. Fire-Resistant Cables:

● Critical signal paths and low voltage mains supply must use:

a) Mineral insulated copper sheathed cables (BS EN 60702-1, 2).

b) Cables meeting BS 7629-1 or BS 7846 with standard/enhanced fire resistance.

c) Cables rated 300/500V with similar safety levels.

3. Resistance to Fire:

● Use standard fire-resisting cables for most systems.

● Enhanced fire-resisting cables for:

a) Buildings with phased evacuation (4+ phases).

b) Unsprinklered buildings over 30m high.

c) Large, unsprinklered premises where people might remain during a fire.

d) As determined by fire risk assessment.

4. Fire Resistance Duration:

● Standard: 30 minutes (BS EN 50200, Annex D, E).

● Enhanced: 120 minutes (BS EN 50200, Annex D, BS 8434-2).

5. Cable Support:

● Non-combustible supports maintaining circuit integrity.

● Avoid plastic clips/ties; use materials enduring similar fire conditions as cables.

6. Installation:

● Minimize external joints; use junction boxes labeled "FIRE ALARM".

● Joint materials should withstand fire temperatures.

7. Mechanical Protection:

● Use MI copper sheathed or steel wire armored cables in harsh conditions.

● Provide additional protection (e.g., trays, conduits) in vulnerable areas (<2m above floor).

8. Segregation:

● Fire alarm cables should not share conduits with other services.

● Use separate compartments in trunking for fire alarm cables.

9. Conductor Size:

● Minimum cross-sectional area: 1 mm².

10. Color Coding:

● Use a common color distinct from general electrical services for easy identification.

11. Electromagnetic Interference:

● Follow manufacturer recommendations for separation from other service cables.

12. Multi core Cables:

● Use solely for fire alarm circuits; no shared conductors with other systems.

13. Power Separation:

● Segregate cables carrying power >ELV from ELV circuits; avoid shared entries and ensure internal separation within equipment.

NOTE 1 In a building with a networked system (see Clause 24), individual, self-contained fire detection and fire alarm systems sometimes serve parts of the building that are evacuated in less than four phases, even though the entire building is evacuated in four or more phases. In such cases, cables of enhanced fire resistance need not be used for these systems, but there might be a need to use cables of enhanced fire resistance for the network [see Figure 17a) and Figure 17b)].

NOTE 2 Height of a building is taken as the height from the lowest level of the ground around the perimeter of the building to the floor level of the top storey.

NOTE 3 If the single range of buildings shown in Figure 17c) were served by a networked system, and each of the independently evacuated sections shown were served by individual, self-contained fire detection and fire alarm systems, cables of enhanced fire resistance would not be necessary except, in the case of the network cables, if required to satisfy the recommendations of Clause 24.

NOTE 4 Effects of fire include discharge of water from extinguishing systems or equipment and impact by falling objects.

NOTE 5 A cable system comprises the cables, the means by which cables are secured and the means by which cables are jointed.

NOTE 6 For the purpose of 26.2c), a building is regarded as sprinklered only if an automatic sprinkler installation conforming to BS EN 12845 is provided throughout the building, except that the requirements of BS EN 12845 for life safety installations need not be applied.

NOTE 7 In some fire engineering solutions used for complex buildings, a reduction in the normal level of other fire protection measures throughout the building might be acceptable to an enforcing authority provided an automatic fire detection system is installed. In such cases, an enforcing authority might or might not, as part of the fire engineering solution, require cables of enhanced fire resistance, and early consultation with the authorities responsible for enforcing fire safety legislation is strongly recommended (see Clause 6).

NOTE 8 This corresponds to class PH 30 as detailed in BS EN 50200:2015, Annex D.

NOTE 9 This corresponds to class PH 120 as detailed in BS EN 50200:2015, Annex D.

NOTE 10 In effect, this recommendation precludes the use of plastic cable clips, cable ties or trunking, where these products are the means of cable support.

NOTE 11 Experience has shown that collapse of cables, supported only by plastic cable trunking, can create a serious hazard for firefighters, who could become entangled in the cables.

NOTE 12 Examples of suitable terminals include metal components mounted in ceramic terminal blocks.

NOTE 13 At the time of drafting this standard, no definitive guidance can be given on the means for ensuring that the entire cable system, as opposed to the cable itself, can provide adequate resistance to the effects of fire. The manufacturer’s recommendations need to be followed.

NOTE 14 This recommendation does not preclude the multiplexing of signals of other systems with those of the fire detection and fire alarm system. Guidance on such integrated systems is given in DD CLC/TS 50398.

NOTE 15 The color red is preferred.

Figure 17 — Example of a networked fire alarm system

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Figure 17 — Example of a networked fire alarm system (Continued

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26 Cables, wiring and other interconnections