28.1 Commentary

1. Electromagnetic Interference (EMI) Sources:

● EMI can come from mobile phones, radio transmitters, building equipment, lightning, and power transients.

● EMI issues can arise from close proximity of fire alarm cables to high-current, inductive power cables.

2. Factors Influencing EMI Susceptibility:

● Susceptibility of fire alarm equipment.

● Cable screening level.

● Separation distance between fire alarm cables and other service cables.

3. Cabling Recommendations:

● Cables in 26.2b) offer some screening, but proper installation practices are crucial.

● Avoid running fire alarm cables in close proximity (more than 35m) to high-current power cables.

4. Reducing EMI:

● Metal partitions (e.g., compartmented trunking) can reduce EMI.

● Aim to maintain separation between fire alarm cables and other service cables, especially in addressable and networked systems.

● Cross fire alarm cables with other service cables at right angles to minimize EMI.

5. Manufacturer Guidance:

● Follow specific recommendations from the fire alarm equipment manufacturer regarding separation and installation to mitigate EMI.

28.2 Recommendations

The following recommendations are applicable.

1. Component Standards: Ensure every system component meets relevant product standards for electromagnetic capability.

2. Cable Segregation: Follow guidelines for cable segregation as specified in sections 26.2l) and 26.2n).

3. Installation Workmanship: Adhere to quality standards for terminations and continuity of screens; ensure effective screen terminations.

4. Cable Specifications: Use manufacturer-specified cables; any deviations require prior agreement and should be documented.

5. Earthing: Proper earthing of equipment is crucial for both EMC performance and electrical safety; follow recommendations in Clause 29, 37.2f), and Figure 18.

6. Exposure Minimization: Minimize the exposure of cores outside the screen during installation.

7. Screen Earths: Follow manufacturer instructions on multiple screen earths if the system is sensitive to these.

8. Screen Continuity: Ensure screen continuity throughout the entire circuit as needed.

9. Cable Crossing: Cross fire detection and fire alarm cables with potential interference-causing cables at right angles to minimize EMI.

28 Electromagnetic compatibility