24.1 Commentary

1. System Configuration:

● In networked systems, functions are distributed among remote "sub-panels" interconnected by a network, rather than centralized in one location.

● Sub-panels may act as data gathering points or fully functional control and indicating panels.

2. Installation Circumstances:

● Used in large systems beyond a single CIE’s capacity.

● Useful for centralized monitoring/control across multiple buildings on the same site.

3. Network Resilience:

● Ring/Loop Networks: More resilient to communication failures.

● Radial Networks: Less resilient compared to ring/loop.

● Peer-to-Peer Networks: Less vulnerable than central processor networks.

4. Impact of Communication Failures:

● Stand-Alone Panels: If panels operate independently, communication failures are less critical.

● Critical Systems: If the network is integral to primary functions (e.g., alarming, summoning rescue services), it must be monitored and protected as a critical signal path.

5. Requirements:

● The network should have the same integrity, reliability, and availability as a single system.

● It must be monitored for faults, use suitable cabling, and ensure a response to manual call points within 10 seconds (with a 3-second response within the alarm zone of origin).

● The communications link should be treated as a critical signal path if it is essential for primary alarm functions.

24.2 Recommendations

The following recommendations are applicable.

1. Sub-Panels:

● Non-Indicating Sub-Panels: No indication facilities needed; should be accessible for maintenance. Audible warnings may be suppressed.

2. Communications Link:

● Monitoring: Required for wired networks (12.2.1) and radio networks (BS EN 54-25:2008, 4.2.6).

● Fault Handling: Should not affect any sub-panel operation.

● Critical Signal Path: If part of critical path, cable installation must conform to 26.2, with specific conditions for using fire-resisting cables:

a) Network configured as a loop.

b) Diverse routing of circuits.

c) No loss of communication due to single circuit failure.

3. Alarm Signal Timing:

● Manual Call Point to Evacuate Signal: Should comply with 20.2b), with no more than 10 seconds delay for zones beyond the manual call point.

4. Ancillary Circuit Cable Installation:

● Must conform to 26.2 for ELV supply from an external power supply unit.

NOTE Sub clause 26.2 recommends fire resistance only for cables that comprise parts of the critical signal paths and for low voltage (LV) mains supply cables.

24 Networked systems