Ask the experts/Technical
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We continue with our series of answers to some of the more frequently asked questions put to our Technical Helpline. QUESTION
ANSWER
Is Regulation 521.11.201, regarding the fire resistance of supports for cables in escape routes, applicable to supports for communication system cables, such as door entry and internet?
Yes. The requirements of BS 7671 apply to the fixed wiring of circuits supplied at nominal voltages up to and including 1000 V a.c. and 1500 V d.c., which therefore includes systems for information and communication (Regulation 110.1.2 refers). It should be noted that certain systems, such as telecommunications systems to BS 6701, may contain other requirements which supplement BS 7671 (Regulation 110.1.3 refers).
QUESTION
ANSWER
Where I observe during periodic inspection communication system cables installed in non-metallic trunking, surface-mounted at high level in an escape route what (if any), classification code should I record on an Electrical Installation Condition Report?
It should be remembered that Regulation 521.11.201 has been introduced by Amendment 3 to BS 7671 to minimise supported wiring systems, prematurely in the event of fire, falling and/or dangling, and therefore hindering persons escaping from a building and firefighters carrying out search and rescue activities. Regardless of the type of cable, Regulation 521.11.201 requires supports for wiring systems (including cables) to have sufficient resistance to the products of combustion from fire to minimise the risk of the support prematurely collapsing. This requirement effectively excludes the sole use of non-metallic supports (such as plastic cable clips and cable trunking). Therefore, you should attribute, as a minimum, a classification code C3 to your observation. Further information on fire incidents involving non-metallic supports can be found in Connections 179.
QUESTION
ANSWER
Relating to the question above, ‘as a minimum classification code C3’ under what circumstances (if any) would you attribute a classification code C2?
Where an inspection reveals wiring systems in escape routes supported solely by non-metallic supports the inspector must assess the risk of the wiring system and associated cables, at times of fire, becoming a hindrance to persons escaping from a building and firefighters carrying out search and rescue activities, due to premature collapse of the support. Consider the following two examples relating to the use of non-metallic trunking, and the degree of hindrance from cables falling and/or dangling at times of fire: • For a corridor 1 m in width, 3 m in height and forming part of an escape route; if trunking was surface-mounted on the ceiling to span the width of the corridor (1 m distance), should the trunking collapse or lid fail, the contained cables would have support from both walls and hindrance would be minimal, and a classification code C3 would probably be appropriate. • If the trunking was surface-mounted on the wall along the length of the same corridor, for every increasing metre length of corridor the potential for cables becoming a hindrance increases. Where the inspector judges that, due to the length of trunking and cable, the potential for hindrance is high, a classification code C2 would probably be more appropriate leading to an installation being deemed to be unsatisfactory.
Connections Summer 2015
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