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From the helpline 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 fi re 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

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), classifi cation code should I record on an Electrical Installation Condition Report?

QUESTION

Relating to the question above, ‘as a minimum classifi cation code C3’ under what circumstances (if any) would you attribute a classifi cation code C2? ANSWER

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 suff icient resistance to the products of combustion from fire to minimise the risk of the support prematurely collapsing. This requirement eff ectively 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.

ANSWER

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.

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QUESTION

Is Regulation 521.11.201 applicable to domestic premises?

QUESTION

I plan to make an addition to an existing installation; however, the distribution board houses protective devices to BS 3871, and I cannot fi nd any reference or operating characteristics for these devices in Chapter 41 and Appendix 3 of BS 7671. Is it still acceptable to rely on the use of such devices to provide fault protection? ANSWER

Yes. Regulation 521.11.201 applies to all buildings having a designated escape route. An escape route is defined in BS 7671 as ‘a path to follow for access to a safe area in the event of an emergency’, and in domestic premises this is typically the main route used for entering and exiting the premises, and would, in all likelihood, include (where applicable) the landing, stairs and hall.

ANSWER

Yes. BS 3871 was withdrawn in 1994 and consequently the operating characteristics of devices to that standard were removed from BS 7671 when it was reissued in 2001 (16th Edition Blue cover).

However, this does not mean that protective devices to BS 3871 cannot be relied on to provide fault protection. Indeed their limiting values of measured earth fault loop impedance for most current rating can be obtained from the inside cover of pads of NICEIC certificates and reports.

Furthermore, it is recommended that, due to the in-service age of such devices, a functional test, such as manual operation of the toggle switch, is carried out to verify the eff ectiveness of the mechanical operation.

The NICEIC and ELECSA publishing team

Sue Heybourne, technical illustrator Sue joined NICEIC in 2000 and previously worked for The Electrical Safety Council before moving to Certsure in 2013. She is responsible for producing and archiving all the illustrations for publications, articles and presentations, pocket guides and books. She also helps design all certifi cates.

Derek Cooney, technical author Derek is a time-served electrician who spent many years electrical contracting on domestic, commercial and industrial installations, before becoming a college lecturer. He joined NICEIC as a technical operations engineer in 2009.

Chris Long, technical engineer Chris is a gas professional responsible for providing a technical overview of all gas-related articles and publications. He lives in Hampshire with his family and outside of work is a motorbike nut.

John Clark, senior engineer John started out by serving a fi ve-year apprenticeship before spending some time installing plant in power stations. He then took a degree in electrical and electronic engineering before becoming a lecturer. He now works as senior engineer helping to develop the learning guides.

Tim Benstead, principal technical author Tim started his career as an apprentice electrician and worked in both contracting and maintenance prior to spending some 16 years as a lecturer. He began working for the Electrical Safety Council in 2006 as a senior engineer and has been part of the team responsible for the production of various NICEIC publications and certifi cates.

Mike Burling, senior engineer A former JIB technician, Mike had his own NICEIC-registered electrical contracting business, before taking on a role as a college tutor and NVQ assessor. He now works as a senior engineer responsible for overseeing the technical content of all technical publications and articles.