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FP200 Gold and fire resistant cables from Prysmian Cables UK

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FP200 Gold and fire resistant cables from Prysmian Cables UK

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FP200 Gold and fire resistant cables from Prysmian Cables UK

Requirements for Fire Resistant Cables
Posted: 25/01/07 16:37:09

Requirements for Fire Resistant Cables

Terry Journeaux examines fire safety issues on terms of electric cable, particularly in respect of the updated edition of the Technical Handbook and the revised Approved Document B on fire safety.

With the updated edition of the Technical Handbook coming into effect in May 2007 to provide practical guidance with respect to the Building Regulations for Scotland, and the revised Approved Document B Fire Safety coming into effect in April 2007 to provide practical guidance with respect to the Building Regulations for England and Wales, it is an opportune time to consider the changes made to both sets of guidance and the differences between them with respect to the use of fire resistant cables.

Direct references to cables are limited and both guidance documents make just one direct reference to the use of fire resisting cables but both contain important indirect references through references to British standards that do contain specific requirements for the fire resistant properties of the cables to be used.

The references in Section 2 Fire of the updated Technical Handbook are essentially unchanged from the previous version whereas some significant changes have been introduced in the revised Approved Document B (ADB). Both documents are now split, between domestic and non-domestic in the Technical Handbook and between dwellinghouses and buildings other than dwellinghouses in the ADB.

Concentrating on the non-domestic area, both guidance documents refer directly or indirectly to the use of fire resistant cables in:

  • escape and emergency lighting
  • fire detection and alarm circuits
  • other protected circuits, including smoke and heat exhaust ventilation systems

Escape lighting

The Regulations for Scotland require that “Every building must be designed and constructed in such a way that in the event of an outbreak of fire within the building, illumination is provided to assist in escape.” The Technical Handbook states that an escape route should have artificial lighting supplied by a protected circuit (2.10.1), further defines a protected circuit as one “…originating at the main incoming switch or distribution board, the conductors of which are protected against fire”, and additionally emergency lighting should be installed in buildings or parts of buildings considered to be at higher risk (2.10.3). Such lighting should comply with BS5266- 1:1999 except for places of entertainment where CP 1007:1955 applies.

Where it is decided to install a protected circuit to an existing lighting system, in the absence of any specific guidance, it would be logical to assume a similar performance requirement for the cables as given in BS5266-1:1999 which requires either mineral insulated cables to BS6207-1 or cables complying with BS6387 of at least category B unless additional protection is applied. A useful alternative method recognised by BS5266-1 is the use of fire resistant conduit wires of the FP100 type enclosed in steel conduit where these have been subjected to the BS6387 tests.

ADB follows a similar approach and refers to BS5266-1 but the new 2005 edition which replaced BS5266-1:1999 and CP1007:1955 when they were withdrawn in late 2005. This includes updated cable requirements against BS EN50200 (PH60). ADB also defines requirements for protected circuits, historically BS6387 category CWZ but updated to refer to BS EN50200.

Whilst it is assumed that the updating of British Standard references will be considered in due course for the Technical Handbook, good practice in the meantime would suggest cables that meet both the BS5266-1:1999 and BS5266-1:2005 requirements should be specified.

Fire alarm communication

The regulations for Scotland require that “Every building must be designed and constructed in such a way that in the event of an outbreak of fire within the building, the occupants are alerted to the outbreak of fire”. The Technical Handbook recommends that automatic fire detection in accordance with BS5839-1:2002 is installed in many types of building (2.11.0). Additional guidance for specific types of building (residential care, hospitals, shopping centres) is given in the annexes.

The new cable requirements introduced in this BS have been well documented and a range of products are available to satisfy both the “standard” and “enhanced” application areas. It is important to note that a major change in the 2002 edition of BS5839-1 was to require the use of fire resistant cables in both detection and alarm circuits.

Interestingly, the Technical Handbook makes specific reference to the consideration of voice alarm systems to BS5839-8:1998 for buildings with vertically phased evacuation and shopping centres. It should be noted that currently the cable requirements of Part 8 differ from Part 1 in only requiring compliance with BS6387. In practice, the use of cables complying with both Parts has become the industry norm for such systems and this is likely to be reflected in the current revision of BS5839-8. In this area ADB takes a similar approach with reference to the same British Standards.

Other protected circuits

The Technical Handbook makes a further reference to the use of fire resistant cables in Annex 2.C “Additional guidance for enclosed shopping centres”, stating that a smoke and heat exhaust ventilation system (SHEVS) should be installed in centres and shops over a defined storey area. Any power source to elements of the system is required to be connected by mineral insulated cables or cables meeting BS6387 category A or cables protected to the same level.

This requirement, 3 hours circuit integrity under flame attack at 650C, is markedly different from ADB guidance which considers resistance to the effect of flame, shock and water to be important for such applications. AS previously stated, ADB historically required compliance with BS6387 categories CWZ for all protected circuits. The 2006 revision introduces more comprehensive guidance, particularly for large or complex buildings where systems may need to operate for an extended period during a fire, and directs the reader in particular to the further guidance on cable selection given in BS7346-6 “Components for smoke and heat control systems – Specifications for cable systems“

Whilst it is unlikely that cables meeting only BS6387 category A would be found on the UK market, cables meeting the more onerous BS6387 category CWZ are widely available and include armoured power types to BS7846. Cables meeting the more onerous test requirements of BS7346-6 are presently limited to heavy duty mineral insulated or FP600 interlocked steel tape armour types.

It is too early to say how the new ADB guidance will be applied in practice. Certainly in England and Wales there is a strong body of regulatory opinion that the more onerous requirements for the fire resistance of cables given in BS7346-6 are necessary to achieve the required level of safety in large and complex buildings where fire safety engineered solutions have to be used. The Technical Handbook also recognises under Alternative approaches (2.0.6) that “Fire safety engineering …… may be the only practical way to achieve a satisfactory level of fire safety in some large and complex buildings and in buildings containing multiple users such as airport terminals”. In such cases, the ADB guidance may prove valuable. Whilst debate continues and some further rationalisation of cable requirements between the Technical handbook and ADB guidance may be achieved, specifiers and users may remain assured that a selection of fire resistant cable products to meet both sets of guidance will remain available in the marketplace.

(First published in the May/Apr 2007 issue of WiredIn Magazine)


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