BS 8519 2020

If you are responsible for specifying, inspecting or regulating fire resistant cables for large or complex buildings then you need to be aware that the standard BS 8519 has been fully revised. Martin Boorman from Prysmian outlines some of the major changes to the guidance on selection and installation of fire-resistant power and control cables. Buildings are getting bigger. As their size continues to increase so too does the complexity of the active fire protection systems, such as sprinkler pumps and smoke control devices, needed to enable those inside a building to escape and to protect emergency and fire personnel.

 

For these systems to continue to operate in a fire their electrical power and control cables must be able to maintain circuit integrity. Fortunately, the recently published British Standard 8519:2020 explains how such systems should be selected and installed. The standard identifies electrical loads defined as life safety and fire-fighting and gives specific recommendations for electrical system design for fire survival times.  The revised standard BS8519:2020 came into effect on 30 June 2020. It replaces BS8519:2010, which has been withdrawn. So, what's new about BS8519:2020? The short answer is quite a lot....

 

BS 8519:2020 is a full revision of BS 8519 and adds much new information to aid the designer and installer.  However, the essential principles of BS 8519 remain unchanged (e.g. dual independent electrical supplies served by fire resistant cables). The primacy of BS 5839-1, BS 5839-8, BS 5839-9 and BS 5266-1 for installations that they cover remains and BS 8519:2020 does not give recommendations for such installations.

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The scope of BS 8519 has been extended from life safety and fire-fighting applications to include systems which need to maintain their circuit integrity during a fire because they support critical business continuity, property protection or environmental protection functions.

The references have been updated and expanded.

The references have been updated and expanded.  The definition of “fire-resistant cable” remains unchanged.

The electrical system is now required to be “verified” by a skilled person.

The survival times are unchanged but for clarity the circuits are now classified as circuit category 1, 2 or 3, to align with cable categories.  The application list of Table 1 is now part of this clause.  The Table has been updated and the requirements for “Sub-main power distribution” corrected.

The clause has been extensively rewritten to improve clarity although the basic requirement for fire-resistant/protected primary and secondary supplies is unchanged.  Information on UPS supplies is included, based on the recommendations of BS 9991 for residential buildings.  A new Annex A is referenced for further guidance on the selection and specification of UPS/battery inverter systems.  The prime recommendation of BS 8519 for the secondary power supply remains an automatically started standby generator.  Additional recommendations for life safety generators and roof-mounted generator are included.

Figure 1 “Example of dual supply has been redrawn for greater clarity.  Figure 2 from the 2010 edition is no longer included as systems using a standby primary utility supply are no longer considered to be sufficiently independent and resilient.

The clause has been rewritten to improve clarity.  Standard HV cables installed within cable protective systems are now required to conform to BS 7835.  The requirement for the degree of thermal protection is now clarified.  A requirement for LV power supplies to be installed on a dedicated support system is introduced.

The clause is updated to include a fire-resistant classification for the enclosure.

The clause is expanded and rewritten for clarity and to introduce further recommendations.

The clause is redrafted for clarity.

Some updating and minor rewording is introduced but the cable requirements remain unchanged except that Category 3 control cables now have to additionally meet the 120 min survival time when tested in accordance with BS 8434-2.  The Category of cable to be used for particular applications continues to be given in Table 1.

It should be noted that a requirement for cables to meet a constructional standard (BS 7835, BS 7629-1, BS 7846 or BS EN 60702-1) is now included via NOTE 1 and NOTE 2.

It should also be noted that the use of a Category 3 control cable as a small power cable is recognised provided that the cable is mechanically protected (e.g. armoured).  Such use of an unarmoured cable would be subject to the provision of additional mechanical protection.

This clause has been completely re-written and much additional detail provided to cover the use of such systems as a means of protecting non fire-resisting HV cables.  Note that the use of fire-resisting HV cables is not recognised by BS 8519.  The protective system should be a four-sided factory-built assembly.

Many further detailed recommendations are given regarding the design and selection of such systems.  New recommendations for internal and external fire stopping to maintain the switchroom fire compartmentation are included.  A new Annex C is included to give further information on the testing of such systems.

The clause has been rewritten for improved clarity and specific recommendations added.  Any guidance given in applicable Wiring Regulations or specific advice from the cable manufacturer should be taken into account.  A default position of an increase of the conductor size by two sizes (compared to that selected for normal operation) is recommended in cases where guidance is absent and detailed calculations are not possible.  The informative guidance previously given in Annex C and Annex D is retained in new Annex E and Annex G.

The clause has been revised and minimum conductor size for supplementary CPCs has been removed.

The clause has been subject to updating and detail improvement although general principles remain unchanged.  Note the new guidance in i) covering installation in vertical risers.  Greater weight is now given to following the installation practices recommended by material suppliers and equipment manufacturers in order to prevent support system collapse under fire conditions.

The clause is rewritten to include some recommendations previously placed in clause 15.  Separate support systems for fire-resistant and non-fire-resistant cables are recommended.

The clause has been completely rewritten and a new test protocol suitable for junction boxes or cable joints included.

A new clause has been added to recognise such systems which are tested in accordance with BS 8602.

This clause is essentially unchanged.

This new clause includes matter previously covered in clauses 17 and 18 together with much new guidance / recommendations concerning specific areas of application.

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This new informative annex covers the selection and specification of UPS/battery inverter systems as mentioned in clause 6.

This informative annex on typical HV (previously designated MV) circuit in a building is unchanged from the previous Annex A.

This new informative annex concerns performance criteria and testing of cable protective systems for HV circuits and supports clause 12.

This normative annex on testing small category 3 cables is technically unchanged from the previous Annex B.

This normative annex concerning cross-sectional area of drop rods is a revision of the previous Annex E.  The maximum allowable stress of steel drop rods has been substantially lowered for each fire duration.

This informative annex on voltage drop calculations for cable in a fire is technically unchanged from the previous Annex C and supports clause 13.

This informative annex on cable under fire and fault conditions is technically unchanged from the previous Annex D and supports clause 13.

This new informative annex concerning cable protective systems to BS EN 1366-11 gives a justification as to why systems complying with this standard (developed by CEN TC 127 in support of CPR) are not considered suitable to meet BS 8519 requirements.

This new informative annex on mechanical loading of drop rods supports Annex E.

This new informative annex introduces a format for reporting variation from the recommendations of BS 8519:2020 to be used in circumstances where the recommendations would be difficult or impossible to implement.  It is based on a similar principle given in BS 5839-1.

This annex has been deleted as the content is no longer considered appropriate for the standard.  It is partly replaced by clause 20.