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Cable test BS 6387 category W has been removed, but it is expected that many manufacturers and specifiers will continue to request it.

In with the new… Greater certainty for specifiers

The fire cable industry has welcomed the introduction of the new British Standard BS 8592:2016 Electric cables; thermosetting insulated, non-armoured, fire-resistant single core non-sheathed cable of rated voltage 450/750V. This is first British standard for this type of cable, and was published on 31st March 2016.

The new single core cable standard ensures that these small-sized cables, commonly used for final circuit wiring of critical systems such as fire alarms and emergency lighting, now have a specification. These cables have been manufactured, distributed and widely used globally for many years but have not had a full specification, which has resulted in some variability between cable manufacturers. Now, the design and performance specifications are clearly defined, giving specifiers, designers and installers greater certainty that the cable should be fit for purpose.

Previously, cable manufacturers made reference to other similar standards and to test methods to support their design and manufacturing processes, however the new standard negates any grey areas. BS 8592:2016 will begin to be referenced in system design standards and will deter unsuitable alternatives from being used.

Put to the test

One of the major requirements to meet the new standard is to have ‘low emission of smoke and corrosive gases when affected by fire’. To describe a cable as Low Smoke Halogen Free (LSHF), it must generally pass two tests; a smoke cube test, which sets a maximum accumulated smoke density produced when burning the cable with a standard fire, and; a corrosive and acid gas test (related to the presence of halogens) where the cable materials are roasted in a tube furnace and must give off a maximum of 0.5% acid gas.

The cables are subjected to an IEC 60331-3 dry fire resistance test to meet the requirements of the standard. However, no water-based tests are included in the standard, but these can be carried out separately using special protocols for single core cables. Commonly, end users and regulators specify additional BS 6387 tests for single core fire resistant cables. All the tests can be carried out in the BASEC cable tests laboratory.

International impact

This cable type is commonly used across the Middle East and Asia in critical emergency circuits so it is important for specifiers and fire engineers working in these regions to be aware of the new standard. In locations such as the United Arab Emirates and Hong Kong, where steel reinforced concrete construction is widely used, the buildings often use embedded conduit for power, lighting and safety circuitry.

The reason for this is that it is easier to use small single core cables than larger sheathed cables with this construction method. This differs from the usual construction practices in the UK and Europe, where sheathed cables are more commonly used for emergency circuits.

BASEC has an international program supporting reputable cable manufacturers to provide independent technical information to educate and inform engineers about new fire standards and revisions to ensure they are fully conversant with up to date fire cable regulations.

Cable test and certification bodies, such as BASEC, cannot test cables for every fire-related eventuality, however, by having consistent testing methods detailed in product standards such as BS 8592:2016, it ensures that cable products provided by manufacturers for test can be directly compared to a specification to ensure performance is benchmarked.

BS 7629-1 streamlined in new edition

The 2015 revision of BS 7629-1 has cleared the clutter from the standard and tightened requirements to prevent any misunderstandings in the supply chain. This revision impacts any UK fire alarm system (BS 5839-1) and emergency lighting system (BS 5266-1) where circuit integrity is needed.

For some time, there had been industry demand to bring the BS 5839-1 specified test methods and grading scheme into the product standard to simplify the specification process. Since its publication late last year, the revision has generally been well received.

Clearer marking and grading

The cable marking requirements are now quite specific. A number of fire test standards such as BS EN 50200 and BS 8434-2, codes of practice such as BS 5266-1, BS 5839-1 and BS 8519 and performance levels PH15, PH30, up to PH120 were not previously controlled and now, cannot be marked on BS 7629-1 cable. Some markings were becoming very long and complex which was unintentionally causing confusion.

However, where there was no requirement for fire performance markings on the external sheath in the 2008 version, BS 7629-1:2015 necessitates that for cables meeting the fire test requirements for categories ‘Standard 30’, ‘Standard 60’, or ‘Enhanced 120’, this grading is to be marked accordingly on the sheath.

It also requires that if a third party independent approval organisation is used, such as BASEC, its mark of approval shall be embossed, indented or printed throughout the length of the external cable sheath.

Cable test changes

An important revision has been a change to the assessment of the tin coating of the circuit protective conductor / drain wire. This coating helps prevent possible long term corrosion, which could affect performance in use.

The new test appears less prone to interference from scraping damage caused when making or disassembling the cable, however prior to its publication, there was a lot of debate about the test and whether it should even be included in this standard.  Many products were found to not be compliant to the old test (EN 1360:2002 Clause 5) which could delay the granting of product approval until necessary changes to the tinning process were achieved, usually to add additional tin. In practise, it has had a positive outcome and UKAS has now accredited BASEC to conduct the new test.

One of the notable fire resistance test revisions is that BS 6387 categories C, W, and Z have been removed from the standard. These include the traditional water-based test. However, these tests may still be conducted, and marked on the cable. We expect the new classes of performance to be incorporated into future revisions of Codes of Practice such as BS 5839-1 (Fire alarm and detection systems) and BS 5266 (emergency lighting).

Also, additional tests have been included for shrinkage of insulation and sheathing for the first time (generally applied to a number of other cable standards – EN 50525 series, BS 7211, BS 5467, BS 6724, BS 7846).

Both these new cable standards, BS 8592:2016 and BS 7629-1:2015, define specifications for fire resistant cables providing circuit integrity. As such they are excluded from the introduction of new Construction Products Regulation (CPR) requirements for reaction to fire for cables, which is underway now. BASEC has been appointed a Notified Body for the delivery of the full range of CPR cable services.

For more information, go to www.basec.org.uk

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Dr Jeremy Hodge is Chief Executive at the British Approvals Service for Cables (BASEC).

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