Transmission risks
the time temperature protocol used by BS 476 Parts 20 to 24 (EN 1363-1 or ISO 834-1) as a reasonable minimum requirement, and must cast doubt on the much lower test temperatures required today by British Standards test methods for fire resistant cables. To determine current ratings of fire rated
cables, I propose a ‘design fire’ at 1,000°C. Others may propose 950°C, which would give a little more head room and enable slightly higher current ratings. Of course, the common polymeric fire rated cables sold in the UK today would need to demonstrate that their design is capable of maintaining electrical integrity at 1,049°C, which currently they do not. For fire rated power cables commonly sold
in the UK today, using the standard tables in BS 7671: 2018 for the selection of maximum current ratings needed during a real fire emergency can be technically risky. Selection of a larger conductor size than suggested may be required to ensure that the operating current needed by the safety equipment during those conditions can be maintained during the fire. This means that it is necessary to ensure the cable chosen is capable (via testing) of maintaining reliable operation at the exposed fire temperature, including any additional current induced temperature rise
Richard Hosier is Asia/Pacific regional manager at MICC Ltd. For more information, view page 5
FOCUS
References
1. TI - 0401 Fire resistance. Testing, assessment and certification, Chiltern International Fire.
2. Babrauskas, Dr V, Temperatures in flames and fires, Fire Science and Technology Inc, 1997, revised 2006.
3. Ariyanayagam, A D, and Mahendran, M, Fire safety of buildings based on realistic fire time-temperature curves, QUT, 2013.
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