SECTION 422
422 PRECAUTIONS WHERE PARTICULAR RISKS OF FIRE EXIST
422.2 Protected escape routes
Cables or other electrical equipment shall not be installed in a firefighting lobby, shaft or staircase of a protected escape route unless part of:
(i) an essential fire safety or related safety system;
(ii) general needs lighting;
(iii) socket-outlets provided for cleaning or maintenance.
NOTE 1: Guidance is provided in Appendix 13.
NOTE 2: Generally, this means cables in a firefighting lobby, shaft or staircase of a protected escape route should be limited to lighting and associated accessories, emergency lighting and fire detection and alarm systems, although cables for other safety systems may be necessary. Hospitals may have special requirements as detailed in Section 710.
SECTION 443
443 PROTECTION AGAINST TRANSIENT OVERVOLTAGES OF ATMOSPHERIC ORIGIN OR DUE TO SWITCHING
443.4.1 Transient over voltages due to the effects of indirect lightning strokes
Protection against transient over voltages shall be provided where the consequence caused by the overvoltage could result in:
(i) serious injury to, or loss of, human life;
(ii) failure of a safety service, as defined in Part 2- this has been deleted by BS 7671:2018+A2:2022, Corrigendum (May 2023);
(iii) significant financial or data loss.
– For all other cases, protection against transient over voltages shall be provided unless the owner of the installation declares it is not required due to any loss or damage being tolerable and they accept the risk of damage to equipment and any consequential loss.
443.6.2 Rated impulse voltages of equipment and overvoltage categories:
– Category IV equipment is suitable for use at, or in the proximity of, the origin of the electrical installation, for example, upstream of the main distribution board. Equipment of category IV has a very high impulse withstand
capability providing the required high degree of reliability, and shall have a rated impulse voltage not less than the value specified in Table 443.2.
– Category III equipment is suitable for use in the fixed installation downstream of and including the main distribution board, providing a high degree of availability, and shall have a rated impulse voltage not less than the value specified in Table 443.2.
– Category II equipment is suitable for connection to the fixed installation, providing a degree of availability normally required for current-using equipment, and shall have a rated impulse voltage not less than the value specified in Table 443.2.
– Category I equipment is only suitable for use in the fixed installation where SPDs are installed outside the equipment to limit transient over voltages to the specified level, and shall have a rated impulse voltage not less than the value
specified in Table 443.2. Therefore, equipment with a rated impulse voltage corresponding to overvoltage Category I should, preferably, not be installed at or near the origin of the installation.
SECTION 534
534 DEVICES FOR PROTECTION AGAINST OVERVOLTAGE
534.4.1.1 Where SPDs are required:
(i) SPDs installed at the origin of the electrical installation shall be Type 1 or Type 2;
(ii) SPDs installed close to sensitive equipment to further protect against switching transients originating within the building shall be Type 2 or Type 3.
– NOTE: Type 1 SPDs are often referred to as equipotential bonding SPDs and are fitted at the origin of the electrical installation to specifically prevent dangerous sparking which could lead to fire or electric shock hazards. In accordance with BS EN 62305-4, a lightning protection system which only employs equipotential bonding SPDs provides no effective protection against failure of sensitive electrical and electronic systems. Further SPDs (Type 2 and Type 3) are required to protect sensitive and critical equipment (for example, hospital equipment)
downstream of the origin of the electrical installation.
Conclusion
Electrical installations are a critical aspect of our modern lives, and their proper maintenance and safety measures should never be overlooked. Regular fault finding, condition reports, and certification ensure that installations function optimally, minimizing the risk of accidents or electrical failures. Additionally, emergency lighting and fire detection systems provide an added layer of safety, offering peace of mind to occupants. By prioritizing the safety and efficiency of electrical installations, we can create a secure environment for everyone.
Leave a Reply