Electrical services Fault reduction Lurking When it
comes to operational risk management, protection against electrical faults is a top priority
M
odern built environments are becoming more complex as a wider range of services systems are being integrated under one roof – from lighting and power
distribution to intelligent control and data networks. This complexity is placing increasing challenges on electrical designers and installers to provide clients with a carbon friendly, energy efficient, safe and robust electrical building services system. Any system downtime arising from electrical maintenance or clearance of faults needs to be minimised using a well-designed protection scheme: the impact of the downtime on the day-to-day activities within the building – including potential loss of revenues – has to be reduced to a minimum. Clearly, when it comes to operational risk management, protection against electrical faults is a top priority. The duty of care that a professional engineer owes
to the client cannot be delegated, which makes the engineer responsible for producing a safe and robust design. On pages 58 to 59 we provide a simple 15-step ‘fault MVA (megavolt-ampere) calculation method’ aimed at helping designers and installers to check the level of fault currents that could be lurking in an electrical system.
Electrical standards There are relevant national electrical rules such as BS7671 and NEC, and international standards from the IEEE, IEC and BSI that designers and installers can use to ensure electrical equipment and cables are adequately protected against dangerous fault
56 CIBSE Journal September 2010
Electrical engineers are facing increasing challenges to lower the risk of faults as more complex systems and services are installed in buildings. Tony Sung offers a guide to checking for faults
faults
currents. Protection of electrical installations against fault currents in the built environment can range from simple dwellings to a highly complex type of building such as an airport or hospital. For simple domestic dwellings that receive a single phase AC supply from the supply utility company, the fault current protection design can be implemented using rules of thumb; advice is also available in guidance materials published by trade bodies and professional learned societies. As for more-sophisticated buildings that contain
HV/LV transformers and complex distribution equipment on site, electrical building services engineers are required to devise a bespoke overcurrents protection scheme to provide correct discrimination to disconnect and isolate overcurrents and earth faults without
BS7671: 2008 – 17th edition IEE Wiring Regulations states that:
Regulation 132.13 Documentation for the electrical installation Every electrical installation shall be provided with appropriate documentation, including that required by Regulation 514.9, Part 6 and where applicable Part 7.
Regulation 434.1 Determination of Prospective fault current The prospective fault current shall be determined at every relevant point of the installation. This shall be done by calculation, measurement or enquiry.
(The authors acknowledge the permission granted by the IET to reproduce the above regulations from BS7671:2008)
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