BS 7671: an introduction

BS 7671: 2008 is the National Standard for most electrical installation work undertaken in the United Kingdom.
It is also adopted by a number of other Countries in the World.
The first edition of BS 7671 was published in 1992 when the British Standards Institution (BSI) adopted the IEE Wiring Regulations, 16th Edition and made it a National Standard.
The British Electrotechnical Committee (BEC) is part of the British Standard Institution (BSI) and is the UK member of the International Electrotechnical Commission (IEC) and the European Committee for Electrotechnical Standardisation (CENELEC).
The purpose of IEC and CENELEC is to create commonality of Electrical Installation Standards throughout the World and Europe respectively. The standards thus created are known as Harmonised Documents (HDs).

BS 7671 is the UK collection of HDs incorporated in a single publication with many other regulations that accommodate specific situations and practices applicable in the UK. A number of countries adopt BS 7671 as their national standard and others base their national standard on BS 7671.

BS 7671 has been amended six times since the first publication in 1992 as HDs have been revised or new HDs published. The 17th Edition is the result of a complete review of the 16th Edition and adopts all HDs that are published to date.

The principal hazards envisaged by the statutory regulations relate both to electrical machines and other current-using equipment and to the fixed installation. BS 7671 addresses the requirements for safety for fixed installations, where the hazards are perceived to be:

• shock currents;
• excessive temperatures likely to cause burns, fires and other injurious effects;
• ignition of potentially explosive atmosphere;
• undervoltages, overvoltages and electromagnetic influences likely to cause or result in injury or damage;
• mechanical movement of electrically actuated equipment, in so far as such injury is intended to be prevented by electrical emergency switching or by electrical switching for mechanical maintenance of nonelectrical parts of such equipment;
• power supply interruptions and/or interruption of safety services;
• arcing, likely to cause blinding effects, excessive pressure and/or toxic gases.

Every installation must be inspected and tested during erection and on completion before being put into service to verify, so far as is reasonably practicable, that the requirements of the Regulations have been met.

 The Testing Checklist includes:

• continuity of conductors
• insulation resistance
• polarity
• earth electrode resistance (TT systems)
• earth fault loop impedance (TN systems)
• functional testing
• verification of voltage drop

The Health and Safety Executive (HSE), in a note to BS 7671, states that it regards an electrical installation carried out in accordance with the requirements of BS 7671 as likely also to afford compliance (Principio di presunzione di conformità!) with the relevant aspects of the Electricity at Work Regulations 1989.

GT Engineering can support you in all aspects related to the compliance with the BS 7671.