The IEE’s Technical Helpline receives numerous calls from contractors requesting information on the earthing and bonding requirements for hazardous locations. This article will give an overview of the hazards and problems encountered in those locations.
1. Introduction
This article will give an overview of the hazards and problems encountered in those locations and gives information on the performance requirements of earthing and bonding to ensure that the potential for gas ignition, from low voltage electrical sources and equipment, is reduced.
2. The Regulations
BS 7671, Requirements for Electrical Installations, is intended to be applied to electrical installations generally but, in certain cases, they may need to be supplemented by the requirements or recommendations of other British Standards or by the requirements of the person ordering the work.
Such cases would include the following:
- Electrical apparatus for explosive gas atmospheres – BS EN 60079
- Electrical apparatus for use in the presence of combustible dust – BS EN 50281
3. Definitions
Often, there is great confusion over earthing, bonding and even use of the nonsensical term, earth-bonding! BS 7671, Requirements for Electrical Installations, defines:
Earthing – ‘Connection of the exposed-conductiveparts of an installation to the main earthing terminal of that installation.’
Bonding – the correct title is ‘Equipotential bonding’.
Electrical connection maintaining various exposed-conductive-parts and extraneous-conductive-parts at substantially the same potential’
There are two categories of equipotential bonding:
Main equipotential bonding
Regulation 413-02-02 of BS 7671 states: In each installation, main equipotential bonding conductors shall connect to the main earthing terminal extraneous conductive-parts of that installation.
Supplementary equipotential bonding
Regulation 413-02-27 of BS 7671 states: Where supplementary equipotential bonding is necessary, it shall connect together the exposed conductive-parts of equipment in the circuits concerned and extraneous-conductive-parts.
Supplementary equipotential bonding is not required on every installation, generally however, it is required in areas of increased risk; BS 7671 recognises these areas as ‘Special Locations’. A hazardous location, of course, would be considered as a special location.
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