Many modern farms consist of a number of separate buildings, not all of which are intended for use by livestock. This article explains the requirements of BS 7671 for supplementary bonding in locations where it is intended to keep livestock.
Such locations include the milking parlour shown pictured below, where protection against indirect contact is provided by Earthed Equipotential Bonding and Automatic Disconnection of supply (EEBAD).
For agricultural premises, except for any dwellings intended solely for human habitation, the general requirements of BS 7671 are supplemented and modified by the requirements of Section 605 (Agricultural and Horticultural Premises).
One of the additional safety measures required by Section 605 is supplementary equipotential bonding in locations intended for livestock (Regulation Group 605-08 refers). The bonding should be arranged as explained later in this article.
Items to be connected together by supplementary bonding
The supplementary bonding required by Section 605 has to connect together the following conductive parts where these can be touched by livestock:
- exposed-conductive-parts, such as metallic enclosures of Class I switchgear, controlgear, accessories or current-using equipment; metal conduit or metal trunking, and
- extraneous-conductive-parts, such as exposed structural metalwork or metal fence posts, where such metalwork is likely to come into electrical contact with the general mass of Earth.
The purpose of the supplementary bonding is to assist in limiting the magnitude of voltages occurring between conductive parts under earth fault conditions, so as not to cause danger to livestock.
Bonding conductors
The supplementary bonding conductors, whether of copper or another metal, must have a cross-sectional area not less than that required by Regulation Group 547-03 of BS 7671. Attention should be paid to the protection of the conductors against mechanical damage and to the avoidance of corrosion, particularly at connections.
Connections should preferably be made accessible for inspection, testing and maintenance. Where not accessible, connections are required to be made by one of the methods listed in Regulation 526-04-01, such as welding, soldering or brazing.
To read full article please download attachment...