Unit E3, Crown Way, Crown Park Industrial Estate, Rushden, Northants, UK, NN10 6FD Tel: +44 (0)1933 356758 Fax: +44 (0)1933 413821 Email: info@shrinkpolymersystems.co.uk Skype: shrinkpolymersystems www.shrinkpolymersystems.co.uk Earthing on Single Core Cables with Aluminium Wire Armours (AWA) If single core aluminium wire armoured (AWA) cables are earthed only at one end, a voltage will appear at the other end. If both ends are earthed, circulating currents will be induced. How much will depend on a number of factors: • Length of the cable run • The current in the cable conductor and its frequency 50Hz or 60Hz • The proximity of the other two cables, assuming a 3 phase system • The mutual inductance per phase The current can be calculated using the following method: Ic = V Amps Z Where Ic = Circulating current V = Induced voltage Z = Impedance of the sheath On long cable runs potentially lethal over voltages can be induced and standard earthing methods do not provide adequate protection. A simple method to reduce or eliminate this effect is to divide the cable run into three equal sections and install cross bond kits. Kits are available from SPS. Note: Installer would be well advised to obtain the parameters of the cable being installed from the cable manufacturer to enable values of induced voltage and current for a given situation. Heat Shrink Joint Heat Shrink Joint Heat Shrink Joint Typical Arrangement for Cross Bonding the Earth Straps to Alternate Phases 29
