In low voltage systems below 600 A are generally provided by multicore cables. Because of some installation problems the larger sizes need single-core cables to provide the necessary capacity.
The installation of single-core armoured cables requires care because generally there is a considerable current circulating in the armouring. The rating of the circuit depends on how the cables are laid, i.e. in trefoil, flat touching or flat separated. The use of two cables per phase is not unusual and these should be laid in accordance with the manufacturer’s instructions to avoid overheating within a cable or at the terminations.
Single-core cables may cause overheating of adjacent metalwork and can also produce high induced voltages under fault conditions. They are also a source of interference unless suitable precautions are taken to segregate them from sensitive equipment.