According to the Copper Development Association, the use of four-core electrical cable is wasting resources and presenting a real risk of fire or unplanned shutdown in many industrial establishments. But, although a simple solution exists, Britain’s cable manufacturers seem to be unwilling, rather than unable, to address the problem. Four-core cable and distribution systems have formed the basis of power distribution in UK offices for so long that few engineers would consider an alternative. Yet there is growing evidence that alternatives are needed. The operation of modern electronic equipment means that the old four-core cables are no longer adequate for modern installations and their continued use means that many sites run a risk of cable overheating, failure, fire and electrocution from inadequate earthing.
Electronic equipment generates harmonic currents. In a three-phase system, these currents can reinforce in the neutral wire to produce currents that are twice the size of those flowing in the phase conductors. Ideally, therefore, a cable should have a neutral twice the size of the phases. This is, according to the cable makers, impractical as different core sizes would complicate the manufacturing process and require different fittings.
A four-core cable is also open to earthing difficulties. Earth currents caused by voltage differentials, wiring faults or compound earth leakage are common problems. In a three-phase system, these must be directed through a separate dual earth cable, through the cable armouring, or into the building infrastructure. None of these solutions is ideal. The solution is simple: use five- or six-core cables instead. News International is one company that has. When it found that the neutral conductors in its production room were carrying a current of 150A compared with only 100A in the phase, the company’s engineers decided to convert all critical areas to a five-core system instead.
The irony is that News International had to go to Italy to buy the cable. UK manufacturers are reluctant to supply the product until there’s a market for it!