Customers often ask us why their power goes off, but their neighbours’ power stays on.
We supply power to your home or business at low voltage, either 230 or 400 volts. Power does not travel very far at these voltages, so we bring the power to your area at much higher voltage, usually 11,000 volts. We reduce the voltage in local substations and deliver the power to you through underground cables, overhead lines, or a mixture of both.
How your property is connected to our network
We usually use four wires for low voltage distribution. Three are live, called phases, and one is the neutral.
Domestic customers get their electricity from one of the three live phases and the neutral. We aim to connect an equal number of houses to each phase, although this might be randomly applied in a street.
When a fuse protecting one of the three phases blows only a third of the customers lose power. If two fuses blow then two thirds of the connected customers go off. You can see now how some customers can be without power while their immediate neighbours are not affected.
Keeping the power on
In urban areas, substations are relatively close together and often interconnect with each other. We can use link boxes in the footpath to alter these connections and keep your power on from a different substation while we work on our equipment. If there is a fault we may be able to get your power back this way too.
We can sometimes do this with the overhead lines in rural areas too. However, there is often less interconnection as the houses and substations tend to be further apart.
Underground cables are normally reliable if they are not disturbed. Common causes of cable faults included vibration and subsidence, and other companies digging nearby. Any damage to the cable allows water in the ground to get in and cause a breakdown. It may be months before the problem gets bad enough to cause a power cut.
Faults on low voltage underground cables can often be intermittent and very hard to find. If we can replace the fuses successfully it is usually because the heat from the fault has resealed the cable. We can only use our fault locating equipment once the fault has become permanent.
Overhead lines are more likely to be affected by lightning, windblow material , trees and birds or vermin causing short circuits.