What are net currents?
Substations supplying an area with electricity are interconnected in a way that is intended to ensure a constant voltage supply, to avoid equipment malfunction. Some properties have high levels of magnetic fields as a result of a fault or faults having developed in the supply cables between two substations. This produces an unbalanced or net current. The net current forms a loop between the substations and because it isn’t balanced out by a current in the opposite direction (as it would be in a single cable carrying both ‘go’ and ‘return’ currents) then it can create quite high EMFs over a wide area. Magnetic fields coming into a property from outside are usually from underground cables carrying the power supply from house to house, often running under the pavement outside. If there is no front garden or the property is a basement flat, the magnetic fields could be quite high even without net currents, but should fall off rapidly as you move away from the cables by a couple of metres.
