SAGE Recommendations on house wiring.

More on SAGE.

In most homes, the house wiring is not a major source of magnetic fields. See more on what the usual sources of field are. But in some homes, some particular feature of the wiring means it does become a source of high field. About 0.4% of homes in the UK have fields greater than 0.4 µT, and in perhaps a quarter of these, the source is the house wiring. More on numbers of homes.

SAGE recommends a package of changes to house wiring that would remove or reduce these features in homes where they exist. In other homes, with normal wiring, these measures would make little difference to the fields.

Using radial power circuits instead of ring mains

With ring mains, normally, the phase (the strict term for what is usually called the "live") and neutral currents are balanced. But sometimes, for instance if there is a loose joint, the phase current may flow one way round the ring and the neutral current may flow the other way. This creates a large current loop which is a source of magnetic field.

SAGE recommends using radial circuits instead, which removes this possibility. But each ring main then becomes two radial circuits and so requires two fuses or circuit breakers at the consumer unit. These extra circuit breakers are a small extra cost for a new installation, but for an existing installation, this option could require fitting a whole new, larger, consumer unit.

Keeping "go" and "return" currents together

In most wiring, the "go" and "return" currents are in the same cable so are kept together anyway. Sometimes, however, they can become separated, forming a large loop which produces magnetic fields. The commonest example is with two-way switching of lights. Sometimes the easiest way to wire them involves creating a loop, but it is always possible to keep "go" and "return" together, and this is what SAGE recommends.

Keeping meter tails together

Because the meter tails (the wires from the electricity meter to the consumer unit) carry the whole load in the house, they can produce significant magnetic fields is they form a loop rather than being kept together. It is usually easy to keep them together and this is what SAGE recommends.

Require an RCD for the whole installation

Normally, there is no connection in a house between the neutral conductor and earth. But sometimes one can develop accidentally, for instance if the insulation on a neutral conductor corrodes, or if a screw cuts the insulation. Then current diverts out of the neutral into the earth, the phase and neutral are no longer balanced, and a significant magnetic field can be produced.

Fitting a Residual Current Device (RCD) does not stop this from happening. But if it does happen, it will trip the RCD, forcing the fault to be found and repaired.

RCDs are becoming more common and are likely to be required in the next edition of the Wiring Regulations anyway.

Phase out rotating disc electricity meters

The traditional electricity meter has a rotating disc, and the air gap in the magnetic core through which the disc rotates is a significant source of magnetic field. Electronic meters do not have this feature, so SAGE recommends rotating discs should be phased out. There is a trend to electronic meters anyway, but a lot of rotating disc meters are still in use and are sometimes refurbished and refitted.

Provide information for householders

This, of course, does not directly reduce fields, but allows the householder to make choices that could reduce their exposure.

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