NO GROUND FOR LOOPHOLES

There are two new items on EM fields and child leukemia this month, and Mr. Brodeur is not going to like either of them.

First, experiments and correlations by the Research Division of Ontario Hydro in Toronto leave little doubt that the magnetic field in a residence due to both power lines and appliances is over-shadowed in a ratio of 3:1 by another cause, ground loops. To understand this mechanism, one needs to consider current loops and three-phase currents.

A current is continuous: it must flow from the source (say, the power plant) back to the source. It also always has a magnetic field. When the current from the source and back flows through parallel wires, as it does in the leads to an appliance, the conduc-tors carry equal currents in opposite directions, and their magnetic field almost cancel, falling off very rapidly with distance from the two conductors. But if the current forms a loop, then inside this loop the magnetic fields of the current elements add and give rise to a comparatively strong field.

Next, an alternating current (AC) flows back and forth 60 times a second; a time chart of the voltage driving it looks like the thick sinusoid in the top figure. There are several advantages in supply- ing electricity simultaneously in three conductors, in each of which the voltage is time-shifted by 1/3^rd of a cycle as shown. This is known as three-phase current; its main advantage is its ability to produce a rotating field that carries the armature of an electric motor with it. For most residential purposes only one of the phases would be needed, but it is usual to connect dif- ferent parts of the house to different phases. If the loads on the three phases were exactly equal, no return wire would be needed, be- cause the current flow- ing in by one phase would flow back through the other two. But they are never ex- actly balanced, and the balancing current flows through a fourth con- ductor, which is grounded somewhere (preferably near the house). Inside the house, appliances are usually connected to the water plumbing to form a ground. The left house in the figure gets its supply from three phases and, ideally, the balancing current should flow back through its own ground conductor into the net. But the grounding contact to the plumbing is of different quality in every house, and the current goes by way of least resistance, which is often through the neighbors house or houses. The resulting loop shown by a thick line, has a far larger magnetic field than the ap-pliances in the house, let alone the parallel wires of the distribution lines.

Please note that I am talking about magnetic fields, not of any health effects which are alleged to be associated with them, but have never been demonstrated. The remedy, if one were needed, would be to insert plastic insulators between pipe sections (com-pared to metal, water is a poor conductor) and see to it that the local grounding (return circuit) is good. This is of no use to utility basher Brodeur, since both will have to be paid by the owner.

[Mote: D.L Mader and others, "A simple model for calculating residential 60- Hz magnetic fields, Bioelectromagnetics, vol .11, pp. 283-286 (1990).]