Residential magnetic fields, contact voltage and their relationship: the effects of distribution unbalance and residential proximity to a transmission line.

In previous studies, modeling and measurements have suggested a positive relationship between the average residential magnetic field (B(avg)) and the voltage from the residential water line to earth (V(W-E)). This voltage is the source of exposure to contact current that has been hypothesized to behave as a confounder with respect to the association between residential magnetic fields and childhood leukemia. The previous modeling effort has only considered the influence of distribution lines on the B(avg):V(W-E) relationship. This study extends that analysis to include the effect of distribution line unbalance and the presence of nearby transmission lines. The results show that, compared to balanced systems, unbalanced distribution systems had increased B(avg) and V(W-E), with a relatively greater effect on (VW-E). The presence of a transmission line proportionally increased B(avg) and V(W-E) more on balanced systems than unbalanced systems and attenuated the relationship of B(avg) with V(W-E) on systems with 25% unbalance. Increases in B(avg) due to the transmission line were confined to distances within 100-200 m of the line, but increases in V(W-E) extended to the furthest distance included in the model (365 m). The observations reported may be relevant to prior epidemiological studies of magnetic fields and childhood leukemia, and suggest that research efforts continue to explore the role of contact current in potentially explaining those studies.