The fields in your walls, and what can actually be done about them
This site continues the subject of a small, remarkable book that quietly went out of print - and never stopped being cited.
In 2001, a physicist named Edward A. Leeper published Silencing the Fields: A Practical Guide to Reducing AC Magnetic Fields through Symmetry Books of Boulder, Colorado. Leeper was not a newcomer to the subject. Two decades earlier, with epidemiologist Nancy Wertheimer, he had co-authored the 1979 study in the American Journal of Epidemiology that first reported an association between residential electrical wiring configurations and childhood cancer - the paper that effectively created the modern field of research into power-frequency magnetic fields. The "Wertheimer–Leeper wire code" for classifying residential exposure still carries their names in the epidemiology literature.
What made Silencing the Fields unusual was its temperament. Leeper was cautious about health claims - he did not argue that household magnetic fields had been proven harmful, and he had little patience for the industry of alarm that grew up around EMF. What he offered instead was something more durable: a clear, physically rigorous explanation of why elevated 60 Hz magnetic fields occur in ordinary homes, how to measure them with an inexpensive gaussmeter, and how to fix them at the source - usually by finding and correcting the wiring conditions and plumbing currents that create them.
The book has been out of print for years. Used copies routinely list for several hundred dollars, and it is still recommended by electricians on the Mike Holt code forums, by audio engineers chasing hum on recording forums, and in the instruction manuals of gaussmeter manufacturers. The domain that once sold it went dark. This site exists to keep the subject - and the practical, measurement-first approach Leeper championed - available to the people who keep looking for it.
Start here
The three ideas below are the spine of the whole subject. Each links to a fuller explanation.
| Idea | In one sentence |
|---|---|
| Net current is the villain | Elevated magnetic fields in homes are almost always caused by net current - current flowing out on one path and returning on another, most often via metal water pipes or wiring errors. |
| Measure before you conclude | A consumer gaussmeter costing less than a nice dinner will tell you more about your home than any amount of speculation. |
| You cannot shield your way out | Power-frequency magnetic fields pass through brick, drywall, aluminum, and lead almost as if they were not there; the fix is at the source, not in the walls. |
On the health question
This site takes the same position the book did. In 2002, the International Agency for Research on Cancer classified extremely-low-frequency magnetic fields as a Group 2B agent - "possibly carcinogenic to humans" - a category that reflects limited epidemiological evidence and an absence of established mechanism, not a proven hazard. Research summaries from the National Institute of Environmental Health Sciences remain the sensible starting point. Many people, having read the same evidence, reasonably choose prudent avoidance: if a strong field in a bedroom can be eliminated by fixing a wiring error that shouldn't exist anyway, there is no reason not to. That is the spirit of everything published here.
About this site
This site does not sell the book - see About the Book for what each part of it covered and where copies occasionally surface. Corrections and suggestions are welcome.