I'm not sure how that indicates a code violation or damage to wiring, but EMF levels above 4mG are suspected to cause leukemia.
You'd measure it by walking around the house with a probe. Strongest levels would be near the wiring.
I suppose it could indicate that you have leakage current or a multigrounded neutral, as the currenet in the hot conductors and neutral will always be opposite and the subsequent magnetic fields almost perfectly cancel each other out... Just don't use a hairdryer as your load- they put out something like 300 milligauss at 6'!
