All of the wiring for the direct-wired undercabinet lights on one side of our newly remodeled kitchen was staying hot, regardless of the action of the light switch. Even the follower in the string of lights, supposedly just a loop of wire hanging in the wall, were showing hot. The only way to turn them off was to trip the GFCI to interrupt the >outlets< on that side of the kitchen. I was utterly mystified---I couldn't see any way to make the circut do that, short of actually wiring it for that behavior on purpose. Just before I called the electrician to come back and figure out what he had done wrong, I tried one more thing:
I was testing for current with a non-contact, inductive tester. The electrician had stapled one of the followers in the string of lights alongside the cable for the nearby outlet, literally with the same set of staples. Further up the line, the cables for the lights were twisted together for convenience. It looks like the light wiring was acting as an antenna, carrying just enough induced energy to activate the inductive tester. Testing with a directly connected test light , I found that the light wiring worked exactly as expected, turning just one hot lead on and off with the switch.
Apparently the results from these inductive circuit testers should be taken as a quick "suggestion" of what's going on. Does anyone have any other observations about the safety and effectiveness of thsse non-contact testers?