Setting: 60 yr old house with conduit/bx in Chic suburbs. Man agrees to wife's request to move a light fixture one foot. Man has owned the house for 20 years, done many projects (including electrical). Turning 50 on this very day, the man decides "today is the day" and slides the screwdriver into the first slot...
Problem: After taking down old light, I discovered a 30v reading at the ceiling with switch in off position. Disconnected wire from switch and it still read 30. Measured newly disconnected end out of switch box - 30. (BTW-testing to box.)
My Hypothesis: This is either the long-dead magician come back to taunt this DIY-er or (more likely) I don't have the ends of the wire I thought I did or ...?
Question: Is there anything else that would cause this reading? The hot wire is free on both ends (or so I think) but it still reads 30v.
Inductive or phantom voltage. You are measuring the "voltage" on a disconnected wire that is in close proximity to another wire that is still connected. The characteristics of A/C would produce those kind of false positive readings.
Try using a solenoid loaded tester, or put a load on the wire and measure again.
Life is uncertain -- eat dessert first!!
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