20V AC present even with light switch off!

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Old 09-27-17, 10:09 PM
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Question 20V AC present even with light switch off!

I had a flood from washing machine in the upstairs floor. I removed the main floor ceiling light fixture and found 120V at the light fixture wiring, with the wall light switch on. BUT I also found 20V AC with the light switch OFF. How is this possible?
There are actually two light switches that control that light fixture, not that I could imagine that that influences it.
There's no remaining water that I could see near the light fixture wiring (now 4-5 days after the flood).
A very strange problem to me!
 
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Old 09-27-17, 10:52 PM
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I also found 20V AC with the light switch OFF. How is this possible?
I'll guess you were using a common cheap digital multimeter not an analog multimeter. Without special circuits a digital meter will react to induced voltages from nearby sources. Even a cheap analog meter because of its low impedance will usually not show ghost voltages.
 
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Old 09-28-17, 05:41 AM
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Ok it's actually a relief if that's the problem. I haven't noticed false readings before with this DMM. The reviews say it's as accurate as a Fluke for some things but I wouldn't know. Maybe I will check other switch circuits to see if I see the same behavior. I was concerned the water damage somehow affected the circuit but I can't see how.
 
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Old 09-28-17, 06:48 AM
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Fluke does have a digital with a special circuit for AC but it is more than $100 but a $10 analog meter will do just as well.
 
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