2

I wanted to find the breaker for directly wired (i.e. no plug + outlet) dishwasher by using a 'non-contact voltage tester' and it showed +ve for three different breakers. Then I hooked up a multimeter (V/AC setting) and tested. The reading for three breakers were 120V, 13.7V and 1.7V.

What could be the cause for the last two? Induction when wires run parallel? Insulation deterioration over time? Neutral is not at 0v? I suspected induction because when the last two breakers both on the voltage drops to 1.3V. However 13.7V seems too high, not that I know anything about what it should be.

The house is 37 years old, but probably it was rewired sometime later.

  • What's the maximum voltage you should see on a multi-meter, from a (NCV false positive) induced current? Good question. – Mazura Oct 31 '16 at 6:55
  • There's a few sentence fragments in there; a bit more editing would help us better understand what you're talking about. – Daniel Griscom Oct 31 '16 at 11:35
2

Your thoughts about induced voltage is correct when wires are run in parallel the field created on the live wires induces voltages on the conductors of the other circuits (this is how transformers work). Non contact meters read the field voltage and most hand held meters are high impedance so they will also show voltages. A low impedance or low Z meter creates enough of a load to eliminate the "phantom voltages" as many people call them. The voltages you are reading are quite low and nothing to be concerned about.

| improve this answer | |
  • Thanks for explaining the impedance part. Next time I will load it with a light bulb or something like that. Thanks. – Aelian Nov 10 '16 at 22:12

Not the answer you're looking for? Browse other questions tagged or ask your own question.