2

just installed 2 new separate ceiling lights each with its own wall switch. The 2 wall switches sit beside each other. With analogue voltmeter I noted when both circuits are switched off there is 0 voltage across black/white wires on both circuit 1 and 2. But when circuit 1 is switched on and showing 120v, circuit 2 even though switched off, shows about 12 volts. Same occurs when circuit 2 is on and circuit 1 off. I presume this is just phantom voltage and not too worry? or could it be something that needs repairing? House built in 1975, aluminum wires.

also, I installed new lights to replace the integrated LED units, one of which had broken down twice. The first time the LED unit lasted 4 yrs and started flashing and then went dim. Replaced with same unit from Lowes, it lasted 4 months and went dim. Still don't know why LED units failed, wondered if related to voltage issues. I replaced with standard fixtures.

Improve this question
4
  • Do the cables for the two circuits run next to each other?
    – ThreePhaseEel
    Commented Nov 21, 2019 at 5:21
  • Hello, and welcome to Home Improvement. You're right to note the type of voltmeter; I'd expect yours not to show phantom voltages. And, you should probably take our tour so you'll know how best to participate here.
    – Daniel Griscom
    Commented Nov 21, 2019 at 10:51
  • @ThreePhaseEel I suspect that cables for the two circuits run next to each other behind the wall and for ~4 feet in ceiling
    – Ben Tunite
    Commented Nov 22, 2019 at 20:59
  • @DanielGriscom voltmeter is an old radioshack Micronta 22-211 indicating 10,000 Ohms / Volt AC, not sure if this is a low enough impedance
    – Ben Tunite
    Commented Nov 22, 2019 at 21:05

1 Answer 1

Reset to default
2

This is called phantom voltage. When a cable is powering a device a field is generated, this field then induces a voltage on any wires in close proximity to the live wire. There is no problem here, this is related to how transformers work. I have seen phantom voltages close to the line voltage where there is a long run of multiple cables in parallel. The higher impedance the meter, the higher the voltage will be displayed. Their are low-Z or impedance meters that load the circuit enough to dampen the phantom voltages. But low-Z meters are not as sensitive for accurate measurements of electronic circuits so they are somewhat uncommon. I would not worry.

Improve this answer
3
  • Which suggests this can be verified by sticking a low-value resistor across the Switch2 feed and seeing if the voltmeter now reads zero.
    – Carl Witthoft
    Commented Nov 21, 2019 at 19:25
  • Note that some modern DMMs have a low-Z function (such as my Brymen BM235, for one)
    – ThreePhaseEel
    Commented Nov 22, 2019 at 1:21
  • I have a fluke that can do low z also but most home owners or diy really won’t pay even close 100$ for a meter with low z when they can get all the other specs for 50$ Or less. Recently I have to really have long conversations with apprentices they want to go cheap and buy a new one every other year. But yes they are out there.
    – Ed Beal
    Commented Nov 22, 2019 at 2:58

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

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