Electrical live on a switched circut?
OldSaw
| Posted in Construction Techniques on
I am doing a minor remodel in my den. I tapped into the 50-year old lighting circut to add a couple of cans over some new built-in’s I’m doing. Power runs from the box to a dimmer switch (which is actually a three-way) and then on to the lights. While I was working, I wired a plug to the end of the wire just to check and make sure the switch was all wired up OK. When I checked it with a meter, I found that it shows 116v when the switch is ON (no surprises so far) but it also shows 60v when the switch is OFF. Question to the electricians of the crowd: is this right? Did I do something wrong?
Thanks.
“Honey, will you please make some sawdust and track it across the carpet?”
“Yes, dear…”
Replies
It's probably "phantom" or "ghost" voltage, the result of capacitive coupling between a live wire and an unenergized one. The live wire has a kind of static electricity build up on the insulation and it bleeds over to the other wire. The voltage is real, but there's no current associated with it (well, maybe a microamp or two).
You're using a digital multimeter for the measurement, right? A DMM doesn't put any load on the circuit under test, so it's just measuring a difference in potential (voltage) due to the charge buildup. An analog meter (with a mechanical linkage and a needle) or a solenoidal tester puts a load on the circuit and dissipates the false voltage, consequently giving an accurate zero reading.
A poor man's way to check this is to put a load across the wires. A light bulb, for instance. With the lamp in the circuit, the DMM will give a true zero reading. This means screwing around with test clips and if the circuit is energized, subjecting yourself to a greater chance of getting shocked or electrocuted than if you used the right tool--an electrical voltage tester.
My fave is the Ideal Vol-Con Elite with shaker The Ideal Vol-con is good, as is the Square-D Wiggy. Gardner-bender and every other manufacturer makes a solenoidal tester. Figure about $30 for a basic one or $70 for the Vol-Con elite. Don't skimp on this tool, your life depends on it--if you're going to be messing with your wiring.
Cliff
Standard answer #27.
happy?
Hey Saw,
I'm no electrician,so wait to get a real answer. I've had the same thing happen to me, and I think somebody called it phantom or ghost voltage. Usually very low amps some kind of bleed thru volts.Almost impossible to trace. Any volts neutral to ground?Any volts ground to ground?
You not alone !
DAVE