# 1volt detected at light fixture when switch off?

• posted on July 28, 2006, 6:00 pm
Hi,
I was hoping someone could tell me why my contactless volt detector detects voltage at my light fixture when the switch is off and my multimeter tells me there is a 1volt different b/t white and black. Should I be concerned?
I have a 15amp circuit that comes into the switch and is then passed onto the fixture. The fixture is probably the 9th item on the circuit.
MG

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• posted on July 28, 2006, 8:50 pm

The 1 volt you measured could be an induced voltage. If you put a load on it (e.g. screw back light bulb), it would probably drop to zero. Use your ingenuity to figure out how to put a load on it and measure the voltage at the same time :)

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• posted on July 28, 2006, 11:48 pm

It's called "AC coupling";the small capacitance of the switch itself is coupling voltage to the lamp.(google "capacitive reactance")
--
Jim Yanik
jyanik

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• posted on July 28, 2006, 8:52 pm

The voltmeter is a high impedence device. Voltage can be induced in the wire by the electric field where it is near other wires, but very little current will be available. The voltmeter doesn't draw much current, so it will display small voltage readings. Don't worry about it - especially if it's only 1 volt.
Bob

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• posted on July 28, 2006, 9:07 pm
One volt, heck I can get that reading by holding the voltmeter one of the voltmeter in each of my hands. That is one volt between my left and right hand.

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• posted on July 28, 2006, 9:54 pm
snipped-for-privacy@yahoo.com wrote:

Hi, Is it DVM?

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• posted on July 28, 2006, 11:34 pm

It could mean the neutral wire is being broken by the switch to turn off the light. That is what the contactless detector MAY be telling you. Those things are not very reliable to tell if voltage is present. They do a good job of telling of no voltage. The 1 volt differance could be just an induced voltage. When a wire is next to another wire , you have a 1 to 1 transformer. For just two wires next to each other the ammount of current that can be drawn is in the microamps or less. Many call this induced voltage. A voltmeter will load down this 1:1 voltage so that only a very small portion of the voltage is left. The lower the resistance of the voltmeter, the lowr the indicated voltage. A 20 meg ohm voltmeter may show 40 volts, a 20,000 ohm/volt (such as the old Simpson 260) may show 10 volts on the higher voltage scales. If you turn the selector switch to a lower range, the meter pointer will stay in nearly the same place instead of dropping much lower.

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• posted on July 29, 2006, 6:49 pm
snipped-for-privacy@yahoo.com wrote:

Those modern digital meters are just too sensitive. The measurement is almost certain to be nothing. AC induction
--
Joseph Meehan

Dia duit