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.
Thanks for any help or references on reading material to learn more!
MG
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Replies
There will be other explanations, but you are most likely reading the unbalanced load on the neutral.
No sweat. 1 volt is nothing to be concerned about.
Dave
Stray electrical pickup.
Contactless detectors and high-impedance detectors (like neon lights and some electronic meters) are just about useless on household electrical circuits unless you have a fairly good understanding of stray pickup.
Betcha you're using a digital meter? Their input impedence is too high for a meaningful reading in that situation and you're reading a phantom voltage, likely caused by the leads, or the cable acting as an antenna and giving you a reading that isn't really there...
Probably #6 most often asked elec question here ;)
HTH
PaulB
No the multimeter is analog, not sure if that matters.
That's odd... probably makes the phantom voltage theory less likely. May be some kind of unbalanced load. I'd be surprised if it was anything more than an oddity but I suspect one of the real electricians will be by to offer a worthwhile opinion.
A high impendence analog meter can still read some phanton voltage.Does this switch have a nigh light in it? Those are small neon lights that are in series and will allow a small current to flow.Is there a bulb in the light? No bulb and the the hot lead is just floating with the swtch off.Does the light work when the switch is on? If the light does not work then the neutral can be floating.
There is no light in the fixture. I just have the roughed in wire. There is no light in the switch either... just simple decora light switches with no dimmers.The reason I detected this is I was installing two 3-way switches which switch the black wire to this light and I was trying to determine if I had my wiring correct based on my contactless voltdetector telling me there is voltage or no voltage at the rough-in light fixture. In this case the 1volt difference caused me to believe the switches were not working.I think the light will work once installed as when i switch one of the 3-ways on then my multimeter detects ~120volts.Thanks again for all the responses!MG
In electronics, you want the highest impedance meter you can get, to minimize the effect the instrument has on the circuit under test. For power work, you want a low impedance meter so you only see the real solid connections, not coupling thru a tiny bit of capacitance.
The good news is that you can make any meter low impedance, just by putting it in parallel with a small incandescent light bulb. 15 watts works fine for this, or even a 7 1/2 watt Christmas lite.
-- J.S.
I thought I heard someone once refer to that as "ghost voltage" but I may be wrong...
There are a couple of things that might be happening... but the short version is, you probably have no need to worry.
A 'dead' wire, when it rund alongside a 'live' one, will often pick up some voltage. The ten-dollar word for this is 'induction.' This is voltage only; there is essentially no amperage available.. just enough 'oomph' to register on the meter.
Another source is a minor amount of voltage 'leaking' through the light switch. If you have illuminated switches, photocells, or timers, these items often let just a bit through by design.... that's how they continue working even when "off."
Any electronics, say, a fluorescent light ballast, may have capacitors to store up some electricity. You may be reading this charge 'bleeding down.'
And, finally, meters are nowhere near as precise as they may appear. That "1 volt" may just be in the imagination of the meter.
I generally ignore anything below one volt, unless I'm taking extra care to get a precise measurement. Galvanic action between the different metals, combined with moisture from your fingers, can create about a volt of potential on a poor connection.
If Tyranny and Oppression come to this land, it will be in the guise of fighting a foreign enemy. --James Madison