Wall Dimmer Switch Anomaly?


My son recently replaced two wall on-off switches with dimmer switches, new from Home Depot or Lowe's, for me. They work fine and control incandescent lights. He discovered, however, that even when completely off about 48-50 volts still flow through the new dimmer switches - both of them.
We are both puzzled. We assumed that off would mean zero volts. If this is normal isn't it a safety hazard?
Any insight appreciated.
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CWLee
Former slayer of dragons; practice now limited to sacred
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CWLee wrote:

40 or 50 volts is enough to make incandescent bulbs glow. Are the bulb loads connected, and if so, do they glow?
If the loads aren't connected I'm guessing you have a limited knowledge of electronics and are probably measuring the output of those dimmers with an electronic (digital) voltmeter which is responding to miniscule leakage currents that give you what's known as "phantom" voltage readings.
If connected bulb loads "turn off" OK, fughedit.
HTH,
Jeff
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Jeffry Wisnia
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That digital meter thing - is it only an issue with AC current?
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JoeSpareBedroom wrote:

That depends on how those microamp sized currents are being coupled to the meter.
On AC, just capacitive coupling between two nearby insulated wires will cause current flow into the meter through the charging and discharging of the interwire capacitance. That current develops a voltage across the meter's input impedance which gets displayed. But, there coan also be resistive coupling of AC through badly degraded insulation on very old wiring, or through a film of moisture condensed across an insulating barrier.
On DC circuits capacitive coupling is not a factor, except perhaps for a momentary "blip" of the meter when an adjacent wire is powered up or down, but the resistive coupling mentioned above could easily cause a significant DC reading on a high input impedance meter.
My "rule of thumb" when encountering those unexpected low voltage digital meter readings is to put my thumb and forefinger across both meter probes while they are connected across the circuit. If the shunt resistance of my hand causes the meter reading to drop significantly, I know it's nothing to worry about.
YMMV, and to be safe, make sure you're not standing in a puddle or have your other hand on something grounded if you try that.
Jeff
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"40 or 50 volts is enough to make incandescent bulbs glow. Are the bulb loads connected, and if so, do they glow?"
At full ON the bulbs are very bright. As the toggle lever is moved toward the OFF position the bulbs diminish in brightness. With the lever horizontal (i.e., about half way between full ON and full OFF) the bulbs have dimmed sufficient that one can barely see the lighted filament inside. Moving the lever farther toward the full OFF position results in that barely lighted filament appearing to disappear. However, I wonder if, at 48-50 volts, the filament is hot enough to be visible through the frosted bulbs.
He also wrote:
"If the loads aren't connected I'm guessing you have a limited knowledge of electronics and are probably measuring the output of those dimmers with an electronic (digital) voltmeter which is responding to miniscule leakage currents that give you what's known as "phantom" voltage readings."
True, I have a limited knowledge of electronics. The output was measured with a (medium priced - perhaps $40 from Sears) hand-held digital voltmeter, as follows: Line voltage of 110? AC was on one side of the dimmer switch. At full ON the voltmeter read something like 116 or 118 volts. As the toggle lever on the switch was moved from full ON to full OFF the reading on the voltmeter dropped from 116 to 48 or 49 the first time we measured it. Second time it went to 50 volts at full OFF. I don't understand what you mean by "responding to miniscule leakage currents ... 'phantom' voltage readings." Are you saying that what we observed is an artifact of the measurement device, and that in fact there is no voltage flowing through the switch in the fully OFF position? That would be comforting in one sense about no safety hazard with the wiring beyond the switch, but disturbing in the sense of never being sure whether the voltmeter is accurate or not.
Any further elaboration/clarification you (or others) can provide would be appreciated.
Thanks.
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CWLee wrote:

No, if the bulb loads are connected to the output of the dimmer then my comments about phantom oltages are likely not relavent. It certainly does not sound like they are working properly if you see any voltage at all across the lamp loads when the toggle lever is moved to full OFF.
One thing you haven't revealed is justhow you are making your measurements.
What are you measuring the voltage with respect to? Specifically where are the two voltmeter leads connected when you make your measurements?
If the wall switch plates are in place is there a possibility that the plates are mechanically interfering with the toggle levers and keeping them from moving fully to their off positions?
It seems quite unlikely that TWO new dimmers would both be defective.
And even if the bulb filaments aren't producing any visible light with 40-50 volts across them they certainly will produce some heat. If you leave the toggle levers in their OFF position for several hours and then feel the bulbs, are they down at room temperature or can you feel some sensible heat.
More info from you will likely get us to the bottom of what's happening.
Jeff
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Jeffry Wisnia
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"No, if the bulb loads are connected to the output of the dimmer then my comments about phantom oltages are likely not relavent. It certainly does not sound like they are working properly if you see any voltage at all across the lamp loads when the toggle lever is moved to full OFF."
Perhaps I mislead you earlier; let me clarify. The reading of about 50 volts was not done with the bulbs as a load. The house circuit was wired to the switch, and then the leads from the voltmeter were attached to the output side of the switch. At the time the switch was not mounted to the housing, but rather suspended in air from the house wires. Then the toggle lever was moved and readings noted.
We have not tested to see if the bulbs are warm after several hours in the OFF position. That sounds like a good test, and we have considered it, and will eventually do it. Because of other wiring and construction going on in that part of the house, requiring that certain circuits remain shut down, it has not been practical to perform such a test yet. I'll keep you posted on any new developments. If the additional information provided in this post gives you further insight, please share it.
Thanks, and best regards.
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CWLee wrote:

<snipped my previous blatherings...>
I'd bet what's left of my virginity against a cigarette butt that if you make the voltage measurement you described WITH the bulb loads connected you'll see the voltage goes to zero when the slider is all the way down.
That 40-50 volts you measured was a "phantom" voltage developed by miniscule leakage currents, too low to even fry a mosquito, flowing through the megohms high input impedance of your voltmeter.
Capice?
Jeff
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It is _extremely_ misleading to measure the output voltage of a dimmer with a high impedance meter (eg: DVM) with no load (eg: a bulb) attached. Especially cheap DVMs. Even when a load is connected, it will be somewhat misleading.
A dimmer operates by chopping up the waveforms. Which means a lot of "off state", which can show as relatively high voltage unless it's loaded. Secondly, unless it's a true integrating DVM, voltage measurements are somewhat meaningless on chopped wave forms - even at full dim (but not quite off), the voltage seen by the load is still peaking at 160V.
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This may be too simple an idea but...
Sometimes the dimmer doesn't get really turned off. This is typically on "Preset" dimmers. Basically there are two controls, one dims the other turns it off. If the off part isn't obvious then lots of folks think it's off but it isn't.
I can't count how many slide or knob dimmers I've seen that aren't quite off.
RickR
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CWLee wrote:

I've read the various responses to date and they all have valid points. IFF you're still confused, here's a definitive test you can use that will verify whether the voltages are phantom or not.
With the same setup you've been using, measuring at the same place, find a way to put a resistive load across the two points where you're measuring. A standard light bulb will work fine. Place the light bulb or resistor connections across the points you are measuring. If the voltage drops to 0.0V, then it's phantom voltages and nothing to worry about in any way. If it doesn't drop to 0.0, then there is current available in the wires and something IS wrong, OR as another poster noted, it doesn't switch all the way off by design. If the voltage stays above, say, 30 V, then be VERY careful as there is a possibility that it's high enough to hurt you if you get across those wires! I'm going to suggest that won't happen; the voltage will go to 0.0 as you place the bulb across the connected meter probes.
A handy little gizmo that makes it easier to measure like this is one of those things you can screw a light bulb into and then plug it into a standard receptable. Available at most hw stores. It's easier to hook wires to the prongs of the device than to try to hold them against the bare bulb base and center piece. Also safer for you and for your wiring should you slip and it's not phantom voltages<g>. If you use a resistor instead of hte bulb, and have to buy one at RS or wherever, get one about 2k ohms. That meanst about 2,000 ohms. For safety sake, be CERTAIN to NEVER let more than one part of your body (hand) contact anything metal at any time. Don't even try it if there is any standing water around.
The other, probably simpler alternative, is to simply temporarily hook up the lights, turn the power on, and measure the same points. See what the voltages do then; I'm betting they'll go to 0.0 from around 120. It'd just about have to if the dimmer is working. This IS of course, a dimmer intended to dim flourescent lights, right? If it's incandescent only, then you also have the wrong type of dimmer.
HTH, Pop
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Pop` wrote:

<snipped>
Jeff
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Jeffry Wisnia
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The dimmers are NOT controlling fluorescent lights. They control incandescent lights.
Another bit of clarification, in case it makes a difference. These dimmer switches are not the kind with a sliding knob. These are the kind that, from 4+ feet away, look just like standard ON-OFF home wall switches.
Still puzzled, but with some good information and suggestions for further research.
Thanks.
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How about a make and model on these guys.
RickR
CWLee wrote:

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The original boxes have been trashed, but here is what I find on the switches themselves:
Leviton 6842 Dimmer
(It is possible that the number is 8842; very small print)
120 VAC 60 HZ Incandescent use only.
These were purchased from a local Home Depot on 5.30.06, and the ID info shown on the receipt, which may also be the UPC code, is:
07847769639 CS120 Ivory
Best regards,
Chuck Lee.
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I may have missed it but where were the voltage readings taken? Just for curious sake.
Hot to neutral or ground? Hot to switch leg in the switch box? Switch leg to neutral or ground?
If I am not mistaken: If you take a switch out of the wall and replace it with a dimmer. You may very well get a voltage reading of 50v, reading from the hot to the switch leg with the dimmer UNINSTALLED and the load still connected to the switchleg If the switch leg has the load tied into it your meter will definetly will see a differnce in potential.
Just curious.
On Fri, 6 Oct 2006 20:07:02 -0700, "CWLee"

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I'm unsophisticated in electrical terminology, but I'll try to tell you what we did so you can decide.
Picture two wires coming from the breaker box. One of these two wires was then connected to the input side of the dimmer switch. Then the digital voltmeter leads were attached to the other wire, and to the output side of the dimmer switch. No other load involved. Voltmeter set to read AC. As the toggle on the dimmer was moved from full ON slowly to full OFF the voltage shown on the voltmeter dropped slowly from around 120 volts ac to around 50 volts ac.
Make sense?
Thanks for sharing any insights you get from this.
Best regards,
Chuck Lee.
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DVMs should not be trusted to read the output of dimmers, _especially_ when there's no load on the dimmer.
DVMs have such high impedance, they can read phantom induced voltages off wires that aren't connected to anything.
If you attach the bulb to the dimmer too, you will get a somewhat more reliable reading.
Secondly, dimmers, as they get closer to the fully dimmed out state are generating a voltage waveform that's rather far away from a sine wave. Unless it's a very good quality DVM, it can display grossly misleading readings.
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I found a #6643 and a #6641 toggle dimmer which match your description closely, but no 6842 or other close variations.
Something a I should have mentioned earlier; Dimmers are suposed to have an "air gap" off, somewhere somehow. No ghost voltages no little glowing lights OFF!
Look for it! If you can't find it, take it back!
RickR
CWLee wrote:

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Mystery to me too. I have now taken a magnification glass and flashlight to the switch, and can confirm that the number is 6842. It is not printed, but "engraved" or perhaps stamped onto the metal.
Thanks again.
Best regards,
Chuck Lee.
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