Quick question about light switch voltage

[hoyaguru]

I have a light switch that was crackling sometimes when I would turn the light on. Swapped out the switch today, and checked the voltage on it while it was switched off. It started out at 109 volts, and slowly went down until it hit 80 volts, and stayed there. I only have one other thing on this line, and it is another light switch for a different room. Tested that one the same way, and it stayed at 120 Volts, nice and steady. Checked a couple other light switches throughout the house, all were 120 volts. The stranger thing is, the 2nd light switch on the line that shows 120 volts is further down the line from the circuit panel.

Possible pertinent issues: The switch that goes down to 80 volts is connected to a ceiling fan, the fan is on a totally different circuit. Also, my whole house is aluminum wire, no idea why this might be an issue, but it was new to me when I bought this house 6 years ago, I'm used to all copper wire.

 

[littlespark]

Can I just point out the OP is in America. So will be looking for 110v not uk standard 230.

Can you tell us what you were using to test, and what points on the switch?
I assume a multimeter with 2 leads and you were testing between a hot terminal and ground?

Did the drop in voltage happen when the switch was on or off?

 

[hoyaguru]

Can I just point out the OP is in America. So will be looking for 110v not uk standard 230.

Can you tell us what you were using to test, and what points on the switch?
I assume a multimeter with 2 leads and you were testing between a hot terminal and ground?

Did the drop in voltage happen when the switch was on or off?

Yes, sorry, I am in America. Using an A. W. Sperry DM-4100A voltage meter, set to 500 ACV. It's what I use to see if a plug has power before working on it, or testing to make sure the power is on. Touching the leads on the two screws on the light switch that the wires are connected to. Every light switch in the house comes up as 120 volts, except this one, it starts out around 110 (though this varies) then slowly ticks down until it gets to about 80, then it sits there. This is the first plug from the circuit panel (unless they ran the power all the way to the garage and then back to this plug, which I guess is possible). As far as I can tell, there are only two light switches on this circuit, no plugs, and the other light switch on the circuit shows 120 volts when it is turned off and I touch the white and black wires.

 

[James]

Is it an led light? Or other low voltage fitting? If so then when measuring between hot and switched hot, it is not a surprise or a fault.

 

[Avo Mk8]

Measuring across the two terminals of a light switch when it's off is not truly measuring the mains voltage, although depending on what light bulb/load you have, and what the meter impedance is, it's often close!
What you are doing is putting your meter from live, in series with the load (a fan), to neutral.
If your fan has a capacitor in it, or maybe speed control electronics, it's putting an impedance in series with your meter, so you would expect a reduced voltage across the meter. It's also interacting with other stray capacitances in the wiring. (I can feel Lucien wincing, as this is a bit of a simplification?)

This is not a fault, it's just physics!

 

[hoyaguru]

Is it an led light? Or other low voltage fitting? If so then when measuring between hot and switched hot, it is not a surprise or a fault.

It's a ceiling fan light. Are you saying that this is a normal thing? I'm not in the habit of testing light switches, and had never seen this before, figured there was a problem. If this is a normal thing, then I guess I'll ignore it.

Measuring across the two terminals of a lightswitch is not truly measuring the mains voltage, although depending on what light bulb/load you have, and what the meter impedance is, it's often close!
What you are doing is putting your meter from live, in series with the load (a fan), to neutral.
If your fan has a capacitor in it, or maybe speed control electronics, it's putting an impedance in series with your meter, so you would expect a reduced voltage across the meter. It's also interacting with other stray capacitances in the wiring. (I can feel Lucien wincing, as this is a bit of a simplification?)

This is not a fault, it's just physics!

 

[hoyaguru]

It's a ceiling fan light. Are you saying that this is a normal thing? I'm not in the habit of testing light switches, and had never seen this before, figured there was a problem. If this is a normal thing, then I guess I'll ignore it.

It's a ceiling fan light. Are you saying that this is a normal thing? I'm not in the habit of testing light switches, and had never seen this before, figured there was a problem. If this is a normal thing, then I guess I'll ignore it.

It's a ceiling fan light. Are you saying that this is a normal thing? I'm not in the habit of testing light switches, and had never seen this before, figured there was a problem. If this is a normal thing, then I guess I'll ignore it.

Wow, triple post!. Just wondering, if this is a normal thing, why are all my other light switches showing at 120 volts? If I turn the light on, it shows 0 volts, if I turn the light off, then I'm seeing the voltage. This switch is for a ceiling fan light, but the fan itself is on a separate circuit, I can turn off the circuit for the light and still use the fan. If this is just a dumb question, please let me know, it was just something I noticed today when I changed the light switch.

 

[Avo Mk8]

Hi
If I remember correctly, there is legislation in the USA to limit the maximum wattage of bulbs in a ceiling fan.
So manufacturers fit a power limiting device in the bulb circuit of fans (called a wattage limiter)
I think this gadget when in circuit with your meter is giving the reduced (and changing) reading.
If you have a more recent fan it may have LED bulbs, which again could give a different meter reading from your other lights.

So to be clear, the circuit you create when measuring the fan light is different from the circuit in play when you measure other lights.
If you want to measure mains voltage - measure between hot and neutral (except there may not be a neutral wire at the light switch)

 

[hoyaguru]

Hi
If I remember correctly, there is legislation in the USA to limit the maximum wattage of bulbs in a ceiling fan.
So manufacturers fit a power limiting device in the bulb circuit of fans (called a wattage limiter)
I think this gadget when in circuit with your meter is giving the reduced (and changing) reading.
If you have a more recent fan it may have LED bulbs, which again could give a different meter reading from your other lights.

So to be clear, the circuit you create when measuring the fan light is different from the circuit in play when you measure other lights.
If you want to measure mains voltage - measure between hot and neutral (except there may not be a neutral wire at the light switch)

Wow, thanks for the info, I would have never figured this one out. Glad it's not something that I'd need to call a real electrician out for.