Where is the power to my doorbell coming from?

[MattinCA]

Replacing the receptacle in my1950s house with no ground. While I was at it, I wanted to remove the old doorbell we no longer use and its transformer but when I disconnect the transformer from the power, my NCVT still indicates the small red and white wires are energized. If not clear, the black and white wires with the nuts had pigtails going to the bare black wires in front of the transformer.

There are doorbell buttons at both the front and side doors. The terminals with the red wires on the doorbell are marked "bell" and "chime" on the other side. We never used the side doorbell button; the front one just made a sort of clunking sound. I assume the front doorbell button sounds the "bell" and the side doorbell button sounds the "chime" or vice versa. So I figured the same source that powers the receptacle sends 115V to the transformer, which drops it to 10V and sends 10V on two switch loops on the white wires to the front and side doorbell buttons, which then return the power to the doorbell via the red wires depending on which button is pushed.

So I cannot figure out why my NCVT indicates power in the small red and white wires when the transformer is disconnected from power and even when the circuit is turned off at the panel. I thought I could just snip the (presumably dead) small red and white wires and tuck them away in the box but I don't want to do that if they have power, even 10V.

 

[Snoonyb]

NCVT's are proximate devices, so if the circuit feeding the power to the pictured box is shut off at the breaker, you may have a 2nd transformer powered by another circuit.

So disconnect the reds from the transformer secondary, P/U a VOM, VOLT, OHM METER, start checking voltages.

 

[PJB12]

Hello MattinCA,
Does NCVT mean non-contact, as in sniffer?

If so, quite often the ones that can detect low voltages (such as 10 volts) are so sensitive that they will pick up tiny, stray eddy currents from wires that pass near the doorbell wiring and is induced into the door bell wires. The neighboring wire may be in a wall somewhere.

Other sources can trigger them too. I had a Fluke that was so sensitive it picked up current from my body. I had a Klein that would alert with the slightest move of my hand.

For anything under 50 volts, sniffers can be kind of troublesome. It would be a more certain test with the volt meter Soonyb mentioned above.

Semi-Related: If you want the chime that only clunks to operate, first inspect the rubber grommets that hold the bar which the solenoid plunger hits. Inspect the end of the plunger to be sure the (usually plastic) tip didn't break off. Finally, pull the plunger up and clean it with naphtha.

Paul

 

[jik lower]

Replacing the receptacle in my1950s house with no ground. While I was at it, I wanted to remove the old doorbell we no longer use and its transformer but when I disconnect the transformer from the power, my NCVT still indicates the small red and white wires are energized. If not clear, the black and white wires with the nuts had pigtails going to the bare black wires in front of the transformer.

There are doorbell buttons at both the front and side doors. The terminals with the red wires on the doorbell are marked "bell" and "chime" on the other side. We never used the side doorbell button; the front one just made a sort of clunking sound. I assume the front doorbell button sounds the "bell" and the side doorbell button sounds the "chime" or vice versa. So I figured the same source that powers the receptacle sends 115V to the transformer, which drops it to 10V and sends 10V on two switch loops on the white wires to the front and side doorbell buttons, which then return the power to the doorbell via the red wires depending on which button is pushed.

So I cannot figure out why my NCVT indicates power in the small red and white wires when the transformer is disconnected from power and even when the circuit is turned off at the panel. I thought I could just snip the (presumably dead) small red and white wires and tuck them away in the box but I don't want to do that if they have power, even 10V.

If your NCVT is still indicating power in the small red and white wires after disconnecting the transformer, it’s likely due to phantom voltage. This can happen when there is a capacitive coupling between the wires, especially in older systems. The wires might not have any real current running through them, but the voltage is being picked up by the non-contact voltage tester (NCVT) because of the nearby live wires. To be sure, you can use a multimeter to check for actual voltage or current in those wires. If the multimeter shows no real voltage, you can safely disconnect and tuck them away. However, if you're uncertain, it's always best to have an electrician inspect it to ensure everything is properly disconnected and safe.

 

[MattinCA]

My digital multimeter showed 0 voltage from the red and white wires after the transformer was disconnected from the power even while the NCVT lit up. My meter has 2 ACV settings--200 and 750--so I used the 200V setting. I don't know if that setting is not sensitive enough to pick up 10V but it's the meter's lowest setting. It showed 115V on the receptacle so I know it works lol. If the 200V setting is sensitive enough to pick up 10V if it's there, then I will trust that the 0V reading is accurate and stop worrying about it. I could reconnect the transformer and chime; verify that the meter shows 10V on them, then disconnect the power from the transformer and verify 0V, but I am not quite that anal.

 

[PJB12]

My digital multimeter showed 0 voltage from the red and white wires after the transformer was disconnected from the power even while the NCVT lit up. My meter has 2 ACV settings--200 and 750--so I used the 200V setting. I don't know if that setting is not sensitive enough to pick up 10V but it's the meter's lowest setting. It showed 115V on the receptacle so I know it works lol. If the 200V setting is sensitive enough to pick up 10V if it's there, then I will trust that the 0V reading is accurate and stop worrying about it. I could reconnect the transformer and chime; verify that the meter shows 10V on them, then disconnect the power from the transformer and verify 0V, but I am not quite that anal.

If it is a digital meter, set to 200 volts AC, the meter should certainly pick up ten volts. To be sure it does, read across the transformer with nothing hooked to the secondary to find if you see the ten volts.

You can even try this- Turn on the meter set at 200 AC. Hold the probes apart. Do you see millivolt readings bouncing around? If so, you know that your meter will pick up the ten volts.

If the meter is analog, reading low voltages will depend on the meter.

The non-contact sniffer detection was certainly reading what I wrote in #3 about. (Induced voltage from nearby wires tricking the sniffer). It could be quite low- even micro-voltages can trigger some sniffers like my Fluke sniffer.

Paul

 

[MattinCA]

Thanks, y'all.