Understanding the power to my door bell

Hi guys,

I would like to understand how my outside door bell light works.

Based on what I understand (the outside wire) it's one wire getting interrupted & when pressing the door bell it creates contact resulting in the inside door chime to move and make ding dung sound.

But how does the actual light outside on the bell light up since it's one wire (I.e. Positive wire)? As well as when I measure the voltage on the wire itself I'm getting 24V.

How is that possible I would like to understand that.

Same thing with my thermostat wire, when I measure the voltage I'm getting 24 volts but based on my understanding it's one wire making contact when requesting for heat. (It's heat only zone) so how come I'm getting 24 volts

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@abrahamyaris that should be an AC circuit so no positive wire. What voltage do you get when you measure AC? That is a really interesting question :-)


I'm getting 24vac when I'm putting my multimeter on each of the door bell wires.


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@abrahamyaris , Abraham, are you sure your door bell button only has one wire, I have not seen this before. Check link below as this is what I have always seen for low voltage door bells with a transformer. Normally a lighted button will always be on because the bulb circuit is complete until you press the button. When you press the button it breaks contact with the button/bulb(button light goes out) and this is where the bell contacts come into play, while button pushed the bell rings because the second contacts in button assembly are being used, but there is no light on the button because the internal contact to the button light is broken.

I hope this explains it OK, Good luck.

I hope this helped you out, if so let me know by pressing the helpful button.


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How is the light on the bell lightened up?

Doesn't a bulb need to have positive & Negative In order to light up?

The wire that comes from the transformer to the button only provides one I.E. Positive (& than it travelers to the chime when the button is pressed)


@lpfaff1 @abrahamyaris do not forget that this is an AC circuit, same with your thermostat. Let's not focus on the light but on the fact that you measure 24V on the wires of the doorbell switch. I have a couple AC transformers and will see if I can prove it tomorrow so stand by ;-)


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Here is how the light stays on when the switch is in the open position ....


Look down about 3/4 of the way down the page to see the diagram of a typical lighted doorbell switch.

stupid "dead-the-next-week" hyperlinks - HERE:

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Abraham Yaris will be eternally grateful.
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