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UPDATE: The plot thickens. I measured 2.5V at the door even with the wires completely disconnected from the transformer. So, the transformer is contributing to the voltage difference but not solely. What an adventure!

I'm going to call an electrician and will update this post when I learn more.


I have a doorbell transformer in my basement, about ~30 feet from my front door. The wiring in the walls may be longer than that, but I'd be surprised if it were significantly longer. I don't know much about the wiring. There's no chime box and there's only one doorbell in the house, but it's possible that there may have been other configurations in the past.

I attempted to install a Nest Hello video doorbell today and failed because I couldn't get the voltage at the door to measure more than ~12V using my multimeter.

Initially, I had a 16V 10VA transformer. At the transformer, I was able to measure ~19V and at the door, ~11V. I bought a new, 24V 20VA transformer. At the transformer, I measured ~29V and at the door, ~12V.

I tried restripping the wires on both ends for cleaner connections to minimal benefit, and now I'm out of ideas. I'm also puzzled by why the transformers have a slight difference in voltage at the door but not proportional to their difference in voltage stepdown.

Any ideas? I'd love to be able to fix this myself (or hire someone if that's what it takes), but I'm not going to open up the walls.

  • 1
    what voltage do you measure at the chime? – Jasen May 9 at 11:09
  • Those wires must go to china and back. That's a big voltage drop for no load on a wire.Check the wiring with a continuity tester, you have one on your multi meter. – JACK May 9 at 12:00
  • 2
    Are you sure that you're measuring the real voltage? Digital voltmeters are famous for reading "phantom" voltages on unconnected wires. What voltage do you read when the old doorbell is connected and working? – Daniel Griscom May 9 at 12:06
  • Unfortunately, there is no old doorbell to compare to. The multimeter is cheap and likely inaccurate, but I'm assuming it's precise and that relative measurements are correct. The ultimate test is plugging in the Nest Hello, and that worked just fine at the transformer but unfortunately didn't at the door. Is there anything I can do save ripping up the walls? – spitzanator May 10 at 17:15
  • 1
    I wonder if the doorbell was removed because of a problem , that or the chime coil is still in the circuit , that’s the only way I would think there would be that big of a drop. I thought the nest needed 30 va – Ed Beal May 12 at 22:50

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