I moved into a new home and have a doorbell transformer that is reading 16V at the transformer itself and on the wires coming right out of the transformer. The wires, though, are only showing ~7.5V at the site of the doorbell after they travel from the transformer to the doorbell. Both the transformer and wires are likely pretty old (wires have the old string/cloth covering).

I've checked for a solid connection, which we have. Any idea what the likely culprit is? Is it possible that the natural resistance of the wire is causing the drop? (I don't think so but just wondering...). I can access the wire in our attic for most of its run and it appears to be fine and intact, so I'm having a hard time figuring out why the voltage would drop so much. Would love any advice on what it might be or how to troubleshoot before I go to the trouble of trying to replace the wire entirely.


  • isolate the wires coming out of the wall at door bell. it is usually there where they touch
    – Ruskes
    Jul 16 at 22:57
  • 1
    Resistance should not be a factor unless you are using hundreds of feet of wire. Corroded connections can be a factor.
    – crip659
    Jul 16 at 23:04
  • is the transformer getting to hot to touch
    – Ruskes
    Jul 17 at 1:52
  • 1
    Have you altered the wiring of the switchloop the goes to the pushbutton switch so that you are reading transformer only voltage, or are you reading the open circuit voltage through the coil of the strike actuator? Jul 17 at 13:54

1 Answer 1


Most probable root case:

The wires at the door bell side are heavily oxidized, not giving good contact to your volt meter, thus showing only 7.5 Volt

Usuly the door bell wires are exposed to outdoor elemnts.

They can oxidize (giving you bad contact). Use some sand paper and make them shine.

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