I'm confused - the arrows in this picture of a doorbell transformer range from 8V - 24V with arrows pointing just about everywhere.

I think I need to buy this to get enough power to a Nest doorbell. If I install this, how do I get 24V instead of 8V for example.

Heath Zenith SL-125-02 Wired Door Chime Transformer

Image: Heath Zenith SL-125-02 Wired Door Chime Transformer

  • 11
    Right and left for 24. Right and Centre for 16. Left and Centre for 8.
    – crip659
    Dec 1, 2021 at 23:40
  • What does the nest doorbell call for? How many volts/amps and AC or DC power. Check before buying.
    – crip659
    Dec 2, 2021 at 1:10
  • Crip clarified. I get how this works now.
    – ThisClark
    Dec 2, 2021 at 4:27
  • The Nest doorbell is some kind of smart device? Is it ok with getting unregulated AC? Normally you wouldn't buy a naked transformer, you would buy a power supply.
    – AndreKR
    Dec 2, 2021 at 14:55
  • My current doorbell is wired into a 10V transformer. The wired Nest doorbell will require 16V-24V. The power and voltage requirements for the Nest doorbell can be found here: support.google.com/googlenest/answer/9247132?hl=en
    – ThisClark
    Dec 2, 2021 at 17:28

1 Answer 1


The arrows point to the screws that will give a specific voltage and amps.

For 24 volts at 20VA you use the right and left screws. Centre screw is left empty/unused.

For 16 volts at 10VA you use the right and centre screws.

For 8 volts at 10VA you use the left and centre screws.

  • 1
    Additionally, this can be tested using a common digital multimeter, an exceptionally useful tool for specific tasks like this. Strongly recommend adding a cheap $10-$20 meter to one's toolkit.
    – Criggie
    Dec 2, 2021 at 21:48
  • Unloaded the voltage is likely to read a little high, but that shouldn't be a problem. For the Nest, if you're worried, you could use the 16V pair as that's also within spec
    – Chris H
    Dec 3, 2021 at 8:07

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