My friend sent me a photograph of this transformer, which is installed above the main breaker panel, with leads running from the panel into the transformer. The stamped labels read

  • PRI. Volts: 110
  • SEC. Volts: 24
  • CYCLES 60

However, the leads out from the transformer disappear into the ceiling (so either to some unknown device or terminated somewhere). The house was built in the 1960's and we believe the device to be from time of construction.

Does anyone know what this might be for?

Edwards Transformer

4 Answers 4


My guess would be the doorbell or an intercomm system. Something like that. The original heating system might have needed 24 volts.

Disconnect it and see what does not work.

  • I had considered telling him to do just that (disconnect it and see what breaks) but it might be something more important than a doorbell. Also, why would a doorbell transformer be above the breaker panel instead of housed within the the bell?
    – msanford
    Commented Nov 14, 2011 at 5:08
  • 8
    I have 2 houses and both of them have the doorbell transformer in a utility colset. They are not part of the bell. Edwards still makes signaling (doorbell) transformers so I'm sticking with my first guess. :) Commented Nov 14, 2011 at 5:15
  • 5
    Unless the house has a generator fail-over from the same era, it can't be so critical that a brief disconnect would cause problems. Testing the doorbell would take about a minute. Doorbell was also going to be my suggestion, and it's also Google's (when searching "edwards 24v transformer" at any rate).
    – Scivitri
    Commented Nov 14, 2011 at 7:41
  • Disconnect it and see what does not work is always sound advice BTW. Commented Apr 2, 2012 at 1:07

My first guess would be "doorbell" since my house's installation uses a 24V external transformer as well.

My second guess would be an electrically supplied smoke detector. Ours, and I suspect most, run off 110V, it's possible that some older model may have used 24V.


This is most certainly a Doorbell/Intercom transformer from the company Edwards Signaling. I work in the Intercom industry and the name is pretty well known, although this particular model is before my time - so I cant be sure exactly what its for. If you can find a model # I can do a bit of research for you.


No doubt it's a doorbell transformer. The primary is fed from the breaker box 120VAC into it and the secondary is 24VAC which is perfect for a doorbell. Cycles is 60 meaning 60Hz. I would take a voltmeter set to AC and check to see if you actually get 24VAC out of it. The white wire should be considered the neutral and black the 24VAC hot lead. This transformer or one that behaves just like it can still be purchased at Home Depot, or HVAC supply house. I can't read the VA Volt-Amps but to find the amps take the VA number and divide it by 24 and you can find the amp rating of the transformer. This same voltage is found in today's central AC systems but I doubt that was available for a house this age. I would make sure you have a fuse on the black primary wire leading into the transformer if you decide to keep this setup. A simple inline 3A fuse rated at 250VAC would be fine; if you plan on keeping this installed, better to make it safe.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.