Fix & Install

Doorbell Wiring Diagrams

Solid copper (not stranded) low-voltage wiring (18/2 thru 22/2) can be found at any local home improvement store.

ELECTRICAL HAZARD: Turn off all power at breaker panel or fuse box before working to avoid electrical shock.

Learn how to properly secure low voltage doorbell wires to avoid component malfunctions – read article.

NuTone door chime and transformer FAQ…

  • Can a two-note chime be replaced by a 4- or 8-note chime?
  • May two-chimes be on the same pushbutton?
  • What can be done for a two (2) note chime that does not ring loud enough?
  • What is occurring if the chime rings by itself?

Find many more common questions and answers @ NuTone

Nutone 2 Note Door Chime

NOTE: The following wiring diagrams cover the Nutone 2 Note Door Chime, but this common wiring configuration should pertain to all other brands of chimes as well. Please consult your specific brand of chime for reference.

Single Button Doorbell Wiring Instructions

  • For single button activation, a common transformer is the NuTone C905 (see below). Rating = 16VAC, 10VA (watts).
  • Neither door buttons nor transformer are polarity specific, unless otherwise noted in manufacturer’s instructions. Either terminal can be mounted to the red or white bell wire (typical wire colors).
How to wire a doorbell with one button
Wiring Too Difficult? Try a Wireless Doorbell.
Available at Amazon >

Double Button Doorbell Wiring Instructions

  • Diagram for FRONT and REAR door buttons.
  • Use NuTone C907 transformer. Rating = 16VAC, 30VA (watts). Extra watts = extra power = adequate chime  sound, when longer runs of wire on two button applications is typical.
  • Neither door buttons nor transformer are polarity specific, unless otherwise noted in manufacturers instructions. Either terminal can be mounted to the white or red wire (typical wire colors).
Front and rear doorbell wiring diagrams

What’s a Transformer and its Purpose for Doorbell Installation?

A wired doorbell needs power to operate, but the 120VAC from the electrical box is too powerful and un-needed for the application. A transformer steps the 120VAC voltage down to 16-20-24 volts to be compatible with doorbell components voltage ratings.

A transformer can be located inside the bell or chime enclosure, mounted to a junction box as a separate unit, or fit into a single gang box like a switch, e.g. NuTone C915.

Junction Box Mounting (as shown): The transformer will have males threads and a nut; allowing the transformer to mount via one of the junction box knockouts. Power will be delivered from the 120v wires inside the box; connecting to the pigtail wires pre-attached to the doorbell transformer.

*Further specific instructions will be included in product packaging.

NuTone / Broan C905K Doorbell Transformer
Tags : doorbellelectrical


  1. I”m trying to figure out why my new Ring Pro video doorbell won’t sound the mechanical chime while the old Ring doorbell, which I’m told uses much less power, did and my regular doorbell works as well. Tech support is trying to help me, but I think the issue comes down to how my mechanical doorbell is wired. Here are the facts:

    1. Looks like a Nu-tone chime from the mid-80’s.
    2. Has two red wires leading to standard terminals labeled “front” and “transformer”.
    3. I took a voltage meter to the red wires and dectected only trace voltage.
    4. At the chime but simply tied together with a wire nut are two white wires.
    5. I stuck one probe from my voltage meter into the wire nut and the other end to one of the red wires on the chime and got a 19 v reading.

    Is this wiring unusual and does it at all explain why I can’t power the power hungry Pro doorbell?

    Thanks! – Rob

    1. Hi Rob,
      I apologize, but as of now we haven’t yet tested the Ring Pro Video doorbell. and therefore have no hands-on experience to offer much for diagnostics help.

      Do you know where your doorbell transformer is and the rating of it? Maybe the new Ring doorbell requires a higher powered -output- transformer, like the NuTone C907 mentioned in the double doorbell diagram.

  2. I just replaced my wired door bell servicing both front and back doors. The three wire coming from the bell is coloured (black, red, and white), but the wires from the buttons and transformer are all one colour (brown) so it is a bit confusing. In any case, once I had it all connected, I ended up with the ding dong at the back door, but I want the ding dong at my front door. When I switch the wires at the bell I only get a dong at both the front and the back doors. I am no electrician so I am puzzled why this is so and wonder how I get the ding dong at my front door. Any advice on this?

    1. Hi Mel,
      If your doorbell, transformer, and push buttons are all accessible, I can only recommend following the diagrams shown. I know you may be thinking “great…thanks for nothing”, but there isn’t much else to add. Unfortunately past installers can create chaos and the best answer is to redo what is existing from scratch.

    2. Unfortunately, The wires are not accessible, but all are gathered to one place that is accessible. Power appears to be delivered okay through the system. Except I need the ding dong and dong interchanged. Any suggestions what I might try? And why doesn’t just exchanging the wires at the bell work to do this? One observation – I don’t know for certain which wires go where, but I have based my best guess on following the wires as far as I could.

    3. Mel,
      As you mentioned “I don’t know for certain which wires go where”. Therein lies the problem. Who knows what connections, splits, etc. exist. To my knowledge, all basic door chimes aren’t polarity specific, and you are working with low voltage, so at your own risk, you should be able to play musical chairs with the wires until you sort out the right wiring configuration. I’m not sure if the same holds true for electronic chimes.

  3. I have a door bell chime from the late seventies i removed it to di renos i have four wires from the wall and only three spots to put the there was two wires together how do i connect these wires

    1. Denise,
      The wires coming out of the wall could be connected in numerous ways. There is no sure way to tell unless you follow them from point A to B, then follow the diagrams shown to make sure all is wired properly.

  4. Doorbell installation: I purchased a #0050500 Transformer and a UT-7580 Doorbell after installing the transformer and the doorbell according the instruction, but only the chime for the front door will work I cannot get the back door to ring when I switch the wiring from the back termnial to the front termnial then the front push button will ring the back door sound, I can only get the back door button to work when the front door button wire is clamp together there are four red wire and four white wire running from transformer to the chime but the chime only have three termnials front, rear, and trans. for the red wire there is no termnial for the white wire.
    Can you help me with this problem?

    1. Hi Eli,
      I’ll try and help but many of these projects are hard to sort out without some type of visual. Looking at the UT-7580 Doorbell installation manual, it appears to be the same configuration as the instructions shown in this post, which has me wondering why you have so many wires? You said there are 4 red and 4 white? Something is obviously getting crossed up along the way.

    2. Hello,
      Thank you very much for looking into the matter, the mfg. tech. seem to think that there is a posibility that the wire might be crossup.

      Thanks again,


    3. I agree with the manufacturer tech. If all parts are installed properly and there is an issue, then product defectiveness may be the issue, but most times there is an error in the installation and / or compatibility. Wiring can be very tricky when swapping out parts as you never know what is going on behind the scenes with the actual wiring. Always best to make sure you can trace the entire wire – from part to part – and confirm all is right.

  5. Hi Team – I am wiring a new Vivint doorbell to replace my existing, but, this is a bit of a long story. I took off my bell box, and clamped the wiring into my wall, and painted over the hole in the wall. I then took my wiring from the door bell, and tucked in down near the door frame. (I was going to get a wireless doorbell, hence removing the equipment)…….

    Now, I have this new cool Vivint doorbell that Z-Waves into our system, but, it requires a power feed at the door, i.e. the actual doorbell wiring. I know that the hot leg comes from the basement transformer, and the neutral from that same transformer routes to where the original bell box used to be…

    My question is, how easy is it to take the front door bell wiring, and run a straight shot pair (red/white) directly from the transformer to the front door, where the new equipment is? Remember, the front door bell only needs power.

    1. Hi John,
      How easy? That varies based on many circumstances and a touch of luck. Our home has conduit installed for electrical, so I have a smooth pathway up the wall and to the doorbell button, then a full open basement where the wires lead to the exposed transformer. Point being? This is a very simple situation if I were to need new wires. Not sure how your situation compares?

      Doorbell buttons are mostly on exterior walls so you may have insulation to contend with. A very common device to use is a fish tape when trying to pull new wires. They’re flexible, yet stiff enough to push through minor obstacles without bending. You may be able to rent one at a Home Depot or other local rental places that carry tools.

    2. I just had my security company here tonight, and, they used the fish wire device, simple. I also traced my basement transformer wiring to where they pair off… I just might be able to join the two pairs that lead to bell box at the same position as splicing the hot and neutral…

      A work in progress….

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