Fix & Install

Doorbell Wiring Diagrams

Doorbell specific low-voltage wiring – 18/2 or 20/2  – can be purchased 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.

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.

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
Nutone 2 Note Door Chime

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 white or red wire (typical wire colors).
How to wire a doorbell with one button
Single Button Doorbell Wiring Diagram
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
Double Button Doorbell Wiring Diagram

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
NuTone / Broan C905K Doorbell Transformer
Related Topics : 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….

    1. Okay, that doesn’t make diagnosing any easier. Red wires at the chime, but not at any doorbell button.

      I’m not sure how comfortable you are with wiring and electricity, but I can assure you this doorbell chime and button combination is at the most basic level. These are not complex electronics you need to worry about damaging. You have very simple momentary switch types at the button and door chime. Which means instead of touching two wires together to complete the circuit, you have a switch plate that makes contact in the same way as touching two wires together when the doorbell button is pushed.

      Point being? You can play around with the wire configuration at the door chime without worry. The door chime is marked rear-trans-front to keep wiring organized just like the wires are colored for easy reference, but can be moved around like someone has done with your doorbell and chime and still work.

      As mentioned earlier, one of the red wires at the chime has to be 12-18v coming from the transformer. Always turn power off at the breaker box to be safe when working with wiring.
      • Connect one of the red wires to TRANS
      • Unwrap the white wires and connect one to the REAR terminal (Maybe they need to stay connected and have both connected to the REAR terminal). Hard to know without seeing and finding the transformer.

      Just keep swapping wire combinations at the door chime and hopefully you get both front and rear doorbell buttons working. That’s if those white wires actually lead to and connect the doorbell buttons. Could be cut somewhere and not connect to anything.

      Hope this helps and let me know if you’re successful.

  6. I have the exact 2 note door chime used in the illustration. The current wiring has four wires, 2/white and 2/red: the white wires are coupled together and not attached to the doorbell and each of the red wires are connected one to the front and one to the back doorbell terminals. The front doorbell functions properly, but the back doorbell does not ring. Do you have any suggestions on what needs to be done? Also, I have no idea where the transformer is located; the doorbell was installed when I moved to the house.

    1. Hi Robert,
      Wires are colored coded as a label and reference, but that doesn’t mean a previous installer kept to the standards, so locating the transformer would be very helpful to see what’s truly going on. The transformer shouldn’t be enclosed where you don’t have access. If you have a basement or crawl space, check the floor joists as shown in the transformer image. Another transformer location is near or inside (part of) the door chime itself.

      Do you have a transformer terminal on the door chime? I see no mention of a wire connected to a transformer, which means the transformer might be built-in?

      In the end, if all is fine with the wiring, you might just have a faulty rear door button.

    2. I have the exact 2 note door chime used in the illustration. The current wiring has four wires, 2/white and 2/red: the white wires are coupled together and not attached to the doorbell and each of the red wires are connected one to the front and one to the back doorbell terminals. The front doorbell functions properly, but the back doorbell does not ring. Do you have any suggestions on what needs to be done? Also, I have no idea where the transformer is located; the doorbell was installed when I moved to the house.

    3. If you’ve eliminated faulty parts from the equation, then it’s a simple wiring configuration issue. I’m assuming at some point a resident didn’t want the rear doorbell functioning for whatever reason, and just disconnected at the door chime and reconfigured the wiring; i.e. disconnected white wires and tied them together. Unfortunately, without seeing what’s connected at the transformer we’re just guessing though, so proceed with caution.

      NOTE: The door chime needs power to operate, and both the chime and doorbell buttons needs 12-16V power supplied otherwise they’ll overload and expire, so there has to be a transformer somewhere stepping the power down.

      Since the components aren’t polarity specific, and you don’t know where the transformer is, you can proceed to the trial and error phase without worry of damaging any parts. Obviously one of the red wires is powered from the transformer and the other red wire goes to the doorbell button? In the end one of those red wires should go to the transformer so you know it’s the powered wire.

      Can we take a step back? What color wires exist at the doorbell buttons?

  7. Installed a new transformer, primary and secondary connections are in place. Need to connect the low-voltage wires on the chime to the Trans and Front connectors, though low-voltage wires (both red) are unmarked from prior connection, therefore I have no way of knowing which is coming from the front door and which is from the transformer. Is there a way to test to determine which is the respective wire from each to connect in the chime box? Or can you offer any suggestions? Thank you!

    1. Hi,
      In this case you are dealing with low voltage and parts that shouldn’t suffer any issues if wires are swapped, besides not working. Connect one way, and if that doesn’t work, swap the wires.

  8. Just installed the Nutone doorbell shown above. The transformer is wrapped with a piece of yellow tape..
    I’ve followed the wiring instructions / transformer has power (AC) / wired correctly (I think) / but doesn’t work… does the tape on the transformer mean anything?
    Thanks Kevin.

    1. Hi Kevin,
      Some electricians, and others in the trades that do electrical work, may use electrical tape to cover the connections of a switch, or transformer in the situation, as a precaution to avoid terminals being touched and shorted out. Just a preference.

      Did you get the doorbell to work?

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