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Doorbell Wiring Diagrams

Nutone 2 Note Door Chime
Nutone 2 Note Door Chime

The following doorbell wiring diagrams utilize a NuTone® 2 note doorbell / chime, but the schematics are common practice and should apply to many, if not all brands of doorbell wiring.

Standard low-voltage 18/2 or 20/2  (gauge / # of wires) listed for  doorbell wiring use can be purchased at any home improvement store.

CAUTION: ELECTRICAL HAZARD: Turn off all power at fuse or breaker box before working.

SEE ALSO: How to Secure Doorbell Wires

If there is no existing doorbell wire and/or adding wire seems like a difficult process, a wireless door chime may be a better solution.

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 manufacturers instructions. Either terminal can be mounted to the white or red wire (typical wire colors).

Single Doorbell Button Wiring


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 (typcial wire colors).

Double Doorbell Button and Chime Wiring


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?
  • If an application is to connect two, 2 note chimes together, will 2 transformers be required?
Find Answers @ NuTone


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 (as shown), or fit into a single gang box like a switch, e.g. NuTone C915.

Junction Box Mounting: 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 Junction Box Mounted Doorbell Transformer


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  1. 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!

    • 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.

  2. 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.

    • 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?

    • Hi Dan,
      Without knowing and seeing the existing combination, I’m uncertain as to what directions you require. Maybe this site will give you the answer you need if you can find the brand and model #.

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