How-To

Doorbell Wiring Diagrams

Learn about every aspect of a low-voltage wired doorbell system; from how each component works and how they connect in various doorbell configurations.

The following doorbell wiring information focuses on combination doorbells (front and rear chime in a combined unit) and uses Broan-Nutone, more specifically the NuTone doorbell parts as reference. These are just the products we chose to work with, but the provided wiring diagrams and in-depth description of parts is universal, and should apply to all brands of low-voltage wired combination doorbells.

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Applies to All Wired Doorbell Systems

  • Doorbell push buttons don’t have a positive and negative. Either terminal of the push button can be mounted to the red or white wires shown in the diagram (ref. doorbell parts section below for more information).
  • The output side of the transformer doesn’t have positive and negative terminals. The red wire shown in the diagrams can connect to either terminal of the transformer and push button (ref. doorbell parts section below for more information).
  • Annunciator(Bell) wire vs. Thermostat wire? Either is fine. Bell wire comes as separate individual wires, while thermostat wire has a jacket to keep the wires bundled together. Depending on the layout of your home and location of doorbell components, choose if individual or bundled wires work better (ref. single doorbell button wiring diagram).
  • WARNING: Electrical Hazard. Before beginning work, turn power off at the breaker panel or fuse box to avoid injury. For safe wiring practices, consult the National Electrical Code® and your local building inspector, or licensed electrician.

Wiring a Single Doorbell Chime With a Single Button

  • The NuTone C905 has a rating of 16V – 10VA; these are standard specs for most single 2-note chimes. This is the transformer supplied in contractor grade wired door chime kits.
  • The same wiring diagram applies to a single bell or buzzer (non-combination chime). Ignore the rear terminal.

How to wire a single chime and doorbell button

*Pre-packaged Bell Wire AWG varies per manufacturer and reseller. When purchasing, note that the wire’s max volt rating complies with the transformer output voltage.
Items Needed Specifications Purchase
Doorbell Button Basic or Lighted
NuTone C905 Transformer or Equivalent 16-volt, 10VA
*20 gauge 2 conductor Wire (20/2) Sold By-the-Foot or Roll
*18 gauge 2 conductor Wire (18/2) Sold By-the-Foot or Roll
Complete Door Chime Kit Wire not included

Wiring a Single Doorbell Chime With Multiple Buttons

  • Using the majority of wiring information for a single chime and doorbell button; add a rear, side, or garage entry door button in addition to the main front entry door button.
  • The rear is only a 1-note chime. You’ll notice a bumper (ref. image in chime parts section below) inside the chime – above the “rear” chime pin – that prevents the top chime bar from being activated; creating a slightly different sound between the front and rear buttons to indicate which button is being triggered.

How to wire a single chime and double doorbell button

Wiring Multiple Doorbell Chimes With a Single Doorbell Button

  • Strategically placing two or more chimes assures that you hear the doorbell sound throughout the entire home.
  • Powering 2 chimes simultaneously requires a larger transformer, e.g. NuTone C907 with a rating of 16V – 30VA.

How to wire a double chime and single doorbell button

Wiring Multiple Doorbell Chimes With Multiple Buttons

  • Using the majority of wiring information for a double chime and single doorbell button; add a rear, side, or garage entry door button in addition to the main front entry door button.
  • The rear is only a 1-note chime. You’ll notice a bumper (ref. image in chime parts section below) inside the chime – above the “rear” chime pin – that prevents the top chime bar from being activated; creating a slightly different sound between the front and rear buttons to indicate which button is being triggered.

How to wire a double chime and double doorbell button

Common NuTone Door Chime FAQ’s
We wanted to cover the basics and more in this article, but for more answers about NuTone products, reference the Nutone faq page.

Example questions with answers, include:

  • Can a 2-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 2-note chime that does not ring loud enough?
  • If an application is to connect two, 2 note chimes together, will 2 transformers be required?
  • What is occurring if the chime rings by itself?

**Consult your specific doorbell brand for further questions.

Understanding Each Part of a Wired Doorbell System

There are three main stages of a wired doorbell system, plus the wiring to connect all the components.

1) Doorbell (Chime): You can’t have a ding-dong sound without the heart of the doorbell system. There are varying decorative chime covers, and dimensions may vary between manufacturers, but the fundamental chime design you see here, by NuTone, will remain uniform.

Nutone 2-note wired chime

To access the internal chime, most, if not all covers snap on. To remove – pull forward.

2) Push-Button: The buttons used to activate the chime are of the momentary switch type. Think of it like this, you could remove the switch and manually touch the two open ended wires together, therefore completing the electrical path to activate the chime. Add the switch, and it achieves the exact same thing, momentarily completing the electrical path when depressed to energize the chime, then breaking the electrical path when released as the internal contacts no longer join.

Doorbell pushbuttons are not polarity specific, therefore either wire can connect to either terminal.

A common rectangle pushbutton is included in many chime kits, but you can upgrade to another pushbutton, including LED buttons, and the wiring will remain the same.

NuTone doorbell pushbutton

3) Transformer: A step-down transformer reduces the 110-120VAC line voltage down to 16-20-24 low-voltage for doorbell component compatibility.

As noted in the wiring diagrams; depending on the door chime, or having multiple chimes, the transformer specs need to comply for chime function.

*Find more Nutone transformer specs and the latest information at NuTone.
Model (link) Mounting Type Rating Purchase
NuTone C905 lock-mount or wall-mount 16-volt, 10VA
NuTone C907 lock-mount or wall-mount 16-volt, 30VA
NuTone C909 Tri-volt lock-mount or wall-mount 8, 16 or 24-volt 20VA
NuTone C915 Fits in single electrical box 16-volt, 10VA

Locating or Installing a Transformer:

  • A transformer can be mounted inside a junction box, e.g. NuTone C915, which may reside directly behind the door chime. This setup can remove the guesswork of locating a remote mounted transformer.
  • A transformer can be mounted to the outside of an electrical junction box (ref. transformer image gallery). Check basements, crawl spaces and attics for possible locations.
  • Most transformers have screw mount plates as well as the electrical box connector. Check open floor joists or wall studs in the basement, crawl space and attic.
Quick Tip
Essential Electrical Tools
*Check local home improvement and electrical supply stores for product availability.
Product Description Purchase
Wire Strippers & Cutters Choose a wire stripper that best fits your needs: Wire Stripper & Cutter, Multi-tasking Wire Stripper (shown), or a Pliers with Wire Stripper.
Screwdrivers Choose individual screwdrivers or save space and money with a capable multi-bit screwdriver. The Klein 11-in-1 with Combo Screw Tips (32505) is a great choice for any homeowners electrical projects.
Twist Wire Connectors Twist wire connectors make wire connections easy (eliminate pre-twisting) and have a broader range per connector than basic wire connectors; thus reducing the amount of different sizes of wire connectors needed.
Specialty Wire Connectors Use weatherproof wire connectors with pre-installed silicone for exterior wiring projects. A wire too short? A splice connector easily solves the problem.
Voltage Testers A non-contact voltage tester will detect the presence of AC electricity, while an AC/DC voltage tester offers a few more functions: LCD readout, no batteries needed for voltage detection, test continuity, and some detectors have a GFCI trip, .
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