Electrical Wiring in the Home/Door bell transformer wiring


QUESTION: We have three door bells all connected to one transformer and one chime.  Two door bells have two wires and one has 3 wires going to it but only 2 are connected.  The chime works (barely) with the two two wire bells but not at all with the three wire one. How should they be properly connected (to the transformer) and to the chime?  Thank you.

ANSWER: Phil,  is this a new problem?  Or is this a home you just purchased or moved into?  I need to know if I looking for a fault or a system installed improperly from the beginning,

Be prepared,  if you did not install this system, you have no way to know what someone did before you and NEVER trust what someone did before you as being correct  ON ANYTHING.

Next there are many variations of chimes, bells, transformers and buttons,  and there is not just one simple answer to your question,   but I have provided about everything you will need to check,   I really need to know if the three system worked adequately before,   one switch, one connection to anything, transformer, chime, can cause a voltage drop that takes some doing to locate.  

At the end I put a new install instruction sheet for you to look at,

Another site with some very simple diagnostic tests in a tree format is  thecircuitdetective.com   you might want to read his diagnostic tree, which includes door bells prior to starting this project  

Plan on having a helper, and if possible a volt meter or power tester,  you can get a decent VOM    volt ohm meter at most hardware stores for about $6.00  it has scales to measure voltage,  AC and DC,   simply set it to voltage,  prove your primary voltage,   [the normal house voltage around 115  is connected to the primary side of the transformer,  if that voltage is low for whatever reason, the more load or bells or buttons become even more of load due to the problem with the incoming power,        start at the beginning so your know!

Next consideration    the size  [amount of POWER supplied from the main transformer has to be large enough to operate the three switches]

For example, you have a system of indicator lights,   and each light is located in a different area of the house,      

All are connected to ONE Switch and one power supply.

Each bell or chime unit, has a power rating,  just like a light bulb,    including the wire size!

Because I have no idea if the system worked prior to this, or not,  are we repairing or correcting something someone did in front of you that NEVER WORKED AND NEVER WILL?

So your power supply is wired to 3 push buttons,  the indicator lights are each wired In parallel to the power supply,       you have three  25 watt indicator lamps,    but you have a 50 watt power supply,    two of the lights would work,  if wired,  but add the third and 50 watts cannot supply enough power for that third light.

It could be the power supply or transformer in this case, is just not large enough to run three chimes,  [again I have no idea if they every worked all together]

It could be the size  {AWG] of the wire, and the length, ran to each button is large enough to feed the chime[s],   add the third button crashes everything

If the length of wire is not large enough to cover the distance,  a voltage drop over the wire could leave you short of voltage,   which could easily explain why two work but the third cause the system of chimes to not work.

Corrosion, bad connections,  might be OK with 1/3 of the system but add on more and it becomes more of a problem.

The way I am understanding this,  you have three doors, with buttons, with a central chime,  so when a button is pushed,  you get a chime,  but have no idea which of the door switches is being depressed?

The most common is to have two switches at two doors,  the chime is for the front, the buzzer is for the back to identify which is being pushed.

So it is the same thing as the example of the indicator lights,  except we are trying to feed one chime with three buttons,       now the buttons should be switch legs,  like an ordinary switch,   but again, when all three are connected,  the size of the wire,  and the length are all interconnected,   

First you need to find out what the total power is for the main and only chime,   then you need to make sure the wire to each button is enough to handle the power needed to activate it,   and apparently even with two, it is a bare minimum situation.

It may be you only have enough transformer and chime for one button,  disconnecting all and trying one button should tell you if that is the case,    once you add on the second,  it should go back to barely operating,       if the components are not defective,  then it is a matter of too much load for the one chime transformer.

Again not knowing if all three worked before,   I have to assume they did not,     [because I see so many add ons, and then a new owner is trying to troubleshoot an inadequate system]

You can start this way,   identify as much data on wire and components as you can,   wire one switch to the main and only chime,   [in your case the transformer has to feed the all the switches,  and provide enough voltage that is not dropped over the length of the run to any door depending on the wire size.

Identify your two pairs,  and locations,   identify your one three wire  [which I would guess has three so it could be connected to another switch]

Start with one button and it's two wires to the main transformer/chime,   test.

Note results.

If adequate that one is most likely fine.

Next add on the second two wire to the main transformer/chime.

If both operate adequately,  you are done with two. but right now with two it barely works,  so  if switch one works fine,    then adding on switch two makes it work barely,   drop back to one switch,   recheck,      if fine,   remove one switch,  and connect number two switch,  if fine,    then the transformer/chime is too small, for two switches for some reason,  

The three wire probably has a white and red,  and maybe a black,  but one is most likely a common,      hopefully there is a red and white to start with,   connect it to the two that already operate,   if that kills the operation of the other two,   you have too small of a cable or too long of length or too small of a transformer.

Each switch must have adequate size wire for the length of the run, to operate the chime,  but you state with just two connected the chime works but barely,      

So you start with one,  if it operates properly,  you are probably OK,   add on number two and it operates barely, now both number one and number two become suspects,   

Any kind of corrosion on any switch, can drop voltage,   it might not matter for one, but when two are added  this becomes a problem.

I have no way to know if you have one chime with three different settings so you can identify which door is being activated,   

There is no universal color-coding for doorbell wiring, so it depends on how the installer hooked it up.
You're going to have to experiment with different connection combinations, or get an electrical tester and an assistant to push doorbells.
I highly doubt that the red and whites go together on any one screw, ever.
Have you looked at your transformer to see how it is wired?
The transformer should have one single wire from each button coming to one screw, and one single wire going from the other screw on the transformer to the TR screw on the chimes. See what those colors are.
Each button will have two wires...one wire going to the transformer (both on the same transformer screw), and the other wire going to the chimes (front or rear).

All switches and components should be rated for the same low voltage,  ie   is it a 16 volt or 24 volt system?  All components must match,,,,,,

Doorbell Wiring and Installation

A typical residential doorbell system includes a transformer (to convert 120VAC to 24VAC or lower), a bell/buzzer, and button for ringing the bell.  Residential door bell wiring uses low voltage except the line side of the transformer. The line side of the transformer must be terminated in an approved electrical box, similar to a light switch or wall outlet. The transformer is used to step the voltage down from 120V to 16, 18 or 24 volts. One or two buttons for front and back door can be used to activate your doorbell system. Below is a standard doorbell wiring diagram.  Since transformers come in a variety of voltages, be sure your transformer provides the correct voltage for your particular doorbell system.  They often come together as a kit, but sometimes you buy them separately.

Doorbell Wiring Diagrams


If your bell/buzzer only seems to support a single button, as shown below, it is still possible to wire two or more buttons to the system.  You merely connect both buttons to the same terminal.  You can connect two, three, four, or more buttons in the fashion if you really wanted to.


You can determine which side of the transformer is the line side, or 120V side, because it will usually have a black and white wires to connect to with wire nuts.  The low-voltage side will usually have a couple of screw terminals to connect your 18 gauge bell wire to.  See diagram below:

Doorbell "Bell" Wire

Doorbells are typically wired with 18 gauge wire, also referred to as "bell" wire.  Terminals on the buzzer/bell are commonly labeled "F", "R", and "C".  "C" stands for common and should be tied to one of screw terminals coming out of the transformer.  "F" stands from front and is used for the front door bell.  "R" stands for rear and is used for a rear door bell.  Many doorbell systems use a different buzzer or bell tone for front and rear so you can tell which button is being pushed.
Troubleshooting Doorbell Wiring

The following tips can be used to troubleshoot a doorbell wiring problem.  This is more common on doorbells of older homes that have suddenly stopped working but occasionally you'll find your new doorbell wiring is not working properly as well.

   Use a low-voltage circuit tester for testing the wiring arrangements for doorbells, buzzers or chimes. This type of tester is readily available at most hardware stores and home centers for a very reasonable cost.
   When problems arise, the doorbell button is usually the culprit. Always check the button first if a doorbell or chime fails to function. Metal fatigue in the spring or corrosion from the weather may cause the contact point to fail to function.
   After checking the bell button, inspect all visible sections of the wiring for breakage or mechanical damage.
   Use a low-voltage tester on each section of the wiring. You will probably locate a break in the wiring rather than a short.
   The bell will continuously ring–even when the button is not pushed–if you have a short somewhere in the wire.
   If the transformer has an overload protection device, a shortage may cause it to cut off the secondary current. So, the transformer should also be checked when problems occur.
   To check the transformer, disconnect one wire from the transformer's secondary screw. Touch the low-voltage terminal and the disconnected wire with the low-voltage tester.
   The bulb will light if there is a short in the wire. Be sure that the bulb you use in the low-voltage tester matches the voltage in the transformer. If you are using a lower-voltage bulb, it will burn out during testing. If you are using a bulb with a high-voltage rating, the light will simply be dim.
   Use a low-voltage tester to test the doorbell button. Connect the button from one transformer terminal through the bulb tester and back to the other terminal. If the button is working, the bulb will light when the button is pushed.
   If the trouble seems to be in the bell, buzzer or chime, the problem is usually in the connections at the contact point. Remove each connection wire, file it with sandpaper and replace each wire.
   More expensive chimes have solenoids that may be very difficult to replace. In some cases, these solenoids burn out and the chimes will fail to function. You may need to return the chime to the manufacturer for repair.
   When first installing a wireless unit, if the unit fails to operate, try plugging in the sound unit closer to the location of the pushbutton. You may just be out of the range of the small transmitter in the pushbutton.
   With the wireless units a weak battery in the pushbutton may cause the unit not to work. Check the battery with a low-voltage tester set to DC volts. If the battery is weak, replace it.

All doorbell systems (with the exception of wireless models) utilize a step-down transformer that reduces the home’s normal 120-volt circuit to a much lower voltage required by the doorbell system. The voltage needed can be anywhere from 8-volts to 24-volts, so it is very important that the correct transformer be purchased if you’re not purchasing a doorbell kit in which one is supplied.
Tools and Materials

   Insulated screwdrivers
   Power drill and bits
   Fish tape
   Voltage tester
   Wire strippers
   Torpedo level
   Needle-nose pliers
   Caulking gun
   Silicone caulk
   Ladder (if necessary)
   Wire connectors
   Doorbell buttons
   Doorbell chime
   Low-voltage bell wire (two-wire for running from switches to transformer)
   Low-voltage bell wire (three-wire for running from the transformer to the chime)
   Plastic anchors, toggle bolts or masonry anchors

How to Install a Doorbell or Chime
Step 1: Turn Power OFF
In every job in which you work with electricity, start by turning off the circuit breaker that delivers power to the circuit. Use the voltage tester to make sure the voltage is off.
Step 2: Run the Bell Wire
You should have two different types of bell wire for this installation, one that has two wires and one that has three wires. Run the two-wire bell wire from the transformer to the point where the doorbell button(s) will be installed. This will require you to use a power drill and fish tape to navigate the wires through the walls, across the ceiling, etc. Mark the wires with tape at the transformer so you know which one goes to which doorbell.
Next, run the three-wire bell wire from the transformer to the place where you are installing the chime.
Step 3: Mount the Chime
Position the chime on the wall where you want to install it. Place a torpedo level along the top to ensure it is level and use a pencil to mark its mounting holes.
If the wall is drywall, plastic anchors or toggle bolts will be suitable for mounting the chime, but if the wall is constructed of masonry material, screws with expansion sleeves or masonry anchors will be required.
Secure the chime using the anchors while keeping the bell wire accessible.
Step 4: Connect the Wires at the Chime
If you are installing a two-button doorbell system, the chime should also be supportive of two buttons. It should have three terminals, labeled F, T and B.

   F = Front door button
   T = Transformer
   B = Back door button

At the chime, the bell wire is three-wire, so remove about four inches of outer sheathing and you will see a black wire, a red wire and a white wire. Strip about ¾-inch of insulation from the ends of each wire using the wire strippers. Loosen the three terminals and secure the red wire under the terminal marked F; secure the black wire under the terminal marked T and secure the white wire to the terminal marked B.
Once the terminal connections are tightened down, install the chime cover.
Step 5: Wiring the Doorbells
Each doorbell should have a two-wire feed already in place. Remove about two inches of outer sheathing and you should see one red wire and one white wire.
At the front doorbell, strip ¾-inch of insulation from the end of each wire and connect the red wire to the bottom screw on the doorbell and the white wire to the top screw.
At the back doorbell, strip ¾-inch of insulation from the end of each wire and connect the white wire to the bottom screw on the doorbell and the red wire to the top screw.
Apply a bead of silicone caulk in the holes from which the wires extend and secure the doorbells to the jams using the included screws.
Step 6: Wiring the Transformer
At the transformer, you should have one three-wire cable and two two-wire cables (labeled per doorbell). Remove about four inches of outer sheathing from all three cables and strip the ends of all of the individual wires. Make your wire connections according to the following instructions:

   Connect black wire from the chime to one of the terminals on the transformer.
   Connect the red wire from the chime to the red wire from the front doorbell button.
   Connect the white wire from the chime to the white wire from the back doorbell button.
   Take the white wire from the front doorbell button and the red wire from the back doorbell button and twist them together and connect them to the other terminal on the transformer.

Make sure all wire connections are capped with a properly sized wire connector with no copper wire exposed.
Turn the circuit breaker back on and test your new doorbell chime system.

Let me know how it goes,  I can be reached at my shop   email is repair@mearservice.com  our repair phone line is 816-650-4030  MEAR Services Inc  Kansas City Missouri,   Buckner Missouri,  for industrial repair contact EMR Repair Inc,  service@emrrepair.com  repair phone number is 816-587-3930

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QUESTION: We have just moved into this house.  I will try disconnecting one of the bells to see if the other remaining operating one makes the chimee sound better, then I will know if the transformer is large enough.  I will start there.  Thank you

Logical diagnosis and easy to start with,   the odd thing is three buttons on one chime,   so someone comes to one of three doors and pushes the button,  how do you know which door it is?

Normally two buttons on one chime/buzzer,   the chime is on the front door,  the buzzer sounds when the back or less used door is pushed,      

How they wired these switches is anyone's guess,  but just from the fact it is not loud with two connected you do need to narrow it down to get one button to make the chime sound as you would think,  then add, one at a time,  testing between  the other two,     if adding one more lowers the chime,  then probably the wiring or switch is bad somewhere,  

I say that because   say the chime works fine with one button,        now disconnect that button and add the other,    if it works the same and good,     the problem is some interconnection of the buttons,  

Basically you would have one chime    one button it rings out fine,      now you parallel another button on top,   the first is open,  out of the picture,  push the second it should ring out fine too,   unless when the two buttons were installed,  when one is pushed instead of just ringing the chime it is wired into the second switch, dropping voltage, opening up, whatever,   but I like the one at a time plan
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Will Babbitt


Electrical issues of all types, wiring, control, appliances, components, specialty in Electric MOTOR or APPARATUS trouble shooting, electric motors, electrical problems, single phase, three phase, DC, capacitors, elevator MG-Sets, modifications, reverse engineering, VFD Drives, single to three phase convertors. Repair of most any electrical/mechanical/electronic apparatus, OEM, AC, DC, Industrial Applications, Three phase, single phase failure mode, determining the root cause of the equipment failure BEFORE failure repeats, Antique appliances, electric motors, fans, ceiling fans, base mount fans, poor equipment performance, Modifications, habitual failures, vibration, redesign, obsolete issues, collectible items restored, rewinding. Owner of EMR Repair Inc www.emrrepair.com More information on electric motors, under Engineering/Motors Ask about any electrical or mechanical problems in the home, office, or even at your work. B2B or business to business CONSULTING I can do but it would be a much more complex issue, that would require a significant amount of time. repair@mearservice.com from there we can discuss and begin work on about anything. Industrial electric motors, controls, troubleshooting, vibration, alignment, any type of industrial or commercial electric/electrcical equipment For the home owner, renter, apartment if you have odd things going on, describe to me, photos are normally very helpful, appliances, heating and air conditioning issues, light switches, installation, DIY PROJECTS FOR THOSE NOT EDUCATED IN ELECTRICAL, we can do some things, but for safety and sanity reasons, I may refer you to a local electrician, and help you find one, help you with pricing and even speak directly with anyone you hire if you have issues,


Over thirty years with a major repair and sales company, VP of Operations, and former owner of my own specialty repair shops, MEAR Services local to Kansas City Missouri EMR Repair Inc., located in Kansas City Missouri, 2014 sold both businesses to JCI Industries, Lee's Summit Missouri wbabbitt@jciind.com Evaluation and repair of electrical/mechanical apparatus. Electrical and mechanical repairs, trouble shooting including, vibration and balance issues. About.com provides this service, and the huge costs to provide help on about any subject. They provide the servers, the people to vet the experts, costs that would be the same as operating a good sized business, They should be appreciated for what they do, the huge costs and the great help they provide for free, Electric motor questions, can be answered here but there is a dedicated category that has other experts to help and add to a solution. Other common questions, are noises in the walls, breakers tripping, devices not starting or shutting down for no apparent reason, smoke alarms buzzing, thermostat change outs, or sizing wire or needing information for a new project, but anything can be resolved, anything, with enough effort and patience, DIY, with electrical is possible, but in most cases the use of a simple ohm meter or volt meter is needed, they can be purchased at any hardware store for a few bucks. If you have smoke, or smell smoke, don't be writing me, call 911 the Fire Department has no problem looking for smoke smells, better then spraying water on a blazing fire. DO NOT GET CAUGHT INVESTIGATING AND TRAPPED IN A BASEMENT LOOKING FOR A BLOWER FAILING< As to the tip jar, it is up to you, it is appreciated, every expert spends out of pocket that I know, we spend on IP time, computer wear, printing documents, books, and of course our time, but if we prevent a $400 service call, we did well,

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