Why Does My Doorbell Button Have Three Wires?
August 2, 2021 11:52 AM Subscribe
Like everything else in my house, my doorbell button is an anomaly with three wires. I am trying to replace the buttons, but no one believes me that there are three wires instead of two. Since it’s low voltage at the buttons, can I just short out combinations of two wires until the bell rings? What’s the third wire for? An illuminated button?
Note that I am talking about the doorbell buttons. Not the transformer. Not the bell mechanism.
There are three wires. I’ve looked at close to 50 doorbell diagrams now, but none of them show three wires at the buttons.
The house has a button at the front door and the back door, but they were broken off and not working ever since we’ve lived there.
I know the wires and bell mechanism work because when took off the broken button, the wires touched and the bell rang.
But now I have three wires instead of two. Can I just touch them in combinations of two until the bell dings? What’s the third one for? To light up a button?
I don’t plan on turning off the power because it’s low voltage at the buttons and I need to know which two buttons to use with the power in order to short them anyway. But that third wire…
The house is 1939, but the doorbell transformer location is unusual, so assume the doorbell itself is from c1988 during the house remodel.
Note that I am talking about the doorbell buttons. Not the transformer. Not the bell mechanism.
There are three wires. I’ve looked at close to 50 doorbell diagrams now, but none of them show three wires at the buttons.
The house has a button at the front door and the back door, but they were broken off and not working ever since we’ve lived there.
I know the wires and bell mechanism work because when took off the broken button, the wires touched and the bell rang.
But now I have three wires instead of two. Can I just touch them in combinations of two until the bell dings? What’s the third one for? To light up a button?
I don’t plan on turning off the power because it’s low voltage at the buttons and I need to know which two buttons to use with the power in order to short them anyway. But that third wire…
The house is 1939, but the doorbell transformer location is unusual, so assume the doorbell itself is from c1988 during the house remodel.
To light up a button?
That'd be my guess. Do you not have a voltmeter? You can check continuity to the bell and check voltage that way.
posted by Brockles at 12:07 PM on August 2, 2021 [4 favorites]
That'd be my guess. Do you not have a voltmeter? You can check continuity to the bell and check voltage that way.
posted by Brockles at 12:07 PM on August 2, 2021 [4 favorites]
It could also be that the installer used a cable with 3 conductors in it and only wired up two of them. If it's low voltage, I'd assume that momentarily shorting each pair until you hear the chime should be fine, but you might want to check with a voltmeter first.
posted by Aleyn at 12:23 PM on August 2, 2021 [4 favorites]
posted by Aleyn at 12:23 PM on August 2, 2021 [4 favorites]
I'd search for the transformer and examine the wiring to it and the actual chimes for clues.
posted by achrise at 12:25 PM on August 2, 2021 [4 favorites]
posted by achrise at 12:25 PM on August 2, 2021 [4 favorites]
Light up doorbells work with two wires. I don't think that's the answer. And this won't be line voltage, so I don't think you're going to be seeing white, black, and green (well, if you do, it may not have the same meaning). I agree that the best course of action is to trace it either with a voltmeter or by looking at the chime end, or both.
If there were two buttons controlling one chime, I wonder if this is like a 3-way light switch circuit (I have never seen a two-location door bell, so I have no idea if that's how it would be done; I'm just speculating).
posted by primethyme at 12:29 PM on August 2, 2021
If there were two buttons controlling one chime, I wonder if this is like a 3-way light switch circuit (I have never seen a two-location door bell, so I have no idea if that's how it would be done; I'm just speculating).
posted by primethyme at 12:29 PM on August 2, 2021
This is not how two-location doorbells work, mine has separate chimes so you know which doorbell your caller is pressing. Agreed that the installer probably just used the cable with an extra wire because that’s what they had, and that a voltmeter is an ideal solution, but pairing off wires should work fine.
posted by momus_window at 12:43 PM on August 2, 2021
posted by momus_window at 12:43 PM on August 2, 2021
To expand on Aleyn's comment- using three conductor wire to go to the doorbell chime itself is common (usually the chimes have 3 separate terminals -one for the front chime, one for the back chime and a shared common terminal) So, the installer used what was on hand. You're probably pretty safe just finding whichever combo of wires makes the chimes ring. Touch the wires together very briefly, in the off chance someone ran both the hot and neutral wires from the transformer out to the button. In my experience, doorbell transformers will be fine with a momentary short circuit. If it rings, you're golden.
posted by Larry David Syndrome at 12:49 PM on August 2, 2021
posted by Larry David Syndrome at 12:49 PM on August 2, 2021
Maybe add some pictures?
posted by theora55 at 1:13 PM on August 2, 2021 [1 favorite]
posted by theora55 at 1:13 PM on August 2, 2021 [1 favorite]
See if you can find the end of the runs.
There are three basic ways that the wires could be run:
1) From the doors to the transformer, where you would find two door runs and a bell run
2) From the doors to the doorbell bell itself, in addition to a run from the transformer
3) At some intermediate point, which, if it was a remodel, is probably not actually buried inside a wall, but could be (for ex.) behind the doorbell, or done behind a wall switch blank (especially in closets, etc).
Simply looking at how it is wired together is the thing that will give you the correct answer, but knowing the specifics in a remodel can be a bit dicey.
In practice, a low voltage doorbell transformer does not put out much juice and can be shorted out safely. However, it is very unlikely that there would be any reason to run voltage out to a doorbell on a conventional system, so the previous suggestions of simply shorting wires until it rings are totally the thing low voltage professionals do all the time. There are only three permutations. If one works and two don't ring the bell, cap that unused wire and be done with it.
posted by jgreco at 1:37 PM on August 2, 2021 [1 favorite]
There are three basic ways that the wires could be run:
1) From the doors to the transformer, where you would find two door runs and a bell run
2) From the doors to the doorbell bell itself, in addition to a run from the transformer
3) At some intermediate point, which, if it was a remodel, is probably not actually buried inside a wall, but could be (for ex.) behind the doorbell, or done behind a wall switch blank (especially in closets, etc).
Simply looking at how it is wired together is the thing that will give you the correct answer, but knowing the specifics in a remodel can be a bit dicey.
In practice, a low voltage doorbell transformer does not put out much juice and can be shorted out safely. However, it is very unlikely that there would be any reason to run voltage out to a doorbell on a conventional system, so the previous suggestions of simply shorting wires until it rings are totally the thing low voltage professionals do all the time. There are only three permutations. If one works and two don't ring the bell, cap that unused wire and be done with it.
posted by jgreco at 1:37 PM on August 2, 2021 [1 favorite]
I think the question is if the doorbell buttons you removed actually have three terminals that the wires were screwed into (in which case, confusion is continued - maybe post pics of those and the wires). If not, and these are three wires to the doorbell but where only two were connected, it's really most likely that the builder just had three-wire cable with them, didn't want to get two-wire cable, and just installed three-wire and connected two.
posted by eschatfische at 1:56 PM on August 2, 2021 [2 favorites]
posted by eschatfische at 1:56 PM on August 2, 2021 [2 favorites]
The installer just had 3 conductor on his truck so used that instead of two (this is pretty common, the price between the two per foot is minimal and by only having three conductor (needed for furnaces) you saved rack space in the truck). Modern systems require 4 or 5 conductors and it's still common to just run that for everything including doorbells.
Just short pairs together till the chime rings. You can't hurt a doorbell transformer by shorting it out because its internal resistance is too high.
posted by Mitheral at 2:25 PM on August 2, 2021 [2 favorites]
Just short pairs together till the chime rings. You can't hurt a doorbell transformer by shorting it out because its internal resistance is too high.
posted by Mitheral at 2:25 PM on August 2, 2021 [2 favorites]
If the installer just used the 3 wire cable for convenience then that extra 3rd wire wouldn't be stripped down to bare metal in preparation for being attached to the button. Only two of the wires would be stripped.
If the house is originally 1939, even with new doorbell equipment using old wires then the 3rd wire might be stripped for the original system. It's probably not that easy to do light and button over just two wires using 30's era electronics.
I'd vote for one wire being ground, one being hot for the light, and one going to the bell. Simple 30's brute force. Once you've found the two that make the bell ring, tape up or do something to the 3rd wire, it might be bad to leave it dangling around.
posted by zengargoyle at 3:06 PM on August 2, 2021 [2 favorites]
If the house is originally 1939, even with new doorbell equipment using old wires then the 3rd wire might be stripped for the original system. It's probably not that easy to do light and button over just two wires using 30's era electronics.
I'd vote for one wire being ground, one being hot for the light, and one going to the bell. Simple 30's brute force. Once you've found the two that make the bell ring, tape up or do something to the 3rd wire, it might be bad to leave it dangling around.
posted by zengargoyle at 3:06 PM on August 2, 2021 [2 favorites]
If you are worried about touching bare wires together, you can put something with a little electrical resistance between them, maybe a flashlight bulb.
posted by SemiSalt at 3:39 PM on August 2, 2021
posted by SemiSalt at 3:39 PM on August 2, 2021
It's probably not that easy to do light and button over just two wires using 30's era electronics.
It's actually really easy because electronics aren't required just clever application of electrical theory. You choose a bulb that doesn't allow enough current flow to activate the chime. When you press the button it shorts the bulb allowing a lot of current to flow which activates the chime.
You can't really read too much into what wires are stripped on equipment this old because you don't know the history. I mean if only two wires were stripped then that would be my first guess but I wouldn't be surprised at all to find out those weren't the right combination.
posted by Mitheral at 6:09 PM on August 2, 2021 [2 favorites]
It's actually really easy because electronics aren't required just clever application of electrical theory. You choose a bulb that doesn't allow enough current flow to activate the chime. When you press the button it shorts the bulb allowing a lot of current to flow which activates the chime.
You can't really read too much into what wires are stripped on equipment this old because you don't know the history. I mean if only two wires were stripped then that would be my first guess but I wouldn't be surprised at all to find out those weren't the right combination.
posted by Mitheral at 6:09 PM on August 2, 2021 [2 favorites]
Then if your lightbulb burns out your doorbell doesn't work.
posted by zengargoyle at 6:51 PM on August 2, 2021
posted by zengargoyle at 6:51 PM on August 2, 2021
Oh, if we're still guessing. One wire is ground, one is -X volts, the other is +X volts and they go to a bi-directional solenoid with springs hung between two chimes so that connecting (and releasing) the - side goes DONG-DING and connecting the + side makes it go the other way and DING-DONG.
Yeah, take a look at the transformer and chimes and stuff and get a cheap multimeter and it's probably not hard to figure out. Otherwise, experiment.
posted by zengargoyle at 7:01 PM on August 2, 2021
Yeah, take a look at the transformer and chimes and stuff and get a cheap multimeter and it's probably not hard to figure out. Otherwise, experiment.
posted by zengargoyle at 7:01 PM on August 2, 2021
Then if your lightbulb burns out your doorbell doesn't work.
It just acts as a non-illuminated switch. In the diagram I linked a burned out bulb acts the same as if there was no bulb in the circuit at all.
posted by Mitheral at 7:49 PM on August 2, 2021
It just acts as a non-illuminated switch. In the diagram I linked a burned out bulb acts the same as if there was no bulb in the circuit at all.
posted by Mitheral at 7:49 PM on August 2, 2021
Response by poster: It gets more confusing, but I got it sorted.
It was actually four-conductor wire, with the yellow broken off inside the sleeve. And all four wires were live, and they sparked like a sun-of-a-gun, too.
I found the rear doorbell connection with remnants of a doorbell, and the wires were connected in pairs.
Black/yellow together and red/green together, even though the bell still worked with only touching two wires instead of four, so it’s like it was doubled up for no reason.
Same colors front and back, but only one set of four at the bell: red to rear, green to front, black to transformer, yellow cut off.
Yet the front door dings the bell and the back door clicks the plastic instead of hitting the bell.
I’m not sure how it’s wired between the transformer and the bell, and I don’t know why it’s redundant at each door, but it works.
posted by TinWhistle at 12:18 PM on August 5, 2021
It was actually four-conductor wire, with the yellow broken off inside the sleeve. And all four wires were live, and they sparked like a sun-of-a-gun, too.
I found the rear doorbell connection with remnants of a doorbell, and the wires were connected in pairs.
Black/yellow together and red/green together, even though the bell still worked with only touching two wires instead of four, so it’s like it was doubled up for no reason.
Same colors front and back, but only one set of four at the bell: red to rear, green to front, black to transformer, yellow cut off.
Yet the front door dings the bell and the back door clicks the plastic instead of hitting the bell.
I’m not sure how it’s wired between the transformer and the bell, and I don’t know why it’s redundant at each door, but it works.
posted by TinWhistle at 12:18 PM on August 5, 2021
Maybe there are two chimes—so you can distinguish which door—and they installed it so both rang both of them because genius installer?
posted by Gilgamesh's Chauffeur at 4:22 PM on August 5, 2021
posted by Gilgamesh's Chauffeur at 4:22 PM on August 5, 2021
This thread is closed to new comments.
posted by rozcakj at 12:06 PM on August 2, 2021