How to Diagnose and Repair Three-Way Switch Problems | All About Lights | Ask This Old House

uh we have a switch here that works just fine and another switch over here it also works just fine i don't know okay if you turn the light off then this switch does not work oh and same thing when that's off this switch oh boy it does not work wow yeah so we're kind of going back and forth my husband and i get confused about which switch actually works all right well it's not uncommon to have two switches controlling one light and i think the problem is not uncommon either i see it a lot so let me grab some stuff out of my truck i think it'll be easier for me to explain actually what's going on great thanks all right jenny take a look over here you've actually got a couple of different types of switches here all right so this middle switch here which controls this hallway light when you shut it off it says off right on top of the switch okay now when you turn it on you can see it says on down below right now this other switch which controls the dining room light has no writing on it at all which is a good thing because that switch or this switch i'm made to operate that light in either of the two positions okay let me show you what i mean so i have a switch here so this is the single pole switch with the on off written on it it only controls the light from one location i've brought a cutaway here you can see that when the light switch is down in the off position the two contacts are actually not touching on the inside so normally the power comes into either one of these two screws and then it goes out to the lights from the other screw when it's in the off position this is broken right here they don't touch each other when you put it in the on position you can see the contact is now made these are connected turning on the light now what you have in your dining room is a three-way switching system okay so we have two switches controlling one light and this is a three-way switch there's a black screw right here and then two same color brass screws when the switch is in one position you can see that the connection is made here however on the other side the connection is broken when you flip the switch into that position it makes this connection on this side and breaks the connection on that side so what that means is that the black screw is either sending power to this screw terminal or when the switch is in the other position to that screw terminal the black terminal is called the common and it either wires to the power source or the light fixture the brass terminals are called travelers and there are two travel wires that connect the traveler's screws on the two switches when the light is on power is flowing from the source across a travel wire to the light fixture however when you change the position of one switch that path is now broken and the light turns off the power has two possible paths and either switch should be able to turn the light on or off at any time so what i think happened is two wires were probably just mixed up the common wire and the travel and wire all right you could show me where the electrical panel is we'll shut this power off and take a look it's right over here all right good all right i've shut the power off to this switch taken the plate off and pulled out the switch the power originates from this location and everything looks great okay however over here i found a problem we have two wires that go down into this box they both have a white and a bare ground wire now this one has a black wire that goes up to the light fixture okay that's supposed to tie on to the black common screw okay this cable has a red and a black and they're supposed to tie into the brass traveler screws doesn't matter which one goes away now if you look inside the box here you can see this wire here on the right is the wire that's supposed to go up to the light fixture and these two wires on the left here are the wires that are supposed to go to the travelers so take a look what they did here the red travel wire is actually tied into the black carbon screw oh okay and the black common wire is tied into one of the brass travel screws okay how do you think that happened well my guess is that this switch was probably replaced from the original switch homeowner possibly because you can tell that screw right there they wrap the wire around counterclockwise that's not correct oh it's supposed to go around the screw clockwise so when you tighten it it tightens the wire around it okay but it's an easy fix we'll just swap these two wires okay okay the power is back on go ahead hit the switch okay it's on now the other switch all right we got it off all right now the big question is will this switch turn the light back on ah it did excellent you

Channel: This Old House

Views: 420,274

Keywords: this old house, how-to, home improvement, Episode, TV Show, DIY, electrician Scott Caron, Ask This Old House, light switches, pliers, screwdriver, three-way switch

Id: LozeRVU7YKU

Length: 5min 54sec (354 seconds)

Published: Mon Nov 21 2016