So I'm swapping out this old switch for a new decorative paddle one and found that it has four wires attached. Two black attached to the bottom right, one black to top right, and one red on the top left? Is this safe? What would the purpose behind this be? And is it possible to buy this switches still? Thanks![Switch

  • 3
    That's a 3-way switch. There must be another that controls the same lighting circuit. – isherwood Jul 12 '18 at 15:11
  • And yes any switch you buy in single pole will also be available as a 3-way switch. It’s important right now to know which wire connectors to the screw color that’s different from the other two screws. – Tyson Jul 12 '18 at 15:14
  • Disregard position. You just listed the position of the 3 groups of wires. That information is useless. Two of the connections (almost certainly the singles) will be traveler wires and will be on brass screws. That is the information you need to capture. I recommend getting a 5-pack of colored tape and marking each traveler with yellow tape. They are interchangeable so you don't need to tell them from each other. In fact in conduit wiring I just use 2 yellow wires. – Harper - Reinstate Monica Jul 12 '18 at 18:22

You need a 3-way version of the switch you have

Take the new switch you got back to where you got it and ask them for the 3-way version of it, as your existing switch is quite clearly a 3-way switch. Once you have a 3-way switch in your hands, there will be 4 terminal screws on it: 1 green ground screw, 2 screws with the same color (often brass), and 1 differently colored (usually black) screw.

The red wire in your photo above went to the differently colored (black) screw on the old switch, so it goes to the differently colored non-ground screw on the new switch, while the top black wire in your photo goes to one of the same-colored non-ground screws on the new switch. The two remaining black wires get nutted to each other and to a black pigtail going off to the remaining same-colored non-ground screw on the new switch, while any ground in the box should be connected (or pigtailed, if there is not a ground pigtail coming out already) to the green ground screw on the new switch.


The screw on lower right is probably being used to connect those two (black) wires to each other. The fully correct way to do this is to secure the two wires and a third short wire (called a "pigtail") with a wire nut and secure the other end of the pigtail under the screw.

If the switch you are using has wire leads, you put the correct lead in a wire nut with those two black wires. That screw on the bottom is the common. In one set-up with two 3-way switches the line hot is connected to the common of one switch and the load (the light) is attached to the common on the other -way switch.

If the pair of switches is controlling more than one light fixture, then multiple cables will be needed. The cables for multiple lights could all be connected in one box with one of the switches or a single cable might go from one switch to one light, another from the 1st light to a 2nd light, etc. Or some combination of these two.

If one of those two black wires is the line hot (always hot), then the other black wire is carrying the line hot to somewhere else. (If neither of these two wires is the line hot, and there are multiple lights controlled by this switch, then these might be wires to the two lights.

The operation of the normal 3-way switch is to switch the common to one or the other of the other two screws. That is why the normal 3-way switch does not have "on" or "off" on the switch; it has two different "on" states and no "off" state.

  • "The fully correct way...with a wirenut.." Not in the UK it isn't. Wirenuts are not allowed as too dangerous. Wago or choc-block please (or junction box). UK connectors are usually sized for two wires to go into them (and then you screw down on the pair) - so no need for a pigtail at all. German fittings typically seem to have a pair of Wago-like connections, so again, no need for a pigtail. – Martin Bonner supports Monica Jul 12 '18 at 19:34
  • I am pretty much of a safety obsessive. I know wire nuts are not allowed in the UK and I accept that the connection methods in the UK are very likely safer than here in the wild west. Thirty-eight years ago I pigtailed my aluminium wired branch circuits with superior quality wire nuts into which I had squirted anti-oxidant grease. I am now redoing these with AlumiConn screw connection blocks. I think the WAGO lever connectors would work (with WAGO joint compound, but officially they are not approved for Al. I had one wire nut failure (not my work), one nut holding 4 or 5 #12 Al. – Jim Stewart Jul 12 '18 at 19:46
  • Ah. By "Wago" I meant the push in/twist and pull to remove ones - not the lever ones. I'm coming to the view that the German system is safer still (it eschews ring mains). – Martin Bonner supports Monica Jul 12 '18 at 19:56
  • @MartinBonner -- the wiring device in the querent's photo is very clearly North American in origin :P – ThreePhaseEel Jul 12 '18 at 23:07
  • @ThreePhaseEel But a) this is an international site, and other readers who visit the question later may not be North American; b) North Americans might want to consider if wirenuts actually are safe (given that many parts of the world forbid them). – Martin Bonner supports Monica Jul 13 '18 at 5:39

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