I just purchased on old loft. I opened a four panel box (I want to swap out some of the switches for dimmers) and discovered the following:

B/W/R B/W/R B/W/R B/W

B/W/R

So four sets of wires coming in from the top of the box (three sets of Black/White/Red and one set of Black/White) and one set of wires coming in from the bottom of the box (Black/White/Red). Assume I number each wire as follows:

B1/W1/R1 B2/W2/R2 B3/W3/R3 B4/W4

B5/W5/R5

B1, B2, B3, R3 and B5 are the hot wires.

All of the wires are hooked up to the same fuse (the one that controls the ceiling lights), except for R3. R3 is hooked up to the fuse that controls a plug near the box, and is tied together with B4 and B5.

Why are R3, B4 and B5 all tied together? What is the purpose of this?

Thanks.

I;m hoping you didn't disconnect anything before making a diagram. If you are replacing a switch with a dimmer, just connect the two wires from the dimmer to the same two wires the switch was wired to.

To answer your question, we need some more information:

Call your switches S1, S2, S3, and S4. Each switch has two terminals, label them S1A, S1B, S2A, S2B, etc. (If a switch has three terminals, label them A, B, and C. In this case, one terminal screw is a darker color than the other two, make sure you include this information.

Now, tell us exactly which wires are connected together and to what switch terminal they go to. Tell us which set of wires go to the receptacle.

Also list any wires that are connected together but do not go to a switch.

With only the information you provided it appears that Cable 3 is the homerun for a multiwire branch circuit. Basically, two circuits on separate phases that share a neutral. So think of it a two circuits B3 and R3.

Cables 1 and 2 feed lighting and either each is controlled by multiple switches or R1 and/or R2 are unused. Cables 1 and 2 are on the B3 circuit.

Cable 5 probably supplied power to a duplex receptacle that was split with one switched and one not. It was probably changed to fully unswitched at some point leaving an unused wire. Cable 4 simply provides power to other outlets on the R3 circuit and almost certainly was never connected to a switch.

Of course this is all just one part experience and four parts assumption. I can think of several other scenarios if you want but this one is what I would be thinking while tracking it all down.

Thanks. Maybe there is a method to the madness, but the wiring looks quite arbitrary. I don't propose to know anything about wiring, but I would have thought that you would have a black (hot) and red wire running to each switch. For example, S1 would be connected to B1 and R1, S2 would be connected to B2 and R2, etc. Instead, they have wires and switches connected all over the place (including to one another). Why would this be the case? For instance, S1 is connected to R2 and R5, but the connection to R5 is spliced so that it also connects to S2 (which, in turn, is connected to B1 and B3). Can I simplify this?

Put another way:

R1 is connected to S1
B1 is connected to S2

R2 is connected to S4
B2 is connected to S3

B3 is connected to S3
R3 is connected to the bundle referred to above

B4 is connected to the bundle

R5 is connected to both S1 and S2
B5 is connected to the bundle

S2, S3 and S4 are also all connected to one another

Do what ohb0b suggested:


Call your switches S1, S2, S3, and S4. Each switch has two terminals, label them S1A, S1B, S2A, S2B, etc. (If a switch has three terminals, label them A, B, and C. In this case, one terminal screw is a darker color than the other two, make sure you include this information.

There are three S2's and three S3's in your list. Is that S2a, S2b and S2c?