House Wiring -Diagrams of Connections

Chart of the possible wire functions for two-wire and three-wire cable (14-2, 12-2, 14-3, 12-3). This chart will apply below to the diagrams (Fig.1-7) and all their Commentary, and to the Cable-and-Box Chart below that. New window of these comments.

The status or intended function of each insulated wire in any cable will be one of these:

Hot =live =being 120 volts in relation to ground =able to shock
Neutral =grounded white wire for carrying circuit current back to the source
Switched =hot only at times (when switch is "closed")
Traveler =a particular switched (hot at times) wire that is to be hot when its partner-traveler is not
Dead =neither hot nor grounded =floating =what a switched wire is when it is not hot. (No always-dead wire is shown in the chart because the chart is to show functions, not lack of function.)

The chart shows us that any two-wire cable in your home can be given one of four names, according to the combination of its black-wire and white-wire functions. All three possible combinations of the first three functions -- hot, neutral, switched -- have their cable-names. I suppose theoretically a cable could have one wire be hot or neutral and the other be a traveler, but this is never really done. Since the travelers are needed as a pair, they have their own cable: "x". Its nickname is not established. By the function of its wires, it could be called a traveler cable or a 3-way cable.

Likewise, we can designate five wire-uses possible within three-wire cables. We do not have to divide the 3-way switching cables -- "n" and "t" -- into separate categories, the way I have done. However, the most common 3-way/4-way wiring does have a neutral accompany the travelers, and since the neutral must be white, the travelers' colors are determined. In contrast, the wires of an n-cable have more color leeway because by definition no wire is a neutral in them.

Other notes: The use of red as a switched wire in f-cables is only conventional, not a matter of house wiring color Code... The two hot wires in a d-cable are supposed to be 240 volts apart from each other, which is set up by how their two breakers are arranged in the panel. These hots are still each 120 volts in relation to ground.

As you can see, in any cable the only reliable meaning that wire color will have is: reds and blacks will not be neutrals.

Realize too that, in spite of its intended function or tested characteristics, a wire's actual status can change. Any switched wire is an example of this already, being hot or dead at the whim of the switch. But in addition the failure, undoing, or misconnection of wires at one point along a circuit can make some other wires lose their intended character. A "neutral" could become hot. A hot could become switched or dead. Since these disconnections and misconnections are exactly what you may be involved in solving, until they are all solved, you will need to watch your wire-identity assumptions closely. 

Figure 1 (Switches) Commentary. New window.

All the diagrams of this tutorial are to illustrate most of what you might run into in a home -- or might need to reconstruct if you undid some wiring connections. FIG.1 may be the granddaddy of all house wiring diagrams of connections. The letters on the cables in it are my code for the main ways that 2-wire (flat, black-white) and 3-wire (round, black-white-red) cables and their wires may be functioning in any electrical box in a home. The Cable-and-Wire Functions Chart above explains the meaning of these code letters.

The big blue wirenut loaded with black wires distributes electrical "hotness" from the black of one of the p-cables ("p" is for "power"). This p-cable is bringing the circuit's hot and neutral to this 9-gang (!) switch box. Which p-cable is doing this doesn't matter for our purposes at the moment. That black wire's hotness gets extended to a lot of other black wires by virtue of their all being in contact in that big wirenut. Likewise "neutralness" is spread to several other white wires by that p-cable's white. That cable is coming from somewhere earlier in the circuit and so, ultimately from a circuit breaker in the electrical panel.

The two other p-cables are passing the circuit (constant hotness and neutralness) on to other places/boxes downstream -- further along. One might be going to another switch box and the other to an outlet or light box. Actually if you look carefully there is one other cable that takes hotness from the big wirenut without passing through any switch... Yes, cable-f.

3- Cable-f's red wire is getting switched by switch-3. Whatever it is that is getting switched -- a light or outlet -- is also getting a constantly hot black wire, for whatever reason. Maybe a light's box is just going to pass that hotness on to an outlet beyond it. The red is fed with the hot and neutral (=power) wires.

1 & 2- OK, that leaves "L" and "h" and "m," on the left side of this box. That's enough to deal with at the moment. Cable-"L" means it goes to switch a light or plugged-in lamp. Its black is being switched on or off by switch-1. Switch-2 is pretty simple too and was the basic way of switching house lighting through the 1960s. But since then, the switch-1 arrangement -- where the neutral wire goes with the switched hot up to the light -- has become more common. Then what is the white wire going out in cable-h from switch-2? It is a constant-hot coming to our box from the light or switched-outlet box. Why not just use the hot available out of our big box? Who knows? People wire in various ways. And why do I call this wire usage "h"? For the white wire of a 2-wire cable being hot. Some call this cable function a switch loop.

4 & 5- Cable-m, having the extra red wire, is able to go to switch two things, each having its own switch. M is for "multiple." An example would be a fan/light, whether it be a ceiling "paddle" fan with a light on its bottom, or a bathroom exhaust unit that includes a light. Can such things share a single neutral wire? Yes, and if you think about it, the various things on a given circuit are usually all sharing its one neutral that lands in the main panel.

As we seem to be going from left to right, the rest of the switches are different. They are not "single-pole" switches, inside which a single contact point makes or breaks the connection between the two wires. They are three 3-way switches and one 4-way switch. When they break connection from a second wire, they make connection to a third, generally. See 3-way switches. Of these next switches, only switch-7 seems to be using the circuit's hot. Are the others running from other circuits? Well, they could be, but let's say they are not. Since they are all working in conjunction with partner switches from the other side of the room or down the hall, those locations may have our circuit's hot available at them, and we only want it hooked up at one end of a pair of 3-ways switches.

7- So what about switch-7? It is being the "hot end" switch, and its partner (wherever that is) will be the "leg end" -- finally giving or withholding hotness from the light they control. The white wire of cable-7 is not a neutral; it is a sometimes hot "traveler" -- hot or not, according to the switch-handle's position. Like switch-2, 7's light must be getting the neutral it needs from elsewhere.

6- Backtrack to switch-6, perhaps the most common wiring look of 3-way switches. Its travelers are part of a 3-wire cable ("t" -- for threeway), which is more commonly the case for 3-way systems (in contrast to cable-x). But rather than being the hot-end of its 3-way system, switch-6 is the leg end, feeding the system's decision (hot or not hot) up to the light on nearby cable-L, along with the light's neutral, which has been brought over in cable-t from the hot-end switch (on the other side of the room).

8- If switch-2 and cable-h looked like they only had eyes for each other, so do switch-8 and cable-n. Each cable attaches only to its switch... Since cable-n's red and white are attached to same-color screws, they are travelers. Then is its black a constant hot (making this 3-way switch the hot end of the 3-way system)? It might be but I'm not saying that it is. It might be a hot or it might be the switched "leg" to the light, making this switch the system's leg end... I needed a category and code-letter for all the 3-way switch wiring methods that use 3-wire cable but do not carry a neutral in them. That's why I call switch-8's cable "n".

9- The best for last. On the far right is a 4-way switch -- switch-9. This one shows how the traveler pairs from two three-wire cables connect to the two pairs of traveler terminals on the switch. The reds would not have to be on the right side or even on the same side. The main thing is that each cable's travelers hook to a pair of same-color terminals. Are these white wires neutrals? In this case, yes, and that is why the cables are labeled "t", meaning the three-way cables that have a neutral and two traveler wires. To review how a 3-way switch system works see 3- and 4-way switches.

Figure 2 (Switches) Commentary (Compared to Fig.1 Above) New window.

In puzzle books they sometimes have two pictures for you to look for the small differences between them. I hope you like those. The switches and most of the cables in FIG.2 below are the same as in FIG.1 above that you just got intimately acquainted with. But most connections are different. Take a look at where the big blue wirenut was. Instead of nine wires there are only three there now. What has happened? For one thing (again starting from left to right) one cable-p is now designated as cable-d, which means it is a 3-wire cable bringing two circuits ("double") into our box, with their one shared neutral. If you follow the new added red circuit, you see that it only ends up involving switch-13 and cable-f. We will assume the rest of the switches and cables still run on the black circuit (whether or not their connections to the black circuit happen in our big box).

13- Cable-f and switch-13 are still doing what they always did -- back when it was switch-3 above. But the hot must have its own connection -- one of three new wirenuts -- to keep it separate from the black circuit's hots, which are 240 volts at odds with this red hot.

11- Even basic switch-1 is now connected differently as switch-11. Its lower terminal is not only getting a hot black from the wirenut as before, it is providing a new place for second-position cable-p's black to get connection to hotness -- rather than at the wirenut. Since putting two wires under one screw terminal makes an unreliable connection, let's assume the diagram means that one of those two blacks is actually attached by poking into a hole-terminal on the back side of the switch. Switch-11 also has two cable-L's that it turns on now. (The cable in that position had functioned as a p; now it is an L.) Their blacks are using a pigtail from one of the new wirenuts, to get their connection to switch-11. Instead of a pigtail, I suppose they could have both connected directly to the top switch terminal in the fashion shown at the lower terminal.

12- Switch-12 and cable-h are functioning as always, but their white wire is red part-way. This painting or taping is a current Code requirement, so that the white is not mistaken for a neutral. But to keep from assuming it is part of a 3-wire cable, a troubleshooter will want to doubt such reds, or even blacks, by looking closely at the color where the cable comes into the box. Just as you might see that someone had dyed their hair by looking at the roots.

14 & 15- Speaking of whites that are not neutral, look how cable-m no longer has a neutral. Now its white is doing something else. In fact, it is doing what switch-12's "reddish" white does, but for two switches. The white is a hot wire coming down from a light-fan or such, to power up the two switches. We still designate the cable as "m," even though its use is reminiscent of 2-wire h-cable.

16- Take a look at switch-16. Something different is going on... As #6 in Fig.1, it was acting as the leg-end of a 3-way system. Now it is the hot-end. Cable-t still carries red and black as travelers and the white as neutral, but this time the neutral is coming from our box, and the leg cable (not the L shown here!) for this 3-way system is going to the light from another switch box than ours. Cable-L above switch-16 no longer belongs to 16...

17- ...It is being lit up by switch-17, which is no longer the hot-end of its 3-way system; it is the leg end. Our box could be where that cable-L would get its neutral, via the wirenut that is also feeding neutral to cable-t. But L's white wire is not in that nut! Did I goof up? I've been known to, but in this case this "White to Nowhere" is just x-tra. As author of this scenario, I know that the light which cable-L is going to, will have a neutral from another source. If all whites that were not hot, switched, or needed as neutrals were always hooked to neutrals, we would get some situations of "parallel conductor" paths for current to run on. Though not generally dangerous, it makes for confusion -- maybe more confusion than seeing a white wire cut off by itself here and there! Then why is that tempting wirenut even there near cable-L? Couldn't cable-t's neutral have gone directly to the big wirenut in the lower left of our box? Yes, but let's say there wasn't enough wire to reach. It is OK to extend wires in a box or panel this way.

18- Switch-18 now relates to a 2-wire cable in addition to its original 3-wire cable. Still true to n-ness, cable-n's white is Not Neutral. So what is going on? The two-wire cable-h is bringing a hot from a light box (or switched receptacle) and "returning" the switched result (whatever the 3-way switches decide) on its other wire. Which wire is the hot and which is the return leg? If it is connected according to Code at the light, the black of two-wire cable-h should be the return leg for the light; therefore our switch-18 is the leg-end of the system and its partner elsewhere is the hot-end; therefore the non-traveler wire in cable-n (that is, the black) is that hot, provided via the white of cable-h from the light.

19- Switch-19 (a 4-way switch) is the middleman of its 3-way system, but now using 2-wire cables instead of the 3-wire cables of switch-9. No hots, legs, or neutrals are needed here; they are being taken care of in other boxes and cables of the 3-way switch system. Life is simple after all. Travelers in, travelers out; which pair is incoming and which outgoing could be determined but is not usually important, even if instructions from the switch manufacturer seem to say so. If you want more challenge, how would a 4-way switch be hooked up when the two cables were n-n? How when they were t-L-n or n-n-h?

As part of your wiring instruction, a good review now would be to go back and account for what became of six black wires that used to be in the big wirenut in FIG.1.

Figure 3 (Lights) Commentary New window.

1 [L-L]- To run, a light fixture needs a neutral and a switched wire. (Fixtures with pull or twist switches right on them would use an unswitched hot wire, of course.) Whatever else goes on electrically in a light box is to help the switching happen and/or for the sake of other parts of the circuit. Box-1 represents the classic "black-to-blacks and "white to whites" instruction. Fixture-1 itself only needs the black and white from whichever cable-L is bringing hotness and neutralness. The other cable-L is going to another light box whose fixture wants to be switched along with this one. A light box like this might have three or four or just one cable, and the black-to-black, white-to-white idea would apply, as long as we were sure that all these were two-wire cables and that (other than the one bringing neutral and switched) they were all going to other lights, to be switched together. If that were the case, in our minds we could label those cables L-L-L, L-L-L-L, and L... In any case, when there are more than one neutral wire or switched wire for the fixture to attach to, it can be a good idea to pigtail a single extra piece of wire from those wirenuts for the fixture's wires to attach to. That way, whenever the fixture is taken down or replaced, there is less chance of bothering the good connections that were first established. In these light diagrams I have not shown such pigtailing -- to simplify things... [What if the Fixture's own wires are not black and white?]

2 [p-h]- Here, however, we have two flat cables hooked up differently. Why? Well, there is no light but this one that is to be switched, and the neutral is arriving from a cable-p, whose black is constantly hot. So that cable is not coming from the switch -- not able to provide the light's switched wire. Rather cable-h does come from the switch, and its white is not neutral ("h" is for hot-white)! This is a way, more common before 1970, to switch a light when there are a neutral and a hot at the light box. It is commonly called a switch "loop". The hot makes cable-h's white be hot. This same cable-h at the switch's box may have both of its wires attached to the switch's terminals (see switch-2 or switch-12 above), so its black back at our light box is the switched wire we are looking for, to control this fixture. Could cable-p's black just as easily wirenut to cable-h's black, with cable-h's white serving as the switched wire (to hook to the fixture's black wire)? Functionally, yes, but that is against Code, because then you would have a confusion whenever the fixture was being replaced. Namely, which white wire is which for hooking up correctly to the fixture?... One rarer use of cable-h from a light box is shown in switch-18 above. There the end result for the light is the same, but instead of a single switch handling the wires, a 3-way switch system works on deciding the on- or off-ness of cable-h's black at our light.

3 [p-f]- Box-3 shows an additional non-white wire in cable-f, so we don't have to use its white to get hotness down to the switch. But why does the switch box need a neutral to be sent down to it? We don't know, but maybe that box has another switch in it, wired more like light-1's switch, that needs a neutral. Or maybe that switch box is going to pass the circuit's hot and neutral both along to enable a nearby receptacle... Although I have spoken of cable-p as the source of neutral and hot in this box, you would see the exact same connections if cable-f were the source. In that case, hot and neutral come up from the switch box in cable-f and are passed out by way of cable-p to somewhere further on the circuit.

4 [p-p-f]- Add another power cable. Which of these three cables is bringing hot and neutral to this box? It doesn't matter. The circuit's power is passing through the box in any case, and in the process delivering neutralness and a switched (red) wire to the fixture.

5 [p-L-f]- Box-5 lets us see a combination of the principles from box-3 and box-1. One two-wire cable (L) feeds neutral and switched black to the next light. The other (p) gives/gets neutral and hotness to/from the light's switch box, for the sake of other parts the circuit.

Figure 4 Commentary (Compared to Fig.3 Above) New window.

6 [p-h-p]- These connections are functioning as they do in box-2, but with the addition of a another cable-p, which can be a recipient or the source (this time) of circuit power. The red tape or ink on cable-h's white wire is to remind anyone installing this wiring that Code now requires this sort of re-identification of all white wires that are not neutrals. I show most of them as still white because that is what most people visiting my website will be finding in their homes. In fact, if you have a newer home (this century), realize that the underlying color of some of your red- or black-looking wires may be white.

7 [p-h-L]- Like box-2, this one has a switch loop going down to the switch, but the added cable now is for a second light to be switched with light-7.

8 [p-h-p-L]- Here we combine the ideas in boxes 6 and 7 by adding a fourth cable. So what is going on here is the circuit's hot shared among the p-cables and the white of cable-h; the circuit's neutral being shared among p-cables, the fixture, and outgoing cable-L; and the switched black from cable-h being shared to the fixture and cable-L. In other words switch loop "h" returns switchedness to control not only this light-8 but another light fed out on cable-L. You might test your understanding of the wiring connections we have been dealing with by diagramming for yourself two more similar sets of light box connections: p-p-p-h and p-L-L-h.

9 [p-p-L-f]- Three 2-wire cables with one 3-wire cable in a light box may be functioning as I am showing them here. This is actually the same as box-8, except that cable-f's added wire lets a neutral be brought from or given to our light's switch box, for other purposes. But other functions for three flat and one round cable are possible. If you have grasped the principles shown in boxes 3, 4, 5, and 9, you ought to be able to diagram these others: p-p-p-f and p-L-L-f.

10 [f-f]- Box 13 will be giving the only scenario other than this one, for the connection of only two 3-wire cables at a light box. Here at box-10, the circuit's hot and neutral are being passed through from/to a second light box whose fixture will be switched along with ours via the red wire. At that box there will probably be one or two 2-wire p-cables passing power between that box and more things of the circuit. The arrangement of box-10 is not common... What would happen if someone goofed and connected the fixture's black to the other blacks?

Figure 5 Commentary New window.

11 [L-m]- Don't worry, I am expecting no double circuits at light boxes. I don't remember ever seeing that, but I suppose it is possible. No, box-11 shows cable-m switching multiple items. Well, two really -- our light and whatever cable-L is going to. It could be another light. It might be a separate fan. Cable-m's red is a switched wire from one switch and its black is switched from a second switch in the same switch box. See switches 4 and 5 in FIG.1 above. If this box-11 were for a ceiling "paddle" fan assembly that included a light, and if those two were to be switched separately, then this diagram would generally apply. But instead of there being any cable-L at all, the black of cable-m would be connecting to a black of the assembly. There might be two whites from the assembly or just one; either way, they would wirenut to cable-m's white. Similar attachments would be made at a combination exhaust-fan and light unit that was to have those functions switched separately; this would be common in bathrooms.

12 [L-p-m]- Box-12 is somewhat similar to box-11, but instead of a switch box sending the neutral to this light box, we have it provided here by cable-p. The white of cable-m is now made to be a hot, taken from cable-p and attached in some fashion in the switch box to at least the two switches that control fixture-12 and cable-L. See the switch end of things at switches 14 and 15 in FIG.2 above.

13 [t-n]- Not even an electrician recognizes the connections in this box immediately. Knowing that the light is part of a 3-way switching system helps. Two of the wires of cable-t are travelers "tying through" our box to the two travelers in cable-n. Cable-t is coming from a 3-way (and any 4-way) switch that is on the "hot end" of the system; it is also supplying the neutral path for our light. Cable-n is returning the on-off verdict from a 3-way (and any 4-way) switch on the "leg end" of the system. See switches 16 and 8 in Figures 2 and 1 above and 3-way diagrams. Cable-t must use its red and black wires as its travelers because the white wire is set as neutral. Cable-n could not have used its white as the switched leg, but theoretically it could have used its black as one of the travelers, with the red switching the fixture... How would an additional light be fed out from this box and be controlled along with this fixture-13? In other words, how would you hook up wires in a light box with t-n-L cables?

14 [p-n-n]- Once again we are dealing with a light controlled by a 3-way switch system. But here the neutral, and even a hot for the 3-way system, are provided by the new cable-p. So the white wires of both n-cables are not going to be neutrals. The only color restriction on these n-wires is that the returning leg that will attach from the right-hand cable-n must not be white. So cable-p's black could have been wirenutted to any one of the wires of left-hand cable-n, with the other two being travelers. Actually, we could have hooked cable-p's black to a wire of the right-hand cable-n, making it the hot-end cable, as long as we then treated the left-hand cable-n as the leg-end, hooking its non-white non-traveler to the fixture's black. The 3-way system would work either way. How would you deal with connections at this box if an additional light to be switched with this one were now fed by a 2-wire cable? That would make the box's cables p-L-n-n.

15 [p-p-n-n]- With box-15 we do add a 2-wire cable to the previous example, but it is not for adding another light. It is to pass the neutral and hot of the circuit on to some other needy box.

Figure 6 Commentary New window.

1 [p-p]- This receptacle-1 presents perhaps the most common hookup to be found in outlet boxes. One cable-p (which one doesn't matter) is incoming power that is, a black hot wire and a white neutral. The other will take power out of the box and on to the next item of the circuit, once it receives that power by some connection to the wires of the incoming p-cable. In this case the receptacle's terminals -- side-screws and/or push-in-the-back holes -- provide a way for that to happen. Blacks attach to the brassy side and whites to the silvery side. In the process, the receptacle itself can now also pass power to what we plug into it.

2 [p-p-p]- Here a third power cable is present. Of any number of p-cables and/or f-cables, one will always be the source of hot and neutral, and the others, if any, will depend for their "powerness" on their connection to that one... Box-2 is mostly to show that, given the functions the wires are meant to play, there are often still many options for how to make the electrical connections. The two blue wirenuts in box-2 are "pigtailing" wires to the receptacle. As you can see, wires not involved in a pigtail can still make their connection at a receptacle screw or hole.

3 [p-p-p-p]- This next outlet shows that some receptacles have enough terminals for the wires of all the cables a box is allowed to be filled with. Most single-gang boxes are not supposed to have more than four cables, if that. Some receptacles have terminals for connecting only two hots and two neutrals. Others may have enough screws and holes for six hots and six neutrals, but in a single box this would not be needed.

4 [f]- At receptacle-4 we get our first look at a 3-wire cable in an outlet box. This is a case of a switched wire being fed with hot and neutral in the same cable. There is something else new to notice here -- right on the receptacle. If it looks like this receptacle is missing a gold tooth compared to the ones to its left, it is. What is missing is not a terminal screw, but a metal tab that is responsible for passing hotness between the top and bottom halves of these "duplex" receptacles. It is also there so that we can keep the two halves from being connected if we want -- by breaking the tab off (back-and-forth motion with needlenose pliers). Why would we do that? Receptacle-4 is set up to be a switched receptacle. Or I should say, half-switched. By convention, one use of the red wire from 3-wire cable is as the switched "leg" -- for a light or for a receptacle. The black is constantly hot. This red will only be hot (live) when the switch it comes from says so. What would happen if we had these wires hooked up here at receptacle-4, but we didn't break the tab off on the hot side? (People do this, when replacing receptacles blindly.) The constant hotness of the black would carry the day -- the red would have no effect. In fact, the red would be made to be constantly hot. So the switch across the room would do nothing, and no matter which half you plugged a lamp into, the lamp would stay on all the time (except for the twist-switch right on it). By the way, you are not at all likely ever to need to break the tab off from the neutral side of a receptacle. So don't do it. It could disrupt the circuit from that point on.

5 [p-f]- This receptacle is also being switched. This time it is the top half that is switched. There is no rule saying to switch one half versus the other, but if other outlets in the room or the house are switched a certain way, following their lead makes sense. This receptacle-5 also has an additional 2-wire cable. Cable-f at box-4 brought a neutral and a hot to that receptacle. Here at box-5 it could be the same way, or the power might be coming in on cable-p and passing to the receptacle and (on cable-f) toward the switch box, with the red still coming "back" here. Although I show the hot-wire connections as a pigtail, the black wires of cable-p and cable-f could have both attached to terminals at the bottom of the receptacle's hot side.

6 [p-p-f]- Receptacle-6 is back to having the bottom half switched. At this box, another 2-wire cable has been added, sending power to more of the circuit, probably to another outlet, one that is not to be switched. I show all three blacks pigtailed to the terminal. If only two hot-side terminals were available at the top half, we would be forced to pigtail from at least two of the three blacks. On the neutral side, we could have pigtailed, but enough terminals were available to attach directly to them; both top and bottom of a switched receptacle are available for neutrals to attach to.

7 [d]- Notice that receptacle-7 is hooked up just like #4. (The position of the white wire connection doesn't matter.) This #7 is not a switched receptacle, however. It is a receptacle whose top half is from one circuit and bottom from another. The circuits share one neutral and are from two circuit breakers, which are 240 volts apart! Since 1981 Code has wanted those two breakers physically tied together so that no one working on the receptacle could think it was dead from turning off just one breaker. Where would such a double-circuit receptacle ever be encountered? Dining/Kitchen receptacles in the 1960s were often wired this way (see 2-circuit); receptacle-7 would occur at the end of such a run. The only other case of a double-circuit duplex receptacle would probably be for two special appliances located together and each getting a circuit dedicated to it alone. Two freezers perhaps. Or the pump and the heater for a whirlpool tub.

8 [d-p]- Here is another case of the 3-wire cable bringing two circuits to the box. In this case, the receptacle is only being run by the black circuit. The red circuit is tied through to feed cable-p, which may go to many more items. The black circuit here seems to be serving only receptacle-8, however; this is not as common as what will be shown in box-18. Notice one other thing. The neutrals of box-8 are pigtailed to the receptacle. Up to now, we have had the option of attaching neutrals directly to the receptacle, but where a double circuit is involved, it is important (and Code) for the neutral connection for the two circuits to be independent of the receptacle. This more reliable connection makes a loose shared neutral -- a condition that allows sustained high voltage to damage electronics and appliances -- less likely. See Double circuits.

Figure 7 Commentary (Compared to Fig.6 Above) New window.

11 [p-h]- Two flat (2-wire) cables at an outlet are rarely meant to do what is going on here, but maybe you should be made aware of the possibility. The white of cable-h is hot -- made hot by the black of incoming cable-p. Why? Notice that this is a receptacle whose lower half is switched by the black of cable-h (coming back here from a switch across the room). So if the room this outlet is in has no overhead light, and this half-switched receptacle is being replaced, hooking it up as if it were like receptacle-1 (without breaking the hot-side tab) would return cable-h's black's hotness (when you turned the switch on) on its white onto the neutral side, making the circuit's breaker trip immediately.

12 [p-p-h]- This one is like #11 but with an additional cable feeding the circuit out to something else. What makes receptacle-12 even rarer, though, is that the whole receptacle is being switched (found mainly in 1950s homes). More often the two-wire cable "switch loop" would be switching just half the receptacle, and a pigtail would probably used be used to join two blacks, one white, and the hot-side always-hot-half terminal. See box-13 (next).

13 [p-p-p-h]- This one adds one more outgoing p-cable and shows just one half of the receptacle being switched again. Not common either.

14 [f-f]- The more common way of switched half-receptacles is shown here. Unlike #4 above, here we have two 3-wire cables. We might like to think of one as incoming and the other outgoing, as we do with 2-wire cables. It is true that both constant and switched hot wires are receiving and/or passing on their form of hotness to another outlet box. But it can be that the black of one cable might be incoming while the red of the same cable would be outgoing! (And vice versa for the other cable.)... This would be a good place to mention something about two or more outlets of a room being switched like this. If a person replaced receptacles without regard to their being switched and then found that the switch can no longer turn a lamp off, they will not be able to solve the problem by finally breaking the hot-side tab off the receptacle they were used to using for their one lamp. The other receptacles that used to be switched (though the person didn't use them) would all need their tabs broken off too, so that blacks would not keep reds hot all the time. Either that, or the person could remove (and wirenut together) all reds from receptacles they do not want switched.

15 [p-f-f]- (Assume that this one is not a case of a double circuit doing something odd.) This demonstrates all the principles involved with #4, #5, and #14. But what is the dotted red? An outlet box that has two 3-wire cables is sometimes itself not switched at all (the tab is not broken) and the two red wires in the box are simply be wirenutted to each other and do not connect to the receptacle. This would have been a convenient way to get the switching wire ultimately to a receptacle elsewhere that is the one meant to be switched. Or it might be to give the homeowner some versatility for determining which outlets (out of all that have these red wires in their boxes) will end up being switched. Different furniture layouts may call for different outlets to be switched. In answer to the question, then, the dotted red line means this could be a half-switched receptacle (with the red line solid) or it could be an unswitched receptacle that has the potential for being switched with an added wire to the receptacle (and a breaking of the tab).

16 [p-p-h-f]- Before reading on, you could consider this one as a midterm test: tell yourself what is going on here. ...
Right -- all the principles in #4, 5, 6, 11, 13, and 14 are happening here. Cable-h is a switch loop, so its white is given hotness, but the switched black that returns does not end the story. It passes its switchedness on to the red of cable-f. So in this example, this black should not be attached with the other black but with the red, as shown. How would you diagram a box with cables identified as p-h-f? How h-f?... It would be possible for three 2-wire and one 3-wire cables not to involve a switch loop like this (an h-cable, in other words). Such a box would have its cables identified as p-p-p-f. It would still be housing a switched receptacle. Unless, of course, it were a case of a double circuit -- along the lines of #8 or #18 (coming soon).

17 [d-d]- The double-circuit outlets common in kitchen and dining rooms of 1960s USA homes would typically pass their two circuits along together from box to box using 3-wire cable. By virtue of serving the kitchen, these would have been 12-gauge cables ("12-3"). In Canada they have been able to be 14-gauge and are still commonly installed to meet a Code requirement. In both countries neutrals needed to be pigtailed for the reason given regarding receptacle-8. Where people have replaced such receptacles without breaking off the hot-side tab, they create a 240-volt short, though they may not realize it (see Double circuit). By now Code calls for many kitchen outlets to have GFCI protection. But GFCI-type receptacles and their load receptacles can't get along with a double circuit. So when any of these "split-circuit" receptacles are replaced now, either a two-pole GFCI circuit breaker may have to be installed in the panel, or the receptacle may have to be converted to using just one circuit or the other, as illustrated somewhat in #8 and #18.

18 [d-p-p]- Here the #8 box is given an additional outgoing cable, so that both circuits continue beyond this box, not just one. This receptacle-18 is not set up to be a double-circuit (a.k.a. "split-circuit") receptacle, so no tab is broken off. The arrangement shown here is a common one for the first box that a two-circuit cable from the panel arrives at. Although all the neutrals could have been pigtailed, only two are required to be, in this case -- the shared one (in "d") arriving from the panel and the one going out with the circuit that is not connected to this receptacle. If the neutrals attached to this receptacle-18 were loose or purposely detached, the red circuit would continue to work properly and could not bother the black circuit with odd voltages. See Two-circuit cable.

A chart to determine the limited possible hookups for your type and size of box, given the number and type of cables that come into it. New window

Understand the chart and its limitations:

• Each line in each cell represents a possible combination of wire functions for those cables in that particular box.
• No one combination is much more common than the others in a cell, except: any with an asterisk -- * -- are less common than those without an asterisk in that cell.
• Not every possible combination is shown, only all the ones I could think of that were not an extremely convoluted or rare way of wiring. What I have done is eliminate all the combinations that make no sense. For instance, a 1-gang switch box with two 2-wire and one 3-wire cables shows four possible combinations of wire functions involving p, f, L, t and n uses. I have already counted out (as senseless) other combinations of those letters, as well as every use of h, x, m, or d, because they would have had no use in relation to a single switch in a single box.
• For a given combination, there will occasionally be more than one way to hook things up. As an example, which light leg is controlled by which switch will sometimes be a question.
• The chart only shows results for standard boxes containing one receptacle, or up to three switches, or one light. More receptacles or combinations of receptacles and switches are not shown. Nor are duplex switches or a switch-and-receptacle device.
• It does not take into account an electrician's use of a box for spare or future-use wires, or junctioning that has no relation to the items installed at the box. These will be rare.
• Cables that should (or might) attach to a 4-way switch are shown by the "+" between them being bolder.

How to use this Cable-and-Box Chart

1. In the chart, find the number and type of cables in the box you are working on.
2. Look across from there to the type of box it is. Pick the first line listed. Then...
3. Look up that combination's code letters in the Cable-and-Wire Functions Chart above. If the meaning of your letters makes no sense for what you already know about the switches, outlet, or light you are dealing with, look up the next combination listed in your cell of this chart below, until you find one that seems likely.
4. Now try hooking up according to the wire uses of those cables, with help from the references in that chart, from the house wiring diagrams above, and from section "4" below.
5. If your hookup does not work much, try any alternate hook-up that would match those same uses, and then go on to consider and try out the next combination from this chart below. If your hookup almost worked perfectly, try minor changes one at a time.
6. If you are still stumped, for $15 you can have me help. First fill out the Request form and pay. Then I will probably suggest that, if possible, you draw up a diagram and description of everything you know about your circuit and box(es) and email these to me, along with any photos. And we'll go from there.

A FEW CAUTIONS                        New window.

Safety. Until you need power on to make tests or try operating something, having the relevant circuit breakers off (or all breakers off) will put you out of harm's way.
Multiple Circuits. Expect to find more than one circuit present at some switch and outlet boxes, even single-gang boxes. Discovering this not only helps you be safer, it actually helps you understand what is what in those boxes. If more than one circuit is present in a box, their sets of neutrals should probably be kept apart from one another -- unless the two circuits arrive as a 3-wire cable (sharing a neutral), in which case the neutrals of both these circuits need to be wirenutted together.
Meters and Testers. Prefer logic and controlled experimentation, over testing with a meter. Holding a voltmeter or ohmmeter in your hands, you might imagine that they will tell you a lot. There are tests that can be done on a perfectly functioning home that neither you nor I would know how to interpret. How much less confidence should we put in testers while some electrical connections are in doubt or missing! It is usually all we can handle to try out our existing lights and outlets as the acid test of whether we are on the right track.
Documenting. Unless your memory is a lot better than mine, prepare to write down details of how wires are now, what you plan to do to them, what you then actually do, and what the result is. You might even record your conclusions, in case they should be re-examined later.

IN GENERAL

Don't Panic. If you have caught an undoing of wiring connections early (even several connections), you may need to apply only one or two principles to make your way back into working order. Use what is still intact as an asset, as clues for the few possibilities that need to be tried out now. To what extent have connections been changed? Removing a switch or light doesn't usually bother anything but the one light or set of lights involved. And removing a receptacle, though it very often affects the circuit from that point onward, does not tend to leave any problem once you put the new one in right. If this sort of replacement is all that has been done, it may be that Upgrading is all you need to read. Otherwise, read on. If a person has dug deeper -- in order to fix a circuit problem or trying to rewire something in the area -- then it may be harder to determine how to get things working properly again. Various wirenuts may have been removed without keeping careful track of which wires were together. Still, use what remains as it was, as help in the restoration process.
See the Clues. In general, wires that are together or seem to have been together (physically, not judging by color) can be considered as clues to their function and the function of other wires. One thing you might want to observe and write down before changing anything is: which wires and even ends-of-wires show signs of having been twisted together with others (they might go back together); a curled wire-end was probably attached under a switch or receptacle screw.
Notice Cables. Always remain aware of the cable a given wire is part of. The wires in each cable will be performing only one of the functions shown in the Cable-and-Wire Functions Chart. Each cable is coming from ("going to" means the same thing) another box somewhere. These other boxes can be opened, their wires perhaps tested, or their undisturbed connections simply read. The Cable and Box Chart may also help you limit the number of hook-up possibilities you might have to consider.

REVIEW COMMON HOOK-UP PRACTICE AND RULES

Switches. Not counting green terminals or wires, single-pole switches have 2 terminals, 3-way switches have 3, and 4-way switches have 4. For many dimmer and specialty switches, these terminals are in the form of wires that are part of the switch. Otherwise the terminals consist of screws and/or holes, which sometimes allow more than one wire to attach there. Some holes may hold onto the wires automatically (they theoretically release by a small screwdriver being inserted in a separate opening nearby). In other cases, holes only secure their wires when the screw is tightened down. A screw itself is designed to hold only one solid wire directly under it, curled clockwise.
Screws are generally brassy in color, but one of the terminals of a 3-way switch (the "common") is a different color, usually dark, and a 4-way switch has two brassy and two of another color. Many 3-way dimmer switches have wires instead of screw terminals. Any pair of 3-way switch screws or wires, that are the same color as each other are for a traveler pair to attach to. The third (odd-color) screw or wire connects to the common wire (that is, to a hot or the light-leg). See 3-ways.
A jumper is a short piece of wire within a box, going between two wirenuts or between two devices' terminals. It simply passes a function (hot, switched, or neutral) from the one place to the other. A pigtail does this too, but only goes from a wirenut to a device. I mention jumpers here to alert you that hot-wire jumpers that had been used originally between switches may have been discarded with the old switches. If so, some lights or other parts of the circuit will no longer work, and you would have to restore such hot connections in some way, not necessarily using jumpers (use pigtails).
Receptacles. What is said above about the terminals of switches is true of receptacles, except that the brassy screws on one side are for the hot or switched wires, and there are silvery screws on the other side for neutral wires. Be aware that each side of the common ("duplex") receptacle has removable metal pieces at these terminals, which are electrically connecting the top and bottom halves of the receptacle and their top and bottom terminals.
Lights. Lights that mount onto the ceiling or wall surface come with a white and a black wire (or sets of whites and blacks) to be attached by wirenuts to the appropriate neutrals and switched wires at the light box. Be aware that circuit wires unrelated to running the light may be present in the box. A recessed light has its connections in an integral junction box that is accessible from below, with a little trouble.
Ground Wires. I do not mention grounds (the bare or green wires) except here. Generally they all should be combined with each other and with added pieces that will terminate on each receptacle or switch that has a (green or bare) ground screw or wire. If you know some grounds in a box were not together before -- when things were working -- don't put them together yet; for the sake of your functionality problem, they should not matter. On the other hand, you may want to find if one of them is a reliable ground, in case you will be testing for voltage later on.
Wire Colors. Remember that non-white wires are not neutrals, and neutrals are white, but this does not mean every white wire is a neutral. In fact wires I am calling "white" on this page may already have been designated as non-neutrals by tape or ink, and doing this to non-neutral white wires would bring your wiring up to current Code. Still, for our purposes here, always notice which wires were white from the factory, regardless of their appearance now; these are what I am calling white. With all this said, it remains true that true neutrals are never to be switched, though they were sometimes in the 1920s or 1930s.
Position in a Box. The position of a cable in a box, from right to left, may correspond somewhat to which switch it relates to, but do not rely on this. The same holds for whether a cable comes into the box from above or below -- a ceiling light cable (leg) might tend to come in from above, but not always.

KNOW YOUR SITUATION

Realize What You Already Know. Review in your mind how the various switches, lights, and receptacles in the area had related to one another. Was a fan-light controlled by one or by two switches? How many total switches controlled each set of lights in the area? Consider whether some outlet might have been switched.
Look Behind the Scenes. In any box you are dealing with, loosen the switches, receptacles, or lights there (and at other boxes of the circuit, nearby or related by switching) enough to view how many cables of what sort (2-wire vs. 3-wire) show up at all these boxes.

READING WIRENUTS AT SWITCH BOXES It will be up to you to apply the principles of this tutorial to your situation, but the status of existing connections at a switch box may help you, as follows.

Setting up single-pole switches. If any white wires are wirenutted to other white wires (without other colors in those wirenuts), they are probably neutrals and in any case should be left as they are. Each black and each red (whose black mate is in a wirenut) that are not in a wirenut and whose white mate is wirenutted with two or more other whites, is probably to be switched and will attach to one terminal of a single-pole switch. Each black bundled in a wirenut but that does not "leave" the box in a cable, is probably to be a hot and each one will attach to the other terminal of single-pole switches.
Setting up some 3- and 4-way switches. If it is known that a box is to serve a 3-way switch; and there is a 3-wire cable entering the box, and its white wire is wirenutted to other wires and its black and red wire are not, then the black and red of such a cable are probably to be travelers and will attach to the same-color terminals of a 3-way switch (in either order). (If there are two such 3-wire cables that meet this description and their whites are wirenutted to each other only, they are probably for a 4-way, not 3-way, switch that will have black-red pairs attached, one pair to each same-color pair of terminals.) The common terminal of 3-way switches will receive either a light-leg black (or red) or a hot wire, which is often a black piece coming from a wirenut containing several blacks.
Setting up other 3-way switches. If the white wire of any 3-wire cable was not wirenutted to any other wires, and its black and red mates are likewise free, then these three should probably hook to the terminals of a 3-way switch. There are only three ways this would have to be tried, namely, with each wire taking a turn under the "common" screw. But duplicating the traveler colors used at the traveler terminals of the other switch of the 3-way system may work immediately.
Keeping obvious circuits apart. If there are two or more bundles of white wires in a box, and if none of the black mates of the whites-in-one-bundle are wirenutted to any black mates of whites-in-another-bundle, retain this isolation, treating these as if they are from different circuits. An electrical trainee doesn't always realize this.

START FROM SCRATCH?

Whether to Start Over. If a lot of connections have been undone, and the charts and diagrams above don't help you make heads or tails of things, it may be best to separate all the wires in the box and start from scratch. In general you would then want to see which wires bring hot and neutral (if any) into the box. You could then start experimenting with one new connection at a time, to discover what is affected elsewhere in the house and therefore what the likely function of that new wire is meant to be. Turning power off again at each step makes sense; since you don't know what your new connection will do, you don't a short circuit possibly blowing up in your face.
Experimenting. When putting a box's wires back together from scratch, it is usually easy to tell which one cable (or more, if more circuits are there), if any, brings power to the box (the incoming p-cable or f-cable) -- just test between its black and white with a light bulb or voltmeter. But, particularly at switch and light boxes, it is harder to find which cables (if any) are passing the circuit on (outgoing p-cables or f-cables). Even at outlets, the remaining cables aren't always outgoing; once in a while an h-cable may be there. So the only sure way to identify which cables should hook up their whites as neutrals and blacks as hots, will be to hook candidates up one at a time and see the effect this has on the rest of the circuit. If you unknowingly hook up an h-cable in this way, nothing new downstream will be enabled (and one light may run unswitchably or one switch may trip the circuit's breaker). (By the way, if a short is passed through a dimmer switch, sometimes this will hurt it, so for the sake of experimenting, if you can use a standard switch there temporarily, do so.)

HELP FROM THE CIRCUIT DETECTIVE

I may be able to help you remotely. Any photos, diagrams, and descriptions you send will help. We might have to go through a process of experimentation or testing, but I will be at least as persistent as you are. Contact me in the normal fashion.