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 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.