House Wiring Diagram of a Typical Circuit

To your right is a house wiring diagram of a typical U.S. or Canadian circuit, showing examples of connections in electrical boxes and at the devices mounted in them. You may prefer to print out the text and the image. Or you may want to try this Version with a vertical image or this Version using frames.

This page takes you on a tour of the circuit. The boxes are shown as light areas. The dark background represents the area between boxes -- usually inaccessible -- where the cables containing the wires shown in the diagram run in the ceiling, wall, and floor framing of the home. As you can see, between any two boxes, either two or three wires run, corresponding to two or three-conductor cable. After you have become familiar with the circuit shown here, you can compare it directly with a housewiring diagram that follows the cables between these boxes as they might be routed in the rooms of a home; for this see Floorplan. For a GFI wiring diagram go to GFIs.

Ground wires (bare or green wires) are not shown. Connections are shown either as wires making contact with the side screw terminals of devices or as wires bundled into blue wire connectors. The diagram is not meant as a guide for doing wiring; for example, the white wires connected to some switches here should nowadays be taped red or black. The diagram is more to familiarize you with what you may encounter in existing homes.

NOTE: Where two wires are shown as contacting a single side-screw on a receptacle or switch, this is not to encourage anyone to ever put more than one wire under a screw (they are only meant to take one). Instead, it is just to indicate that the two wires do electrically connect with each other and with the terminal. But this should be done using any combination of screws, back-holes, clamps, and pigtailing with wirenuts -- all within the capacity of each option.

This circuit starts with A4 receiving hot (black) and neutral (white) wires from the main electrical panel -- imagine the panel below the image. A4 passes hots and neutrals to nearby receptacles A3 and A5 by means of their wires contact with the terminals on A4. A3 and A5 are the beginnings of the two main branches of this circuit, and we can identify several sub-branches that are developed beyond them.

Looking ahead, A3 will feed a string of boxes one direction (A2, B2, A1, B1, C2) and another string through B3, C3, D3, D2, D1, C1, and B4. Meanwhile the branch at A5 provides connection out to B5, C5, D5 ,D4, and C4. It also sends power through A6 to B6, C6, and D6. A6 itself also splits power out to A7, B7, C7, and D7.

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Lets follow the sub-branch that goes left from A3. A3 needs to get its hot and neutral connections passed on so that two lights (A1 and B1) can burn -- not all the time, but according to what the switches at A2, B2, and C2 say. A2 is a normal single-pole switch, as seen by its two side screws. According to the position of its handle, it will either let its light (A1) get the hot connection or not; the neutral connection at A2 (a wire connector) is not affected by the switch.

Meanwhile, however, A2s box needs to help the switches at B2 and C2 receive power so they can run their light (B1). These two switches (B2 and C2) are three-way switches, as seen by their 3 side screws. If either of their handles moves, it changes the hots connectedness to the light. This particular set of 3-way switches is set up in this way: B2s switch sends hotness to C2s along either the red or the white (called "travelers") according to which gold traveler terminal B2s switch internally passes its hotness on to from the black terminal. Similarly, the black at C2 will be made hot or not, depending on which gold traveler terminal the switch internally connects it to. This black wire (the "light leg") is the one whose hotness or unhotness will let the light burn or not, so back at B2's box it must be bundled with the black that goes to B1, where the light is. If your house is newer you may find that the white from B2 to C2 has been colored to show that it is not a neutral, and you may also find a white neutral as a fourth wire going from the other whites in B2 to C2; this is in case a fancy switch that needs a neutral is installed at C2.

Lets go back now to the other sub-branch that goes out from A3. It will run a light (B3) and three receptacles (D1, D2, and D3). The light will be controlled by switch B4, D2 and D3 by switch C3, and D1 by switch C1 (switched receptacles!). Heres how. A3 feeds power to the B3 box, where the light gets its neutral connection immediately; but the light's hotness will depend on switch B4, once B4 has received constant hotness from B3 by a wire connector at B3, which also sends hotness on to the rest of this sub circuit on the black going to C3. Dont rush on. And, yes, a white wire is being used as a hot down to B4; thats the way a cable of two wires comes -- black and white. For some time now this white should be colored differently when installed. In fact wiring done under the 2011 NEC code should use 3- not 2-conductor cable to provide a neutral for possible special switches. In that case the switched wire (black here) would be red, the hot wire (white here) would be black, and the neutral (none here) would be white -- connecting with the other whites at B3 but to nothing at B4 unless the type of switch called for a neutral.

See original here:
House Wiring Diagram of a Typical Circuit