This article provides some basics on how residential wiring is used and connected together. See the information below for tips and tricks on how to install and modify the wires in your home.
Not sure if this is your problem? See the aticle 'Troubleshooting Wiring Problems' and 'Do It Yourself Electrical Repairs' for listings of all the electrical topics.
Most of the information in this article has to do with what you find inside of a box when you remove a device. What are all the wires for? Which ones are hot? Will something stop working if I unhook something? All good questions, the subjects below will address these concerns.
For most homes in the United States, the power is 110/220 volts. You will sometimes see other designations, like 120/240 or 115/230 volts, why is that? Electrical devices are designed to work with a range of power. The reason is that you have both a design voltage and a maximum voltage. Design voltage for most devices is 115/230 volt. Devices can work with plus or minus 10% of those figures. So a typical outlet may have as little as 104 volts going to it and everything will still work fine.
The higher number is the combined total of the two hot legs of power that feed your panel. When have one hot wire, it is hooked to one side of the panel and provides 115 volts +/- of power. When you have two hot wires, the voltage is doubled, 230 volts +/-.
When you work on a box that has cables coming into it. The number of hot wires in the cable, should tell you what type of power you are dealing with. One black wire would normally be 115 volt, a black and a red (usually red, or another color) would mean 230 volt.
Residential wiring will usually only have three colors of wire, plus a bare ground wire. Unfortunately, the use of these wires is not always self explanatory. As an example, a electric hot water tank can be wired with 10-2 w/Ground wire. The white wire will be one of the hot legs for the 240 volt hot water tank (Note: Most codes do not allow for this method any longer.
Working With Electrical Items
Using Wire Nuts
Braiding Ground Wires
The white can also be a traveler (meaning it is hot sometimes) in a three or four way light switch. Inside the panel the white wire will usually be hooked into the neutral bar. The exception would be when it is uses as a hot lead. Then it would be hooked to a lug on a double pole breaker. Most electricians will put black tape or a black mark on a white wire that is used as a hot lead. Not always, use your voltage tester to verify what is hot.
Usually, black and red wires are hot. The exception to this would be in light switches, where they may or may not be hot depending on the position of the switch. For three and four way switches the white, red or black could be hot depending on the switch positions and the configuration of the wiring.
Confusing? It can be. In the panel the black and red wires are usually hooked to lugs on the breakers. You see some weird things out there, that is why I use the word 'usually' so much. In other words, some people engage in basic house wiring modifications without checking things out first.
The ground wire should never have a load on it. Sometimes it can act as a neutral, such as the hot water tank wiring mentioned above. In the panel the ground wire would either be hooked to the ground bar or the neutral, if it is acting as the neutral.