Black electrical wires transport current from the power source to the outlet and are utilized in all sorts of circuits. Black wires are never used as a ground or neutral line and are only intended to supply electricity to a switch or outlet. If you were to connect one end of a voltmeter to a black wire, it would read about 120 volts, because that's what other outlets on that circuit panel are reading.
The black wire is usually the longest conductor in the cable and can be up to 10 feet or more in length. It transports current from the breaker box to the various outlets attached to it. The white wire is generally shorter, usually between 3 and 6 inches, and carries current from the breaker box to the main body of the home or office building. The red wire is always the third smallest wire and functions as a return path for current flowing into any device plugged into an outlet. Return currents flow back to the battery-powered circuit breaker or fuse at the distribution center where they are again redistributed throughout the house or office building.
Cables containing only black and white wires are called "commons" and are used to provide current to parts of the home or office where several outlets are located near each other. For example, two commons may be used to supply current to two separate lamps or appliances that need to have their own unique voltage for proper operation.
The black wire of any circuit should be regarded live at all times. These wires are frequently utilized as a switch leg in all circuits, transferring electricity to switches and outlets. If you were to touch these wires when they are not live, you would get a shock.
The black wire is the return path for current when a device is plugged into a wall socket. In other words, it goes back to its origin at the power source. This is why black wires are always marked with red tape to indicate that they are live wires. Failure to do so could result in you being shocked by an adjacent wire that has been crossed with one of these players.
These cables can be hard to see in dark spaces such as closets or under furniture where they may be damaged or exposed. Make sure that you don't connect anything to them without first verifying that they are not live!
In all circuits, the black wire is utilized for power. The black wire is not a common wire and should never be used as a ground or neutral wire. It is the power supply to an electrical outlet and should always be regarded hot, or live. It is also frequently used as a "switch leg," or the link between the switch and the electrical load. A third wire from the breaker serves as a neutral wire; it's usually white or grey.
The term "common" means shared or dedicated. In this case, the common wire is being referred to as a wire that will share its burden of carrying current with other wires in the cable. Because there are two conductors within each cable, they can carry two different signals without any problem. It is also possible for a single conductor to carry multiple signals if it is done carefully enough. For example, a single copper wire can carry both a DC signal and an AC signal if each end of the wire has the proper connection (called a "plug") for the type of device it is going to. Common wires do not have these special connections made to them; instead, they are designed to be interchangeable with any other common wire in the cable.
Because common wires cannot be broken or interrupted, if one section of a house gets an electrical fire, it may cause all of the lights in that house to turn off even though there is still electricity flowing through the remaining intact wires. To avoid this problem, common wires must be located as close as possible to the outlets they connect to.
Wires in Black Hot wires with a black insulating layer are always utilized as ungrounded conductors or hot wires. Hot wires are used to supply power to a switch or outlet. Black wires should never be used to connect to a neutral or ground. If they are connected, dangerous electricity will flow into your home.
The term "hot" means energized; that is, carrying a voltage. Electricity flows from the hot wire to the next-downstream device or conductor. Neutral and ground wires stay within their own circuit groups at all times. They do not cross over into other circuits unless specifically allowed by law or code. All of the wires within a building are either hot or neutral, but not both.
If you're not sure if a wire is hot or not, try touching it to see what happens. If it's hot, it will burn you; if not, it's not hot and can't cause you any harm.
Some devices require that certain wires be tied together to create a ground. For example, this is necessary for appliances that have metal parts that could touch ground if not connected properly. The National Electrical Code requires that all appliances be grounded. Before you plug anything in, check to make sure that all the wires are still tied together; if they aren't, then connect them before you attach the appliance.