Here is a list of electrical wires: The black wire is the "hot" wire, carrying power from the breaker panel to the switch or light source. The white wire serves as the "neutral" line, carrying any wasted power and current back to the breaker panel. A green wire may be used instead; it is called the "ground" wire and should be connected to metal equipment such as a water meter or steel frame of a house. A blue or red wire may also be used if there are no green wires available. These other wires are usually referred to as "phantom" wires because they appear in most houses but are not needed for normal operation.
The term "hot" means conducting, while "neutral" and "ground" mean non-conducting. Hot wires are always white or black, while neutral wires can be white, black, or gray. Gray wires are neither hot nor neutral, so they cannot be used to conduct electricity.
In addition to these three main electrical wiring types, many homes have several other circuits necessary for appliances such as air conditioners, heat pumps, and dishwashers. These circuits are also known as "third party", since they are not part of the original construction of the home. They must be installed by a qualified electrician and will vary depending on what additional equipment is being used.
The "hot wire" is the wire that conducts electricity to the source. When you open an electrical panel, you'll notice that all of the white wires in the home are normally hooked together on a bus bar, while separate black wires connect to each circuit breaker. That is why it is frequently referred to as "common." There is a common black wire for each circuit.
If you were to connect one black wire from your electric meter to the other black wire at a junction box, there would be no way for your house to know which wire was which. Thus, they are both considered "common."
The term "common" comes from the fact that these two wires usually connect to some part of the structure of your house. In many cases, they will connect to a wall stud or other metal piece of the house where they can share space with other wiring such as a water pipe or gas line. Where there is no metal available, such as inside a wooden wall, they may simply touch and be able to communicate with each other. This is what makes them common - they can all talk to each other even if you put something in between them.
Black wires are used for electrical service because they're the least expensive to install. If you were to use red wires instead, you'd need to replace all of the existing wiring in the home with red wires before you could connect up a new system. That's why common black wires are always used when connecting circuits together.
In a normal 3-way layout, this is a hot wire that delivers energy from the power supply to the first switch. It is often referred to as the "common wire" or the "line wire." This black wire is constantly hot unless the breaker is turned off. If you were to touch these wires when there is no power running to the switch, you would be shocked. The term "hot" means dangerous voltage being delivered to this wire; if you were to touch it when electricity was present, you would be injured or possibly killed.
The other wires in the 3-way switch setup are normally called "switch control" or "supply" wires. These wires connect with terminals on the switch and can be either live or dead. When the switch is not being used, any voltage present on these wires will be delivered to whatever device is connected to them. For example, if a light bulb is plugged into a switch control wire, that cord will get hot because voltage is flowing through it even though the switch may be in the off position.
It's important to remember that all parts of the house network should always be treated as live until they are properly shut off. You must never touch any part of the network without protecting it first with electrical tape or some other method. If you do so, you could be seriously injured or even killed.
The plain (or occasionally green) wire serves as the "ground" wire, carrying power back to the breaker panel and then outside to a rod embedded in the ground. If you were to connect one end of a voltmeter to the black wire at these locations, it would read 120 volts because that's what's left over after the breaker shuts off the white and gray wires.
The presence of a white wire indicates that an old wiring system was used in your home. New homes are always built with metal wiring which carries electricity safely from room to room and door to door without touching anything else. Old houses use aluminum wiring which must be connected to a neutral wire to function properly. If an aluminum wire is not present or if it is damaged, replace the entire house wiring package because it could mean serious trouble for your home if not done correctly.
If you're not sure whether a white wire is really there or not, try tapping into it with a multimeter. Check to see which way the meter spins when you tap the wire—if it's not spinning freely, it means that you have found the neutral wire and can connect one end of a conductor to it to supply power to a light fixture.
Be careful not to touch any other wires with your meter! Other wires may be live, which could kill you.