First and foremost, you should constantly be aware of which cables may constitute a safety risk. A hot wire is always black, red, or white, with black or red tape around it. While white wiring is permissible (when properly identified with black or white tape), using any other color for a current-carrying wire is generally discouraged.
In most homes, all the wiring inside the walls is done with black and white wires. These are called "commons" or "paired conductors", meaning that each conductor within the cable is the same material (copper) and has the same potential. If you were to connect one end of a voltmeter to one of these colors, it would read about 120 volts. If you connected both ends of the voltmeter to both colors, it would stay at 120 volts because there's no VULNERABLE spot where either color might have voltage on it more than another - they're equal partners in carrying current so there's no way for them to be unequal. Unless one conductor gets damaged - maybe by being abraded by some metal inside the walls.
Then this conductor begins to break down while the other one keeps on going, so voltage now begins to show up on the formerly healthy wire.
In many forms of switch wiring, the hot wire can be a variety of colors, however the neutral and ground wires should always be the same. If you are doing any house wiring, accurate wire identification is critical so that you make the correct connections. Amazon is a great place to get home wiring supplies. Wire color codes are usually listed on each package of wiring insulation. Know what the various colors mean and you'll be able to match them up correctly.
These are the most prevalent electrical wire colors. Remember that black and red wires are usually hot, indicating that they are source wires carrying electricity from the electric service panel to a destination such as an outlet or a light. White or neutral wires are always safe to touch. Yellow wires should not be touched unless you have a reason to believe they are not part of any circuit.
The term "circuit" means all the wiring in a house that returns current to the panel on either regular voltage or high voltage. A circuit may have only one conductor (as in a straight line from the panel to an outlet or light fixture), or it can have multiple conductors (as in a looped circuit). If you're not sure which wires are which, just remember that black is always source and white is always drain. If you were to connect both ends of each conductor, you would have a complete circuit between the source and the drain, allowing power to reach its destination.
Source and drain wires are often called "hot" and "neutral", but that's just terminology. Any conductor could be a source or drain, depending on how you connect them up. The important thing is that you know which ones are which at every junction in your home.
The terms "live" and "dead" also refer to the presence of voltage on a conductor.
Black represents heat, white represents neutrality, and green represents ground. However, if you need to rewire a light switch or a plug socket, you may run across two black wires on occasion. Before you proceed, you must establish which black wire is hot. You do this by finding out which one causes the circuit to break when you touch it. If they're both live, then you'll have to replace them with only black wires.
Once you know which is hot, you can try to connect it up in some way. For example, you could connect both blacks to a new piece of metal tapered down to fit into the hole of the fixture, and then screw that into the wall. This would make both blacks dead while the old ones were still live. Finally, you'd need to check each wire at the breaker panel to make sure it has been changed over to the new connection.
This is just one of many things you should know before working on your house's wiring. If you're not sure who does home repairs where you live, ask your local utility company or hardware store owner. They may be able to help you find someone who can.
Home repairs can be expensive, so make sure you hire someone who has experience doing work like this. But if you don't, you might end up with an expensive mistake that needs to be fixed by a professional.
Only white (or grey) for the neutral power wire and bare copper, green, or green with a yellow stripe for the protective ground are required by the US National Electrical Code. In theory, any color other than these may be used for the power wires. In practice, only red for voltage and black for current are commonly used.
The code requires that if you're working with old wiring, you must first try to determine what the original colors of the wires were before they were disturbed or altered in any way. This is called identifying the hot wires. If you can't identify them, you have to assume that you have whatever colors are currently on those wires.
You should also check for damage to the insulation on both sides of each wire. If there are open circuits, short circuits, or frayed or broken insulation anywhere on the cable run, this needs to be repaired before you continue working on it. Otherwise, you might get hurt.
Once you've identified the hot wires, you can start matching them up with the corresponding wires going into various boxes or terminals. Power lines are usually very stiff so they won't bend unless there's a gap where two cables come together. Then they'll cross over each other like a bridge until the gaps end.