The quickest way to identify house electrical wiring is by its color. Depending on where a wire ultimately gets installed, you cannot always rely on the markings printed on the insulation coating, nor will you always be able to read them legibly.
The helpful reality is that you really have only three types of wire to identify: hot, neutral, and ground.
A number of different colors may be used for the hot wire in various types of switch wiring, while neutral and ground wires should always be the same. If you are engaging in any home wiring, proper identification of wires is imperative so that you end up making the right connections.
Before you begin a wiring project, make sure you understand the basics of wiring and the color arrangement of the circuit. With the power turned off, there is no danger of electrocution, but you could still make a wrong connection somewhere and end up with an incomplete circuit.
DISCLAIMER: Before you begin work on the wiring of an outlet, light fixture, fan, or any appliance, always turn the individual circuit breaker off at the main panel. This will cut power to that particular circuit and prevent the risk of electric shock.
Why Wires are Different Color
The wires inside an NM sheathed cable are color-coded to make it possible to identify each one at both ends of the cable and wire correctly. All NM cables contain the basic black insulation and white insulation wires plus the bare copper or green insulated ground wire. In a three-wire cable, there will also be an additional red insulated wire commonly used as the "traveler" in an application such as a two-way switch.
Standard Colors Used for Home Wiring
What follows here is the standard coloring for wires throughout a home. The gauge or size of the wire may change depending on the current requirement of the circuit, but the color is a consistent feature.
The wire that carries the current from the power source to the outlet or receptacle is the hot wire. Whenever you see a black wire, you know it is hot. There are other wires (called travelers) that carry current in more complicated circuits, but black is always hot.
To complete the circuit, the current must return to the power source. It does this through the neutral wire, which is always white.
In some instances, a white wire may be marked with a piece of black electrical tape at its ends. A white wire that has been marked with black means it's acting as a hot wire and is no longer neutral.
Green or Bare
When you see either a green wire or a bare copper wire, you can be sure it is a ground wire. A ground wire is used as a protective measure. Ground wires return fault current to earth ground, protecting the individual from electrocution.
Red wires are commonly found in sheathed, multi-conductor cable. These are called travelers and typically used for two-way switch wiring. Since red wires still conduct current, they are considered hot.
Yellow and Blue
Yellow and blue wires are sometimes used in more complicated circuits. If they are, they are used as hot wires to conduct current between switches and poles. For this reason, they are also known as travelers.
These are the most common colors used. Other color combinations, including striped wiring, may be used for other applications. Not all colors are standardized.