Electrical wire color codes are part of a standard system that tells the user which wires carry a current and which wires are for ground or neutral purposes.
For example, black and red wires (or white wires taped with either of these colors) are hot wires that carry current. Bare copper or green wires are used as ground wires. White or gray indicates neutral wires.1
Understanding the color coding for electrical wiring will help you know the purpose of each wire to keep you safe and your house’s electrical system in top working order.
What Are Wire Color Code Standards?
The United States follows the National Electrical Code® (NEC), a system for electrical standards that includes partial guidance on electrical wire colors. The NEC says that white or gray must be used to identify neutral conductors and that bare copper or green should be used to identify ground wires. Knowing these colors helps you safely identify the type of electrical wire, its purpose, and how it will power an appliance or circuit.1
Color Markings: Cable Sheathing and Wires
Non-metallic (or NM) 120-volt and 240-volt electrical cables come in two main parts: the outer plastic sheathing (or jacket) and the inner, color-coded wires.
The sheathing is a tough outer coat that binds the inner wires together. The color of the sheathing indicates the gauges (or thicknesses) of the wires inside.1
- White: White sheathing means that the inner wires are 14-gauge wires intended for 15-amp service, used often for light circuits and some receptacle circuits.
- Yellow: Yellow sheathing indicates that the wires are 12-gauge wires intended for 20-amp service, typically used for GFCI outlet circuits.
- Orange: Orange sheathing means that the wires are 10-gauge wires intended for 30 amp service for larger devices like water heaters, air conditioners, or dryers.
- Black: This is typically used for even larger devices that require 40 amps to 60 amps, such as ranges, air handlers (with electric heating elements), or to sub-feed a sub-panel.
Printed numbers and words on the sheathing tell you the number and the gauges of the wires within the sheathing.
Wire Color Codes
Within the sheathing is a different set of wire color codes that has another meaning: the wire’s purpose and, incidentally, its potential danger. Wire color codes are black, red, white, bare copper, green, white or gray, and blue or yellow.1
White, gray, bare copper, and green are the only wire colors that the NEC mandates must indicate a specific purpose. White or gray must be used for neutral conductors. Bare copper or green wires must be used as ground wires. Beyond that are general, industry-accepted rules about wire color codes that indicate their purpose.1
Black Wires: Hot
Black insulation is always used to designate hot wires. This is commonly found in most standard household circuits.1
The term “hot” is used for source wires that carry power from the electric service panel to a destination, such as a light or an outlet.1
Even though you are permitted to use a white wire as a hot wire by marking it with electrical tape, the opposite is not recommended or allowed. In other words, do not use a black wire as a neutral or ground wire, or for any purpose other than for carrying live electrical loads1.
Red Wires: Hot
Red insulation is used to designate hot wires.
Red wires are sometimes used as the second hot wire in 240-volt installations. Another useful application for red wires is to interconnect hardwired smoke detectors so that if one alarm is triggered all of the others go off simultaneously.1
The other common use for the red wire is switching. In a circuit where multiple switches turn a light on and off from different locations, the red wire provides for this option.
White Wires With Black or Red Tape: Hot
White wire insulation augmented with a red or black color marking usually indicates that it is being used as a hot wire rather than as a neutral wire. Typically, this is indicated with a band of black or red electrical tape wrapped around the wire’s insulation. Sometimes other colors are used, as well.1
For instance, a white wire in a two-wire cable may be used for the second hot wire on a 240-volt appliance or outlet circuit. This white wire should be looped several times around with black electrical tape to show that it is being used for something other than a neutral.
Bare Copper Wires: Ground
Bare copper is the most common type of wire color code to indicate a ground wire. Bare copper is the only wire color code that is not found on plastic wire insulation; it is simply the wire itself, devoid of insulation.1
All electrical devices must be grounded. In the event of a fault, grounding provides a safe route for electricity to travel to ground, instead using your body as the route.
Bare copper wires connect to electrical devices, such as switches, outlets, and fixtures, as well as metal appliance frames or housings. Metal electrical boxes also need ground connection because they are made of a conductive material. Plastic boxes are non-conductive and do not need to be grounded.
Green Wires: Ground
Green plastic insulation is sometimes used to indicate ground wires.1
Ground screws on electrical devices are often painted green, too. Never use a green wire for any purpose other than for grounding.
White or Gray Wires: Neutral
White or gray wire insulation indicates a neutral wire.1
When examining a white or gray wire, make certain that it has not been wrapped in electrical tape. This would indicate a hot wire.1 Older wires sometimes may lose their electrical tape wrapping. So, if the box has a loose loop of tape inside of it, there is the possibility that it may have come off of the neutral wire.
The term neutral can be dangerously deceiving as it appears to imply a non-electrified wire. It is important to note that neutral wires may also be carrying power and can shock you. While wires designated as hot (black or red insulated wires) carry power from the service panel (breaker box) to the device, neutral wires carry power back to the service panel. Thus, both hot and neutral wires have the potential to shock and injure you.
Blue and Yellow Wires
Blue and yellow wire insulation is sometimes used to indicate hot wires inside an electrical conduit.1
Rarely are blue and yellow wires found within NM cable sheathing. Blue wires are commonly used for travelers in three-way and four-way switch applications.
Benefits of Standard Wire Color Codes
Understanding and using standard wire color coding in electrical projects is important for safety, code requirements, and for more efficient organization of future electrical projects.
Using the wrong color codes will make you less safe because you are at a greater risk of shock. Your home is less safe, too, because improperly connected wires may cause a fire.
Being aware of electrical wire colors is valuable, too, since the electrical code requires that certain wires (neutral and ground) follow a standard color coding pattern.
Color-coded electrical wires help you with future projects and make them easier to accomplish since you don’t have to figure out the purpose of each wire. Each wire’s purpose is labeled for you.