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Necessity and Standards of Electrical Wiring Color Codes

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Posted on May 15, 2020
August 9, 2020
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Why Are Electrical Wiring Color Codes Important?

Electrical wiring color codes matter a lot even if there are safety features such as the fuse, the double insulation design and the earth wire in plugs and appliances for electrical connection.

For example, in a home electrical system, there are usually three wires/lines in a power cord or in the whole power link entering into buildings. One wire brings electricity to the appliance and one wire completes the circuit by taking electricity away from the appliance, these two wires are called “live” and “neutral/zero” respectively. The third wire is the earth wire designed for important safety considerations.

Imagining that a power link has been cut into two parts for an insertion of an additional appliance to support more electrical devices between the two parts. What would you do if there is no distinction of the three wires? If there is any mistake resulting in the misconnection of these wires, for example, the live wire is wrongly regarded as neutral wire or earth wire, big safety problems may occur. People dealing with the wires may get electrocuted or the circuit won’t work due to the wrong connection. Therefore, keeping the consistency of the wire colors before and after adding the appliances is vital. Given such potential hazards, electrical wiring color code standards is a necessity to be made. The electrical wiring color code standards not only help in appliance addition, but also offer support when there is a need to replace the old wires with new ones.

Electrical Wiring Color Code Standards

It is important to abide by the electrical wiring color code standards for safety concerns. Electrical wiring color code standards are specified according to different power distribution branch circuits: AC (alternating current) and DC (direct current).

AC is widely used in distribution and transmission electrical networks. In the low-voltage (the normal voltages of 240V and 415V delivered to most customers) distribution network, the transmission line generally adopts a three-phase four-wire system, of which three lines represent the three phases of L1, L2, and L3 respectively, and the other is a neutral line N. The neutral line in a three-phase four-wire system is different from the zero line or neutral line which enters the user's home in a single-phase transmission line. The zero line normally passes current to form a current loop in the single-phase line, while in a three-phase four-wire system, the three phases form a loop, and the neutral line is normally without current. In the 380V low-voltage distribution network, the N line is set to obtain the 220V line voltage from the 380V phase voltage, or for zero-sequence current detection in order to monitor the balance of three-phase power supply.

Example of Electrical Wiring Systems

Figure 1: Example of Electrical Wiring Systems

Note: Before the power supply enters the home, the PEN (Protective Earth and Neutral) will be grounded and then divided into PE (earth wire) and N. This grounding system is called TN-C-S by IEC 60364 or GB 16895.

DC distribution is limited to use in situations such as tramway and traction systems with a voltage of usually 600V, railway DC traction systems with a voltage of 1.5 kV between rail and overhead collector wire, lifts, printing presses and various machines where smooth speed control is desirable, electroplating or is simply used for battery charging. Usually, DC systems are of 2-wire or 3-wire types, of which a DC power has two terminals, one positive (+) and the other negative (-). The current flows from the positive terminal to the external circuit and returns to the negative terminal.

AC Power Circuit Wiring Color Code Standards

Different countries or regions have different AC power circuit wiring color code standards, of which the most important ones are illustrated below.

Most of Europe abides by IEC (International Electrotechnical Commission) wiring color codes for AC branch circuits. These are listed in the table below. One can replace or mix the wiring in some installations according to the color code change from the old IEC color to the new IEC color as shown in the following figure.

Function Label New IEC Color Old IEC Color
Protective earth PE green-yellow green-yellow
Neutral N blue blue
Line, single phase L brown brown or black
Line, 3-phase L1 brown brown or black
Line, 3-phase L2 brown brown or black
Line, 3-phase L3 grey brown or black

Mixed installation of old and new wire colours

Figure 2: Mixed installation of old and new wire colours

Note: Although the United Kingdom (UK) is no longer a member of the European Union (EU) since January 31st, 2020, the UK follows the IEC AC wiring color codes as well.

Different from the IEC AC power circuit wiring color codes, the US National Electrical Code (NEC) only mandates white (or grey) for the neutral power conductor, and bare copper, green, or green with yellow stripe for the protective ground.

Function Label Common Color Alternative Color
Protective ground PG bare, green, or green-yellow green
Neutral N white grey
Line, single phase L black or red (2nd hot)
Line, 3-phase L1 black brown
Line, 3-phase L2 red orange
Line, 3-phase L3 blue yellow

Governed by the Canadian Electric Code (CEC), the Canada AC power circuit wiring color codes shown below are similar to the US electrical wiring color code standards.

Function Label Common Color
Protective ground PG green or green-yellow
Neutral N white
Line, single phase L black or red (2nd hot)
Line, 3-phase L1 red
Line, 3-phase L2 black
Line, 3-phase L3 blue

DC Power Circuit Wiring Color Code Standards

DC power installations, for example, solar power and computer data centers, use color coding which follows the AC standards. The IEC color standard for DC power cable color code is listed in the table below.

Function Label Color
Protective earth PE green-yellow
2-Wire Unearthed DC Power System Positive L+ brown
Negative L- grey
2-Wire Earthed DC Power System Positive (of a negative earthed) circuit L+ brown
Negative (of a negative earthed) circuit M blue
Positive (of a positive earthed) circuit M blue
Negative (of a positive earthed) circuit L- grey
3-Wire Earthed DC Power System Positive L+ brown
Mid-wire M blue
Negative L- grey

Regardless of the IEC color standard, the US recommended DC power circuit wiring color codes as the following:

Function Label Color
Protective ground PG bare, green, or green-yellow
2-Wire Ungrounded DC Power System Positive L+ no recommendation (red)
Negative L- no recommendation (black)
2-Wire Grounded DC Power System Positive (of a negative grounded) circuit L+ red
Negative (of a negative grounded) circuit N white
Positive (of a positive grounded) circuit N white
Negative (of a positive grounded) circuit L- black
3-Wire Grounded DC Power System Positive L+ red
Mid-wire (center tap) N white
Negative L- black

In addition to the main electrical wiring color code standards mentioned above, there are other standards as well, such as the International/North American Conductor Color Coding. These standards have subtle differences with each other but mainly use green color and white color for earth wire and neutral wire coding respectively.

How to Check and Maintain the Safety of Electrical Wiring Circuit?

Except from the electrical wiring color codes, it is also important to check and maintain the whole electrical wiring circuit for safety concerns.

Check if there are abnormal smells or black burn marks around electrical devices. For example, check if there are black burn marks around wall power sockets or light switches. If there are, then the sockets or light switches may be worn out and may cause sparks when operated. Similarly, if there is any sign of smell like the smell of burning plastic or rubber, then the wire insulation may be breaking down causing short-circuiting or other problems. Under such circumstances, a double check of the wires behind the sockets and light switches is needed to make sure the wires are not deteriorating. If the wires are deteriorated, then one must replace the old ones as soon as possible.

Maintain a sound electrical wiring circuit. Do not give much burden to the existing circuit. Normally, there are not enough power points in a room installed in the past to satisfy the growing electrical needs today. Sometimes, appliances like a server, air conditioner, microwave oven, television, satellite video box, wireless access point and other charging devices may be inserted into one wall power socket through a power strip. These appliances will draw current and cause additional strain on the ancient insulation, which is easy to cause a household electrical fire. If necessary, choose power cables supporting high-power electronic equipment and add additional wall power sockets to support the devices you need or rewiring the house with a more suitable distribution of the power points.

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