What does the color of the wire insulation layer signify?

First, the circuit is divided into three types: the phase line (live wire L), the neutral line (zero wire N), and the protective ground wire (ground wire PE).

I.Single-phase 220V household/civil lighting and socket circuits (most commonly used)

1.Live wire (L):

Standard colors: yellow, green or red , choose one of the three.

Function: This live working line carries 220V voltage upon power connection; contact poses an electric shock risk.

Scenario:Main incoming line, switch inlet, right socket hole.

2.Neutral line (N)：

Standard color: Light blue (pastel blue)

Function:The circuit carries current during normal operation and does not exhibit any ground voltage under normal conditions.

Scenario: Left socket hole, lighting circuit wire.

3.Ground wire (PE, protective grounding):

Standard color: Yellow and green (alternating yellow and green)

Function:A safety protection conductor that conducts current during equipment leakage to prevent electric shock; no current flows under normal operating conditions.

Scenario:Connection of holes on a three-hole socket and wiring to the electrical appliance's metal casing.

Rigid requirement: This color is exclusively for ground wires and must never be used as live or neutral wires.

4.Supplementary information for old buildings:

In earlier years, there were no strict national standards for wiring systems. Black and white wires were commonly used as neutral wires, red wires as live wires, while yellow-green wires remained designated for ground conductors. For aging circuits, it is essential to use a voltage tester or multimeter to verify insulation status rather than relying solely on color identification.

II.Three-phase 380V industrial power circuit (for motors, air compressors, and high-power equipment)

Three-phase electricity consists of three phase conductors, one neutral conductor, and one ground conductor, and is primarily used for high-power loads in factories and commercial establishments.

1.Three-phase live wire：

L1: Yellow  

L2: Green   

L3: Red

The voltage between each pair of the three wires is 380V, while the voltage between a single wire and the neutral/ground wire is 220V.

2.Neutral wire (N): uniformly light blue.

3.Protective ground wire (PE): Uniformly colored in yellow and green (industry-wide standardized, the sole dedicated color).

III. DC Circuits (Charging Poles, Monitoring Systems, Low-Voltage Systems, Internal Equipment Wires)

It consists of a positive electrode, a negative electrode, and a ground connection, commonly used in low-voltage direct current (DC) applications.

1.DC positive (+): Brown

2.DC negative terminal (-): Blue (distinct from the light blue of AC; black is used in some scenarios)

3. DC grounding/protective wire: yellow-green dual-color

IV. Control/Signal Lines and Secondary Circuits (Switches, Relays, Access Control, Fire Protection, Lighting Control Lines)

Primarily used in low-voltage and control circuits, posing no risk of strong electrical currents; this is the industry-standard practice：

1.Black: Common control lines, shared circuit lines   

2.White: Light-control circuits, dual/multi-switch connection lines   

3.Orange, purple, gray: Primarily backup lines, signal control lines, and fire linkage lines   

4.White, gray: Also commonly used as low-voltage internal equipment connection lines

V. Key Contraindications & Practical Tips (Essential for Home Decoration/Construction)

1. Red and Bottom Lines: The yellow-green double-colored lines shall only serve as ground wires; their use as live wires or neutral wires is strictly prohibited, as such violations constitute a major safety hazard.

2. The color scheme for the same circuit segment must be consistent: For example, all live wires in a room should use red uniformly; avoid alternating between red and yellow sections.

3. Temporary wiring, power strips, and extension cords: Continue to follow the above rules; do not arbitrarily mix colors.

4. Overseas/Imported equipment: Color standards differ from national standards; never assume colors directly based on domestic specifications—electrical verification is mandatory.

The simplest memory mnemonic (for home use): Yellow, red, and green represent fire; light blue is the neutral line; yellow and green are specifically used for grounding.