How to distinguish the wire numbers on the distribution cabinet?

In the distribution cabinet, the distinction of wire numbers is mainly achieved through **numbering rules, marking positions, 

functional grouping**, etc., with the aim of facilitating installation, maintenance, and troubleshooting. The following are common

 distinguishing methods:

 I. Wire Numbers of the Main Circuit (Power Supply and Load Circuit)

The main circuit usually carries large currents and connects devices such as power supplies, circuit breakers, contactors, and motors. 

The wire number rules are as follows:

1. Three-phase Power Supply Identification

- **Three-phase Live Wires**: Represented by **L1, L2, L3** (or **U, V, W**), corresponding to the phase sequence of the three-phase 

power supply.

- **Neutral Wire**: Represented by **N**.

- **Ground Wire**: Represented by **PE** or a yellow-green double-color wire (the wire number may not be marked, but the color is

 fixed).

2. Motor Circuit Identification

- Three-phase Windings of the Motor: Represented by **U1, V1, W1** (the incoming terminal of the motor) and **U2, V2, W2** (the 

outgoing terminal of the motor).

- Example: The line from the contactor to the motor is marked as **U1, V1, W1**.

3. Characteristics of Wire Numbers in the Main Circuit

- Generally, it contains **letters + numbers**. The letters represent functions (for example, L represents the phase wire, and N represents

 the neutral wire), and the numbers represent the phase sequence or circuit number.

- The wire diameter is relatively thick, and the colors are mostly **red, blue, yellow-green**, etc.

II. Wire Numbers of the Control Circuit (Secondary Circuit)

The control circuit is used to control the on-off of the main circuit, and the wire number rules are more systematic, usually following the 

**GB/T 4026-2016** standard:

1. Digital Numbering Method

- **Single Circuit**: Starting from **1**, it increases in the direction of the current. For example:  

  `1 → Button → 2 → Contactor Coil → 3 → Thermal Relay → 0` (0 is the common terminal).

- **Multi-circuit Grouping**:  

  - For the same functional module (such as the contactor coil, button), use **continuous numbers**. For example:  

    The control circuit of contactor KM1: `101 → KM1 Coil → 102`;  

    The circuit of button SB1: `103 → SB1 → 104`.

2. Functional Grouping Identification

- **Power Supply Circuit**: The phase wires are marked as **1, 3, 5**, and the neutral wire is marked as **2, 4, 6**.

- **Contactor Coils**: Usually use **even numbers**, such as **102, 104**.

- **Buttons/Switches**: Use **odd numbers**, such as **101, 103**.

- **Sensors/Signals**: Use **X1, X2**, etc. (can be customized).

3. Characteristics of Wire Numbers in the Control Circuit

- Pure **digital numbering**, segmented according to the function of the circuit, which is convenient for reading the diagram.

- The wire diameter is relatively thin, and the colors are mostly **black, white**.

 III. Special Markings and Techniques

1. **Position of the Wire Number Sleeve**:  

Mark on the **insulation sleeves** at both ends of the cable to ensure that both ends are the same (for example, both ends of the 

cable are marked **101**).

2. **Comparison with the Circuit Diagram**:  

The wiring diagram of the distribution cabinet will clearly mark the corresponding relationship between the wire numbers and the 

components, and you can quickly locate them through the diagram.

3. **Functional Labels**:  

For complex circuits, **functional labels** can be attached, such as **"KM1 Coil", "SB1 Start"**.

IV. Example Explanation

- **Main Circuit**:  

Power Inlet → Circuit Breaker **QF** → Contactor **KM** → Motor **M**  

Wire Numbers: **L1, L2, L3** (Power Supply) → **U1, V1, W1** (Motor).

- **Control Circuit**:  

Start Button **SB1** → Contactor **KM** Coil → Thermal Relay **FR**  

Wire Numbers: **1 → SB1 → 2 → KM Coil → 3 → FR → 0**.

 V. Precautions

1. The wire numbers need to be **clear and wear-resistant** to avoid fading or falling off.

2. The **numbering rules** within the same distribution cabinet should be unified (such as all using numbers or letters 

+ numbers).

3. The neutral wire (N) and the ground wire (PE) need to be strictly distinguished and not confused.

Through the above methods, the wire numbers in the distribution cabinet can be quickly distinguished to ensure that the

 circuit connections are correct.