Components of the Incoming Line Cabinet

The incoming line cabinet is a core cabinet in the low-voltage power distribution cabinet that

 **receives external power sources and distributes electrical energy**. Its components can be 

classified into four categories according to their functions: **main circuit components**,

 **control and protection components**, **auxiliary components**, and **structural components**

. The following are the specific compositions and function descriptions:

### I. Main Circuit Components (Electrical Energy Input and Distribution)

#### 1. Power Inlet Terminals

- **Function**: Cable interfaces for connecting external power sources (such as the power grid, generators).

- **Types**: Copper nose terminals, bolt-type terminals, supporting the access of multi-core cables.

#### 2. Isolating Switch (QS)

- **Function**: **Disconnect the circuit without load**, providing obvious electrical isolation 

(such as ensuring safety during maintenance).

- **Features**:

  - Designed for large currents (such as 630A, 1000A), with a **visible break point** when opening the circuit;

  - Often connected in series with the circuit breaker and located upstream of the circuit breaker.

#### 3. Main Circuit Breaker (QF)

- **Function**: **Switch the circuit on and off with load**, and provide **overload and short-circuit protection**.

- **Types**:

  - Molded Case Circuit Breaker (MCCB, used for currents below 630A);

  - Air Circuit Breaker (ACB, used for currents above 630A, such as 1000A, 2500A).

#### 4. Current Transformer (CT)

- **Function**: **Measure the current of the main circuit** and provide signals for instruments and protection devices.

- **Configuration**:

  - Three CTs are configured for a three-phase incoming line cabinet (to measure three-phase currents);

  - The accuracy is Class 0.5 (used for ammeters) or Class 5P10 (used for protection).

#### 5. Busbar

- **Function**: **Distribute electrical energy** to each outgoing line circuit.

- **Specifications**:

  - Copper busbar (TMY) or aluminum busbar (LMY), and the cross-sectional area is selected

 according to the current (for example, a 100×10mm copper busbar is used for 1000A);

  - The surface is coated with plastic for insulation, and there are phase markings (L1 yellow,

 L2 green, L3 red).

### II. Control and Protection Components (Monitoring and Protection)

#### 1. Microcomputer Protection Device

- **Function**: **Intelligently monitor** parameters such as current, voltage, and leakage current, and 

** (coordinate with the circuit breaker to trip).

- **Functions**: Overload inverse-time protection, short-circuit instantaneous protection, zero-sequence

 leakage protection.

#### 2. Voltmeter/Ammeter

- **Function**: **Display the three-phase voltage and current values in real time**.

- **Configuration**:

  - Pointer instruments or digital displays, connected through CT/PT;

  - The voltmeter is equipped with a **changeover switch** (to switch the three-phase display).

#### 3. Surge Protector

- **Function**: **Protect against lightning strikes and surge voltages**, protecting equipment 

from overvoltage damage.

- **Type**: Metal Oxide Varistor (MOV) type, with a nominal discharge current of 10~40kA.

#### 4. Fuse (FU)

- **Function**: **Provide short-circuit protection for the secondary circuit** (such as the control 

circuit, instrument power supply).

- **Specifications**: Small fast-fusing fuses (such as 6A, 10A).

### III. Auxiliary Components (Operation and Indication)

#### 1. Control Button/Changeover Switch

- **Function**: Manually **close/open the circuit breaker** and switch the instrument display mode.

- **Types**: Red opening button, green closing button, with a mechanical anti-misoperation design.

#### 2. Indicator Lights

- **Function**: **Indicate the status**:

  - Power indicator light (green);

  - Circuit breaker closing indicator light (red);

  - Fault alarm light (yellow).

#### 3. Terminal Block

- **Function**: **Connect secondary control wires** (such as protection devices, instruments, external signals).

- **Specifications**: Rail-mounted terminal blocks, with clearly marked terminal numbers (such as 101, 102).

#### 4. Electric Energy Meter

- **Function**: **Measure the total electricity consumption**.

- **Type**: Single-phase or three-phase electronic energy meter, with an optional 485 communication interface.

### IV. Structural Components (Physical Support and Protection)

#### 1. Cabinet Frame

- **Material**: Cold-rolled steel plate (thickness 1.5~2.0mm), with a plastic-sprayed surface for anti-corrosion.

- **Protection Level**: IP30 (indoor) or IP54 (outdoor).

#### 2. Openable Cabinet Door

- **Design**:

  - The front door is installed with instruments and buttons, and is equipped with an **observation window**;

  - The back door or side door is used for wiring and maintenance.

#### 3. Wire Ducts and Cable Ties

- **Function**: **Organize the wire harnesses**, and separate the strong and weak current ducts

 (with a spacing of ≥100mm).

- **Material**: Plastic wire ducts, fixed with nylon cable ties.

### V. Schematic Diagram of the Typical Configuration of the Incoming Line Cabinet

### VI. Precautions

1. **Component Matching**: The rated current of the circuit breaker should be **≥** the current-carrying

 capacity of the incoming cable (for example, a 1000A cable is matched with a 1000A circuit breaker).

2. **Protection Coordination**: The protection setting value of the incoming line cabinet should be

 **greater than** that of the lower-level outgoing line cabinet to avoid( tripping).

3. **Grounding Design**: The cabinet body and the busbar should be connected to the grounding 

copper busbar through **grounding bolts** to ensure the reliable grounding of the PE wire.

Through the above components, the incoming line cabinet realizes the full-process functions of 

**power access → protection control → electrical energy distribution → status monitoring**, 

and it is the "entrance hub" of the low-voltage power distribution system.