How to Distinguish between an Air Switch and an Isolating Switch

In the power distribution cabinet or circuit system, the **air switch (circuit breaker)** and the 

**isolating switch** are two devices with different functions, which can be quickly distinguished through

 the following aspects:

### I. Differences in Core Functions

### II. Differences in Appearance and Structure

#### 1. Air Switch (Circuit Breaker)

- **Appearance Features**:

  - Usually has a **plastic casing**, with a relatively small volume, and there is a **closing/opening operation

 handle** (blue or black) at the top;

  - The panel is marked with the **rated current** (such as C32, D63), **number of poles** (1P, 2P, 3P) and the 

**residual current protection mark** (if any);

  - Some are equipped with a **test button** (T button) and a **reset button** (R button, which pops up 

in case of leakage).

   (Schematic diagram)

- **Internal Structure**:

  It contains a **bimetallic thermal release mechanism** (for overload protection) and an **electromagnetic

 release mechanism** (for short-circuit protection), and can trip automatically.

##YouTube：https://youtube.com/shorts/VE0l3tf9oY4

## 2. Isolating Switch

- **Appearance Features**:

  - Mostly has **exposed metal blades** or a **transparent casing**, the operation handle is **lever-type or 

rotary-type**, and a **clear disconnection gap** can be seen when the switch is open;

  - The marking is simple, only indicating the **rated voltage/current** (such as 100A 400V), without 

protection parameters;

  - High-current isolating switches are often equipped with an **arc extinguisher** (but it cannot extinguish 

the load arc).

   (Schematic diagram)

- **Internal Structure**:

  It only has **mechanical contacts**, without a protection device, and the circuit is disconnected by manual

 operation.

### III. Operation Modes and Scenarios

#### 1. Air Switch

- **Operation Scenarios**:

  - Used for **direct control of the load circuit** (such as household sockets, motor circuits);

  - Can be operated with load frequently, and the power supply can be restored by resetting after tripping.

- **Typical Applications**:

  The **main switch** and **branch switch** in the household distribution box, and the **incoming power

 protection** of industrial equipment.

#### 2. Isolating Switch

- **Operation Scenarios**:

  - Only operated when there is **no load or low load** (the upstream circuit breaker needs to be

 disconnected first);

  - Used for **safety isolation during electrical maintenance** to ensure that the circuit is completely

 powered off.

- **Typical Applications**:

  The **inlet end** of the power distribution cabinet (connected in series with the circuit breaker), 

**dual-power switching system**, and **isolation of capacitor banks**.

### IV. Position Relationship in the Circuit

- **Correct Wiring Sequence**:

  **Power Supply → Isolating Switch → Air Switch → Load**

  ▶ The isolating switch must be **connected in series upstream of the air switch** to ensure that the 

air switch has disconnected the load first when the switch is open.

### V. Safety Precautions

1. **Risk of Misoperation**:

   - It is strictly prohibited to use the isolating switch to cut off the **fault current** or **normal operating 

current**, which may cause arc burns or equipment damage;

   - After the air switch trips, the fault needs to be checked first and then reset to avoid repeated tripping

 that may lead to a fire.

2. **Marking Identification**:

   - The air switch is marked with **"Circuit Breaker", "MCB" or "QF"**;

   - The isolating switch is marked with **"Isolating Switch", "QS" or "DS"**.

### VI. Summary: Quick Distinguishing Mnemonic

- **Look at the Protection**: The one with overload/short-circuit protection is the air switch, and the one 

without protection is the isolating switch;

- **Look at the Contacts**: The one with a clear disconnection point after opening is the isolating switch,

 and the one with a fully enclosed casing is the air switch;

- **Look at the Marking**: The one marked with "QF" or with the rated current having "C/D" is the air switch, 

and the one marked with "QS" is the isolating switch.

Through the above methods, the two can be accurately distinguished in the power distribution cabinet or

 circuit to ensure safe operation.