electric disconnect box
The following is a professional technical analysis of **"Electric Disconnect Box"**, in combination with electrical safety standards
and industrial application specifications:
I. Definition and Functions
The **Electric Disconnect Box** is a specialized electrical device used for **safely cutting off the power supply of an electrical
circuit**. Its core functions include:
1. **Power Isolation**: Achieve a **visible disconnection point** through a mechanical switch (NEC 110.22) to ensure there is
no voltage risk during maintenance.
2. **Overload/Short Circuit Protection**: Integrate **circuit breakers** or **fuses** to meet the requirements of **Overcurrent
Protection Device (OCPD)** (IEC 60947-2).
3. **Emergency Power Off**: Support **quick disconnection** (operating force ≤ 150N) to meet industrial safety standards
(NFPA 79).
II. Core Components and Technical Parameters
1. Typical Internal Components
| Component | Function | Standard Requirements |
| Isolating Switch | Provide a visible disconnection point, with a rated current of 16-630A (such as Siemens 3RV20) | Interrupting capacity ≥ 10kA (IEC 60947-3) |
| Circuit Breaker | Overload/short circuit protection (such as ABB T2S 160) | Tripping characteristics: Type B/C/D (GB 10963.1) |
| Fuse | High interrupting capacity fuse element (such as Bussmann NH00) | Interrupting capacity 100kA (UL 248-14) |
| Terminal Block | Copper bolt terminals, supporting wires of 6-35mm² (such as Panduit TB series) | Temperature rise ≤ 60K (IEC 60947-1) |
2. Electrical Parameters
- **Rated Voltage**: AC 230V/400V (single-phase/three-phase), DC 250V
- **Protection Level**: IP54 (indoor)/IP66 (outdoor) (EN 60529)
- **Operation Life**: ≥ 10,000 times (mechanical life)
III. Classification and Application Scenarios
1. Classification by Function
| Type | Features | Application Scenarios |
| Isolation Only Type | Without protection devices, pure mechanical disconnection (such as Eaton 99EB) | Bypass of solar inverters |
| Protective Type | Containing circuit breakers/fuses (such as Schneider NSX series) | Motor Control Center (MCC) |
| Emergency Stop Type | Red mushroom-shaped button, emergency stop response time ≤ 0.5s | Machine tools, production lines |
2. Classification by Installation Method
- **Wall-mounted Type**: Directly fixed to the wall (such as Rittal AE series)
- **Embedded Type**: Embedded in the wall, with a depth ≥ 150mm (such as Legrand Vario)
- **Floor-mounted Type**: Used outdoors, with a base (IP67, such as Hager OK 1200)
IV. Installation Specifications (Taking NEC/GB Standards as Examples)
1. Location Requirements
- **Accessibility**: 1.2-1.8 meters from the ground, with an operating space ≥ 0.9 meters (NEC 110.26);
- **Identification**: The box needs to be marked with **“DISCONNECT”** and circuit load information (GB 7251.3).
2. Wiring Requirements
- **Wire Colors**:
- Phase wires: L1 (yellow), L2 (green), L3 (red) (IEC 60446);
- Neutral wire: blue, PE wire: yellow-green double-color;
- **Wire Specifications**:
- For a 16A circuit breaker: ≥ 2.5mm² copper wire (GB 50217);
- For a 63A circuit breaker: ≥ 10mm² copper wire.
3. Grounding Requirements
- The metal box needs to be connected to the **PE busbar**, and the grounding resistance ≤ 4Ω (GB 50169);
- Use a **4mm² yellow-green double-color grounding wire** (multi-strand flexible wire).
V. Technical Key Points for Purchase
1. **Interrupting Rating**:
- It needs to be ≥ the line short-circuit current (such as 10kA@400V);
- Example: Select a high interrupting type of **100kA** for industrial scenarios (UL 489 certification).
2. **Environmental Grade**:
- In corrosive environments: Stainless steel material (316SS) + epoxy resin coating;
- In explosion-proof areas: Select products certified by **Ex d IIC T6** (IEC 60079-1).
3. **Interlocking Function**:
- Support **switch-door interlocking** (the door can only be opened after power is cut off);
- Support the **padlock function** (ISO 14119).
VI. Fault Diagnosis and Maintenance
| Fault Phenomenon | Possible Cause | Troubleshooting Method |
| The switch cannot be closed | Thermal-magnetic tripping due to overload | Reset the button + check the load current |
| Terminals are overheating | Loose or oxidized wires | Tighten with a torque wrench (8-10N·m) |
| The box is live | Grounding failure | Measure the resistance of the PE wire with a grounding resistance tester |
VII. Related Standards
- **International**: IEC 60947-3 (Low-voltage switchgear and controlgear);
- **United States**: NEC Article 404 (Switchgear);
- **China**: GB/T 14048.3 (Low-voltage switchgear and controlgear).
VIII. Comparison of Typical Products
| Brand | Model | Rated Current | Protection Level | Special Features |
| Siemens | 5SX6 160 | 160A | IP66 | With auxiliary contact feedback |
| Legrand | C200 | 200A | IP55 | Expandable modules (such as surge protection) |
| Delixi | DZ47S-63 | 63A | IP44 | Economical type, with CCC certification |
Conclusion
The core of the electric disconnect box is **safety isolation** and **overcurrent protection**. When purchasing, key attention
should be paid to the **interrupting rating**, **protection level**, and **environmental adaptability**. In the industrial field,
it is recommended to select models with **interlocking functions**, which comply with mechanical safety standards (ISO 13850).
