underground electrical box
The detailed analysis of **Underground Electrical Box** is as follows:
I. Definition and Function
The **Underground Electrical Box** is a waterproof and dustproof electrical enclosure specifically designed for underground
installation. It is used to protect devices such as **cable connections**, **switches**, and **wire splitters**, and is commonly
found in outdoor power, lighting, security, or irrigation systems.
II. Core Functions
1. **Waterproof and Moisture-proof**
- With a high protection rating (**IP67/IP68**), it can withstand immersion in groundwater and rainwater.
2. **Physical Protection**
- It is resistant to rolling and corrosion, protecting the internal devices from soil pressure and chemical erosion.
3. **Wire Splitting and Connection**
- It supports the installation of components such as cable connectors, terminal blocks, and small circuit breakers.
4. **Compliant Installation**
- It complies with outdoor electrical safety standards (such as NEC in the United States and GB 50169 in China).
III. Main Types
| Type Type | Material | Features | Applicable Scenarios |
| Embedded Junction Box | PVC/HDPE | Cylindrical or square, directly buried in the ground, with the top flush with the ground, and equipped with a waterproof sealing ring. | Streetlight and courtyard lighting wiring |
| Above-ground Outlet Box | Stainless Steel/Aluminum Casting | The box is above the ground, with a lockable cover, and supports the outlet of cables to devices (such as water pumps and charging piles). | Pool equipment, outdoor sockets |
| Wire Splitting Terminal Box | Plastic + Metal | It contains terminal blocks inside, used for splitting multiple circuits, small in size, and suitable for areas with a shallow burial depth. | Underground cable branching |
| Smart Control Box | Composite Material | Integrates controllers, sensors, and wireless modules, and supports remote monitoring (such as in irrigation systems). | Smart agriculture, smart home |
IV. Core Components
1. **Enclosure**
- Materials: **PVC** (corrosion-resistant, low cost), **304 Stainless Steel** (resistant to acids and alkalis, durable outdoors),
**Aluminum Casting** (lightweight and rust-resistant).
- Design: **Double-layer sealing cover**, **silicone sealing ring**, **drainage holes** (to prevent water accumulation).
2. **Internal Devices**
- Terminal blocks, waterproof connectors, small circuit breakers (below 16A), **GFCI (Ground Fault Circuit Interrupter)**
(necessary in wet environments).
3. **Installation Accessories**
- Cable gland (**Gland**), expansion bolts, grounding terminals.
V. Installation Key Points
1. **Location Selection**
- Avoid **waterlogging areas** and **areas prone to vehicle rolling**, with a burial depth of ≥ **30cm** (in the north, it should
be below the frozen soil layer).
- It should be at least ≥ **1.5 meters** away from buildings for easy maintenance.
2. **Foundation Construction**
- Lay a **10cm crushed stone cushion layer** at the bottom, and backfill with **fine sand** around the box (to reduce extrusion).
3. **Cable Connection**
- Use **waterproof cable connectors** (such as Perfit connectors) to ensure an insulation rating of ≥ **1kV**.
- Distinguish between **phase wires (L)**, **neutral wires (N)**, and **ground wires (PE)**, and the PE wire needs to be connected
to the grounding terminal of the box.
4. **Waterproof Test**
- After installation, inject clean water and observe for 24 hours without leakage.
VI. Purchase Guide
1. **Protection Rating**
- At least **IP67** (for short-term immersion), and for long-term underground installation, choose **IP68** (for continuous submersion).
2. **Load Capacity**
- For single-phase devices: 16A/250V; for three-phase devices: 63A/400V (a circuit breaker is required).
3. **Size Selection**
- Small size: 200×200×150mm (2-3 circuits); large size: 600×400×300mm (6-8 circuits).
4. **Certification Standards**
- In China: **CCC Certification**; in the European Union: **CE Certification (EN 62208)**; in the United States: **UL 50/50E**.
VII. Precautions
1. **Prohibited Behaviors**
- Do not directly bury it in **concrete** (maintenance space needs to be reserved);
- Do not install the box without grounding or use non-waterproof connectors.
2. **Maintenance Cycle**
- Check for **aging of seals** and **loosening of terminals** every year, and clean up any accumulated water in the box (if any).
3. **Cold Regions**
- Choose **cold-resistant materials** (no brittle fracture at -40℃) to avoid condensation and icing inside the box.
VIII. Product Examples
1. **ABB Underground Junction Box (IP68)**
- Made of PVC material, with a double sealing ring, suitable for the branching of streetlight cables.
2. **Honeywell Above-ground Outlet Box**
- Made of 304 stainless steel, with customizable socket modules, used for power supply to outdoor devices.
3. **Siemens Smart Irrigation Control Box**
- Integrates a PLC controller, with an IP67 protection level, and supports the access of soil moisture sensors.
IX. Relevant Specifications
- **China**: Code for Design of Low-Voltage Power Distribution GB 50054-2011 (outdoor underground part);
- **United States**: NEC Chapter 314 (box installation), Chapter 422 (outdoor devices);
- **International**: IEC 62133 (safety of outdoor enclosures containing alkaline batteries).
Conclusion
The key points of the underground electrical box lie in its **waterproof performance** and **structural strength**. When purchasing,
the material and protection rating should be selected according to the **burial depth**, **environmental humidity**, and **load
requirements**. During installation, strictly follow the **grounding** and **cable sealing** specifications to ensure long-term and
reliable operation.
