in ground electrical junction box
The following is a detailed description of the **In-Ground Electrical Junction Box**, covering its functions, types, installation
specifications, and precautions:
I. Core Functions and Purposes
The **in-ground junction box** is a sealed enclosure used to **protect the underground wire joints**, and its main functions are:
1. **Waterproof and Moisture-proof**: To prevent short circuits or electric leakage caused by the moisture in the soil.
2. **Mechanical Protection**: To prevent the cables from being crushed, punctured, or damaged by insects and rodents.
3. **Easy Maintenance**: It provides an inspection interface, allowing the lines to be checked without digging up the ground.
4. **Compliance**: It complies with electrical codes (such as Article 314 of the National Electrical Code (NEC) in the United States).
II. Main Types and Applicable Scenarios
1. Classification by Material
| Type | Material | Characteristics | Application Scenarios |
| Plastic Box | PVC, ABS | Corrosion-resistant, lightweight, low cost, and requires a waterproof sealing ring | Courtyard lighting, irrigation systems, low-voltage lines |
| Metal Box | Stainless steel, cast aluminum | High strength, resistant to crushing, and requires grounding to prevent electric shock | High-voltage lines, heavy-duty equipment |
2. Classification by Protection Level
- **IP67**: Dustproof + short-term immersion (water depth of 1m for 30 minutes).
- **IP68**: Dustproof + long-term submersion (water depth of over 2m).
3. Classification by Installation Method
- **Direct Burial**: The enclosure is directly buried in the soil and requires a **pre-embedded base** and a **waterproof cable joint**.
- **Shallow Burial**: Installed 10-30cm below the ground surface, with a **lifting ring** for easy opening.
- **Surface Mount**: Used above the ground and requires a **waterproof cover** and a **kick-proof baffle**.
III. Installation Specifications (Taking the NEC in the United States as an Example)
1. Location and Depth
- **Depth Requirements**:
- For low-voltage lines (≤30V): The burial depth ≥ **12 inches (30cm)**.
- For high-voltage lines (120V/240V): The burial depth ≥ **18 inches (45cm)** (NEC 300.5).
- **Keep Away from Obstacles**: At least ≥ **18 inches** away from the building foundation and at least ≥ **24 inches**
away from water pipes/gas pipelines.
2. Wiring and Sealing
- **Cable Joints**: Use **waterproof wiring terminals** (such as Liquidtight joints) and ensure they are wrapped with insulating tape.
- **Sealing Process**:
1. Fill the space between the enclosure and the cable with **silicone sealant** or **waterproof putty**.
2. The cover should be equipped with an **O-ring** and fixed with stainless steel screws.
3. Grounding Requirements
- The metal enclosure must be **grounded** and connected to the grounding rod through a 10AWG copper wire (NEC 250.118).
- If it is connected to the building grounding system, a **grounding jumper** should be used.
# IV. Installation Steps
1. **Trench Digging**: Dig a square pit according to the depth requirements and lay a 2-inch-thick gravel layer at the bottom for drainage.
2. **Fixing the Enclosure**:
- For direct burial: Fix the base with concrete to ensure the enclosure is level.
- For shallow burial: Install the lifting ring and cover it with an **anti-settlement cover plate**.
3. **Threading and Wiring**:
- After stripping the cable, connect it to the terminal and leave a slack of 6-8 inches.
- Wrap the joint with a **waterproof heat shrinkable tube**.
4. **Sealing Test**: Fill the box with 5cm of water and check for any leakage after 24 hours.
5. **Backfilling**: Compact the soil in layers and mark the location of the "electrical junction box" on the surface.
V. Safety Precautions
1. **Prevent Water Accumulation**:
- Reserve **drain holes** at the bottom of the enclosure or connect a drain pipe to the sewer.
- Avoid installing in low-lying and waterlogged areas.
2. **Prevent Corrosion**:
- Check the sealing ring of the plastic box every 5 years, and regularly apply anti-rust paint to the metal box.
3. **Voltage Matching**:
- Use **non-sealed boxes** (such as for landscape lights) for low voltage (12V/24V), and **fully sealed boxes**
must be used for high voltage.
4. **Clear Identification**:
- Set up **warning stakes** on the ground to indicate the purpose of the line and the voltage level.
VI. Common Problems and Solutions
| Problem | Cause | Solution |
| Water Accumulation in the Box | Seal failure or drain hole blockage | Replace the sealing ring and unclog the drain hole |
| Line Short Circuit | Joint water ingress or insulation damage | Remake the waterproof joint and test the insulation resistance |
| Enclosure Displacement | Loose backfilled soil or vehicle crushing | Reinforce with concrete and set up warning roadblocks |
| Metal Box Electrified | Grounding breakage or line leakage | Check the grounding system and test the leakage current |
VII. Recommended Products (U.S. Market)
1. **Plastic Direct Burial Junction Boxes**:
- **Raco 6810**: IP67, 10x10x6 inches, equipped with a waterproof sealing ring.
- **Carlon LB6**: Suitable for 1-2 cables, with a built-in bracket.
2. **Metal Sealed Junction Boxes**:
- **Hubbell HBL500**: Made of cast aluminum, IP68, supporting 4 cable inlets.
- **Crouse-Hinds EGS**: Explosion-proof design, suitable for hazardous environments.
3. **Low-Voltage Landscape Light Junction Boxes**:
- **Kichler 1205**: Dedicated to 12V, with a transparent cover for easy inspection and tool-free opening.
**Note**:
- It is **prohibited to install circuit breakers or switches** in the in-ground junction box (NEC 314.21),
and it is only used for joint protection.
- The installation of high-voltage lines must be carried out by a **licensed electrician** and a permit should be
applied for from the local municipal department.
- Regular inspection cycle: Open the cover for inspection every 2 years, and focus on checking the waterproof
performance before the rainy season. ⚡
