electrical pull box underground
The following is a detailed analysis of the **Underground Electrical Pull Box**, covering its definition, functions,
types, applications, and key technical points: I. Core Definition The **Underground Electrical Pull Box** is a specialized enclosure used for **buried power/communication lines**,
mainly serving the following purposes: - **Wire Pulling Assistance**: Reduces the friction between the wires and the pipeline, facilitating the pulling of cables. - **Line Transition**: Provides a sealed space for cable joints to avoid direct burial in the ground. - **Maintenance Access**: Allows for later inspection, expansion, or troubleshooting. II. Core Functions
| Function | Technical Implementation |
| Waterproof Sealing | Adopts a protection rating of IP67/IP68, achieving moisture prevention through threaded compression, silicone sealing rings, and waterproof connectors (as in Abstracts 1 and 2). |
| Mechanical Protection | Made of concrete, hot-dip galvanized steel plate, or reinforced PVC material, which is resistant to crushing and corrosion (as in Abstracts 2 and 3) |
| Line Layout Flexibility | Supports Straight Pull or Angle Pull designs to adapt to different pipeline directions (as in Abstract 4). |
| Grounding Safety | The metal shell needs to be grounded, in compliance with the standards of NEC 250.118 or GB 50169 (as in Abstract 3). |
III. Main Types 1. Classification by Structure - **Straight Pull Box** - The inlet and outlet wire ports are **aligned in a straight line**, suitable for pulling cables over long distances
and reducing tension (as in Abstract 4). - **Angle Pull Box** - The inlet and outlet wire ports form an **angle of 90° or 45°**, used at the bends of pipelines to avoid excessive
bending of the cables (as in Abstract 4).
2. Classification by Material
| Material | Characteristics | Application Scenarios |
| PVC Plastic | Good insulation, light weight, low cost, but with weak compressive strength. | Home weak current systems, non-load-bearing buried lines. |
| Hot-dip Galvanized Steel Plate | High strength, fireproof, corrosion-resistant, and requires grounding protection. | Civil air defense projects, industrial projects (as in Abstracts 3 and 7). |
| Concrete | High compressive strength, resistant to aging, suitable for scenarios where heavy vehicles roll over. | Municipal power systems, buried under roads. |
IV. Typical Application Scenarios 1. **Buried Cable System** - Used for the intermediate transition of **long-distance cable threading**, avoiding abrasion of the cable sheath
during cable pulling (as in Abstract 2). 2. **Outdoor Lighting Project** - The branching points of streetlight and landscape light lines. Waterproof pull boxes can be directly buried in
the green belt (as in Abstract 1). 3. **Civil Air Defense Project** - The protective and airtight pull box needs to meet the **IP65 rating** and be made of 3mm thick hot-dip
galvanized steel plate (as in Abstracts 3 and 7).
4. **Water Supply and Drainage Monitoring**
- Cooperates with RTU equipment to protect the sensor lines in a humid environment (as in Abstract 1).
V. Key Technical Parameters
| Parameter | Common Specifications |
| Protection Rating | IP67 (protected against short-term immersion), IP68 (protected against long-term submersion). |
| Size | Small: 86mm×86mm (Type 86); Large: 180mm×150mm×120mm (for civil air defense type) to 48 inches×48 inches (for industrial type) (as in Abstracts 1, 3, and 6). |
| Rated Current | Usually does not directly carry current, depending on the specifications of the internal cables. |
| Installation Depth | The top is ≥300mm from the ground (on sidewalks) or ≥700mm (on driveways), specifically in accordance with the NEC 314.29 standard. |
VI. Installation Precautions 1. **Location Selection** - Avoid water accumulation areas and set it in the **straight pipeline section** or at a location where the **bend
radius is ≥6 times the pipeline diameter** (as in Abstract 5). 2. **Grounding Requirements** - The metal pull box needs to be connected to the ground wire through the **grounding screw**, and the non-metal
box body needs to ensure good grounding of the internal cables. 3. **Waterproof Testing** - Conduct an **air pressure or water pressure test** after installation (such as no leakage under a pressure of 0.4MPa
for 72 hours as in Abstract 1).
4. **Identification Management**
- Mark **"Power Pull Box"** on the ground to avoid damage during later construction (as in Abstract 6).
VII. Comparison: Pull Box vs. Junction Box vs. Through Box
| Type | Core Purpose | Is Wiring Allowed? | Common Scenarios |
| Pull Box | Assisting in wire pulling and reducing friction | Not allowed | Long-distance underground pipelines |
| Junction Box | Protecting cable joints | Allowed | Behind wall switches and sockets |
| Through Box | Transition when the line length exceeds the limit | Not allowed | Transition from exposed pipes to concealed pipes, from rigid to flexible. |
Conclusion The underground electrical pull box is a key component of the **buried line system**, with a focus on **waterproofness,
compressive strength, and access convenience**. When selecting, the model should be comprehensively determined according
to the environment (such as humidity, vehicle rolling), cable specifications (such as high-voltage cables vs. signal cables), and
industry standards (such as civil air defense, municipal), to ensure the long-term stable operation of the system.
