electrical pull box
The detailed analysis of **Electrical Pull Box (Electrical Pulling Box/Pulling Box)** is as follows:
I. Definition and Core Functions
The **Pulling Box** is a kind of box used in the **cable wiring system**, and its main functions are:
1. **Assisting Cable Laying**: When wiring over long distances or along complex paths, it provides a temporary operating space
to facilitate pulling the cable (reducing friction and damage).
2. **Transition Connection**: It serves as a transition point for the cable from one conduit to another.
3. **Inspection and Maintenance Entrance**: It allows for the inspection and replacement of cables at a later stage without the
need to damage the wall or floor.
II. Differences from Junction Box
| Type Type | Allowable Cable Joints | Main Purposes | Size | Installation Location |
| Pulling Box | Not Allowed | Cable pulling, turning, and threading | Larger (depth ≥ 15cm) | Straight section ≥ 30 meters or at bends |
| Junction Box | Allowed | Cable termination and branching | Smaller | Near fixed equipment |
III. Main Types and Application Scenarios
1. Classification by Installation Method
| Type Type | Features | Applicable Scenarios |
| Surface-mounted Pulling Box | Surface-mounted, with an openable cover for easy inspection | Industrial plants, below the ceiling |
2. Classification by Shape
- **Straight Type (Through Type)**: Used for threading cables in straight sections to reduce resistance.
- **Elbow Type (90°/45°)**: Changes the direction of the cable to avoid right-angle bends (the bending radius ≥ 6 times the outer diameter of the cable).
- **Three-way/Four-way Type**: Connects multiple conduits to form branch paths.
IV. Core Components and Materials
1. **Box Material**
- **Metal (Cold-rolled Steel/Stainless Steel)**: High strength, requires grounding, and is suitable for industrial environments.
- **Plastic (PVC/ABS)**: Corrosion-resistant and has good insulation properties, suitable for indoor or underground scenarios.
2. **Key Components**
- **Knockout**: A pre-opened hole design that is suitable for different sizes of conduits.
- **Grounding Terminal**: The metal box must be connected to the ground wire (PE).
- **Sealing Rubber Ring**: The underground type needs to be equipped with a waterproof rubber ring to prevent water vapor from entering.
V. Installation Specifications and Key Points
1. NEC (USA) and Chinese Standards
- **NEC 314.28**:
- A pulling box should be installed every **30 meters** in a straight section;
- The number of elbows ≤ **2** per 30 meters, otherwise the spacing needs to be shortened.
- **Chinese GB 50169-2016**:
- When the length of the cable passing through the pipe exceeds **30 meters without bends** or **20 meters with 1 bend**, a pulling box should be installed.
