Junction Box and Clamp Dimensions
The clamp size included with a junction box depends on the cable cross-section and the box model, typically ranging from M16 to M63 metric knockouts for standard copper or aluminum conductors.
Clamp Function and Purpose
A junction box clamp, also called a cable connector or strain relief fitting, secures the cable where it enters the box, preventing it from shifting or being pulled out. It protects the internal conductors from tension, abrasion, and loosening, ensuring a safe and reliable electrical connection .
Standard Clamp Sizes
Clamps are selected based on the outer diameter of the cable and the junction box knockout size. Common metric sizes for Hensel junction boxes include:
- M16 / M20: For small cables, typically 0.14–4 mm² cross-section .
- M20 / M25 / M32: For medium cables, 1.5–16 mm² cross-section .
- M25 / M32 / M40: For larger cables, 10–35 mm² cross-section .
- M25 / M40 / M50 / M63: For very large cables, 16–70 mm² cross-section . The exact clamp size depends on the number of conductors and their cross-section. For example, a DK 0402 G box accommodates 0.75–4 mm² conductors with M20 knockouts, while a DK 1616 G box supports 10–25 mm² conductors with M25/M32/M40 knockouts .
Selection Tips
- Measure the outer diameter of the cable, including insulation, not just the conductor.
- Match the clamp to the junction box knockout size.
- Ensure the clamp type (plastic, metal, or snap-in) is suitable for the installation environment and cable type .
- For multiple cables, select a clamp that can accommodate the largest cable bundle. Using the correct clamp ensures compliance with electrical safety standards, prevents cable damage, and maintains a secure connection inside the junction box .
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