Permissible distance for electrical cables exiting the cable tray

Cables exiting a cable tray should not have an unsupported span exceeding 6 feet (approximately 1.8 meters) to prevent undue mechanical stress and ensure compliance with NEC and BS 7671 standards.

Key Guidelines

Unsupported Span: When cables leave a tray to connect to equipment, raceways, or junction boxes, the unsupported distance should generally not exceed 6 feet (1.8 meters). If the span is longer, additional supports such as cable clamps, brackets, or conduit must be installed to prevent mechanical strain on the conductors and terminations ( ). Support Intervals Within Trays: Horizontal cable trays typically require supports every 3 to 5 meters (10–16 feet) along straight runs, with closer spacing at bends, T-junctions, or heavy cable loads ( ). Vertical runs should have supports preferably less than 2 meters apart ( ). Mechanical Strain Considerations: According to BS 7671, cables must be supported to avoid undue mechanical stress, particularly at terminations. This includes accounting for the cable's own weight and any additional loads ( ). Bend Radius and Strain Relief: When exiting a tray, cables should maintain their minimum bend radius as specified by the manufacturer to prevent damage. Strain relief devices or clamps are recommended at the exit point to secure the cable and protect terminations ( ). Fire Safety: All supports used for cables, including those at tray exits, should be fire-resistant to prevent premature failure in case of fire ( ). Practical Tips:

• Secure cables at the start, end, and turns of the tray.
• Use listed cable ties or clamps suitable for the environment (UV-resistant for outdoor installations).
• Avoid overtightening ties to prevent jacket damage.
• For long outdoor runs, consider expansion splice plates to accommodate thermal expansion ( ). By following these guidelines, electrical installations maintain mechanical integrity, safety, and compliance with both NEC and BS 7671 standards.