How to deduct the length of the cable tray

Cable tray length is generally not deducted; the full tray length is used for planning, but splice locations and support spans must be considered.

Key Considerations

Full tray length is used in calculations: Standard cable trays come in fixed lengths (e.g., 12, 20, 24, 30, or up to 40 feet) and are treated as whole units when planning installations . You do not typically deduct the tray length for overlaps or splices in the initial material calculation. Splice plates and support spans: When connecting two trays, a splice plate is used, and the tray must be at least as long as the support span. Only one splice plate is recommended per support span to maintain structural integrity . The distance between supports (span) affects tray strength and deflection, so planning must account for these spans rather than deducting tray length. Practical installation planning: While the tray length itself is not deducted, allowances for fittings, bends, and expansion joints should be included in the layout. This ensures proper alignment, load distribution, and compliance with NEC and NEMA standards . Summary: For material estimation and sizing, use the full tray length. Deduction is not required, but you must consider splice locations, support spans, and any additional fittings to ensure structural and electrical safety. This approach prevents underestimating the number of trays needed and avoids overcrowding or overloading the system .