Introduction to Cable Bundling in Cable Trays

Bundling conductors in cable trays is permitted under NEC rules but requires careful attention to ampacity derating, heat dissipation, and tray fill limits.NEC Guidelines for BundlingThe National Electrical Code (NEC) Article 392.24(D) governs bundling of conductors in cable trays. Bundling is allowed, but the NEC requires that ampacity derating factors be applied when multiple conductors are grouped together, as heat buildup can reduce the current-carrying capacity of each conductor . The 2023 NEC updates clarify that smaller conductors, such as PV or DG cables, can be bundled, but the total number of conductors and the method of bundling must be considered to avoid overheating .Ampacity and Derating ConsiderationsWhen conductors are bundled:Heat dissipation is reduced, so the ampacity of each conductor must be derated according to NEC tables.Layering or tight bundling increases the derating factor, especially for long runs.Single-conductor cables and multiconductor cables have different fill and derating rules, and ladder trays provide better ventilation than solid-bottom trays, reducing the impact of bundling .Practical Installation TipsTray type matters: Ladder trays allow air circulation around cables, making bundling less restrictive, while solid-bottom or channel trays may require more conservative bundling .Rung spacing: Maintain proper spacing (typically 6–9 inches) to support cables and prevent sagging or excessive bending .Separation of power and signal cables: Bundling should not compromise separation requirements to avoid electromagnetic interference .Minimum bend radius: Ensure that bundled cables do not exceed their minimum bend radius at tray entries and exits .SummaryBundling in cable trays is a common and code-compliant practice when done correctly. Key considerations include:Applying ampacity derating for bundled conductors.Choosing the appropriate tray type for ventilation.Maintaining proper spacing and bend radius.Ensuring separation of power and signal cables. Following these guidelines ensures safe, efficient, and NEC-compliant cable tray installations while allowing for organized routing of multiple conductors .