Is it permissible to bundle cables inside cable trays

Cables inside cable trays should generally not be tightly bundled, except for specific cases like grouping multiconductor power cables to maintain voltage balance.

General Guidelines

Cable trays are designed to support and organize electrical cables without the need for tight bundling. Bundling all cables together can impede heat dissipation, potentially causing overheating and reducing cable lifespan, especially for power cables carrying significant current. Proper spacing within the tray allows air circulation, which is critical for maintaining ampacity and preventing insulation damage.

When Bundling Is Recommended

Bundling is sometimes necessary for multiconductor cables rated 600 volts or less to ensure balanced voltage distribution. In these cases, the bundle should include all three-phase conductors and the neutral if used. This practice helps prevent unbalanced voltages and ensures proper circuit performance.

Bundles should be secured with ties, but care must be taken not to compress the cables excessively, which could damage insulation or reduce airflow.

Best Practices

Segregate different types of cables: Power, control, instrumentation, and communication cables should be separated either by using separate trays or dividers within a tray to reduce electromagnetic interference and cross-talk. Maintain minimum bend radius: Avoid tight bends when routing cables in trays to prevent mechanical stress. Allow for future expansion: Over-bundling can make it difficult to add or remove cables later.

Use ladder or ventilated trays: These designs improve airflow and reduce the need for bundling while supporting cable organization.

Summary

While cable trays do not require all cables to be bundled, selective bundling of multiconductor power cables is acceptable and sometimes necessary for electrical performance. The key is to balance organization, heat dissipation, and accessibility while following NEC and industry best practices.