Cable trays without expansion joints

Cable trays do not always require expansion joints; they are only necessary for long runs or where significant thermal expansion and contraction may occur.

Thermal Expansion Considerations

Cable trays, particularly metallic ones, expand and contract with temperature changes.

According to NEMA V

E 1 standards, steel and aluminum cable trays have specific maximum lengths between expansion joints depending on the expected temperature differential. For example, a steel tray may require an expansion joint every 128 feet, while an aluminum tray may require one every 65 feet for a 100°F temperature change. Expansion joints are typically installed only where large temperature variations occur, such as rooftop installations.

Installation Practices

Proper installation allows cable trays to accommodate thermal movement without expansion joints in shorter runs. Supports should not clamp the tray so tightly that it cannot expand or contract. Instead, trays should be anchored at midpoint supports with hold-down clamps and guided at other supports to allow sliding movement.

Expansion joints are generally aligned with structural expansion joints rather than installed arbitrarily along the tray run, as the tray and supporting structure may have different thermal expansion rates.

Material and Design Factors

The need for expansion joints also depends on the tray material. Aluminum expands more than steel, so shorter intervals between joints are required for aluminum trays. Ladder-type cable trays without covers allow for better airflow and minimal heat buildup, reducing thermal stress and the need for frequent expansion joints.

Proper design, including support spacing and load considerations, can often eliminate the need for expansion joints in typical indoor installations.

Standards and Guidelines

While the NEC does not explicitly require expansion joints for cable trays, NEMA standards provide guidance on thermal expansion management. Manufacturers also offer expansion joint splice plates and bonding jumpers for grounding continuity when joints are used. Following these guidelines ensures safe, reliable, and long-lasting cable tray installations.

In summary, expansion joints are not universally required for cable trays. They are necessary only for long runs, extreme temperature variations, or specific structural conditions, and proper support and installation practices can often mitigate the need for them.