1993 NEC Section 300-7 (b) states that “Raceways shall be provided with expansion joints where necessary to compensate for the thermal expansion or contraction. A rung spacing of 6 to 9 inches (150 to 230 mm) is preferable when. Cable trays have no space to flex, and may bend or break bolts. In this guide, the expansion gaps are explained to be calculated, as well as how to select materials such as aluminum or steel. Continuous lengths >30 m shall incorporate expansion facilities. As cables and trays expand or contract, they can cause stress on the structure, leading to potential damage or misalignment.