How many meters of horizontal cable tray require expansion joints

Expansion joints are required in horizontal cable trays when thermal expansion or contraction exceeds the allowable length between joints, typically every 39–39 meters for steel and 20 meters for aluminum under a 100°F temperature differential.General GuidelinesCable trays expand and contract with temperature changes, and expansion joints are installed to prevent structural stress, misalignment, or damage to the tray and cables (NEC Section 300-7(b), NEMA VE 1) . The spacing of expansion joints depends on:Material of the tray: Steel expands less than aluminum, so it requires fewer joints.Temperature differential: Greater temperature swings require closer spacing.Installation environment: Outdoor or rooftop installations with large seasonal temperature variations need more frequent joints.Typical SpacingAccording to NEMA VE 1 standards:Steel cable trays: Require an expansion joint approximately every 128 feet (39 meters) for a 100°F (≈56°C) temperature differential .Aluminum cable trays: Require an expansion joint approximately every 65 feet (20 meters) for the same temperature differential . These values are based on the maximum expected temperature change from winter to summer. The actual gap at the expansion joint is calculated using a nomograph or formula considering the installation temperature and expected temperature extremes .Installation ConsiderationsSupports: Place a support within 2 feet (≈0.6 meters) of each side of the expansion joint splice plate.Anchoring: Anchor the tray at the midpoint between expansion joints and use expansion guides at other supports to allow sliding during thermal movement .Splice plates: Use slotted or expansion splice plates to allow movement; standard rigid plates can prevent expansion and cause bending or bolt elongation .SummaryThe number of meters of horizontal cable tray before an expansion joint is required depends on the tray material and temperature differential:Steel: ~39 meters per joint for 100°F differentialAluminum: ~20 meters per joint for 100°F differential Adjustments should be made for local temperature extremes, installation conditions, and specific manufacturer recommendations to ensure safe and reliable operation of the cable tray system .