Thermal Expansion Coefficient of Copper

Copper tube in a hot-water riser expands about 17 mm per 100 m per 10 °C, and a domestic hot-water line going from 10 °C cold to 60 °C hot moves nearly 1 mm per metre. That is the ticking noise in a wall cavity: tube sliding through a tight hole or hanger. Plumbing codes therefore require oversized penetrations, sleeve or isolate the tube, and put offsets or expansion loops in long runs. Rigidly clamped copper eventually work-hardens and cracks at the restraint.

Copper's coefficient sits neatly between steel's and aluminium's, which matters at every dissimilar-metal joint — copper tube in a steel hanger, copper busbar bolted to aluminium lugs. The aluminium-to-copper connection is the classic failure: different expansion rates cycle the joint, the aluminium creeps, contact pressure falls, resistance rises, and the joint heats and eventually fails. Bimetallic lugs, anti-oxidant compound and Belleville washers exist to fight exactly this mechanism.