Saturday: Why Aluminum-to-Copper Terminations Burn Down Panels
Why treating aluminum wire like copper wiring on terminals is a guaranteed recipe for arc flashes.
Aluminum is lighter and cheaper than copper, making it heavily preferred for large industrial feeder cables. However, the exact moment you land an oversized aluminum conductor onto a copper or brass terminal block, you start a ticking thermal time bomb.
Aluminum and copper have completely different coefficients of thermal expansion. Under heavy load, the termination naturally heats up. The aluminum expands more rapidly than the copper lug holding it, crushing itself into a slightly smaller shape (a process called “cold flow”). When the load drops and the joint cools, the aluminum shrinks—but it shrinks smaller than its original size.
Over hundreds of daily thermal cycles, this mechanical loosening gets progressively worse. A loose termination creates higher resistance. Higher resistance creates higher heat, which drives even more extreme expansion and contraction, creating a runaway thermal cascade that ends in a catastrophic panel fire or an explosive arc flash.
You cannot directly mate aluminum to copper. You must use explicitly rated AL/CU (Dual-Rated) mechanical lugs or bimetallic splicers, generously apply anti-oxidant joint compound, and torque the termination block to the precise inch-pounds specified by the manufacturer—never simply “Farmer Tight.”