Abstract: A linear thermal expansion joint between two sections of power conductor rail formed of steel web and aluminum cladding about the web, each rail section longitudinally and vertically halved at the rail end through the center of the steel web creating a mating surface of selected expansion length. Each rail end includes an elongated slot and a guide block secured to the aluminum cladding and extending through the slot. The rail ends are slidingly secured together with bolts and spring washers on the guide blocks so that the rail ends overlap side by side with the mating surfaces facing each other sandwiching a brass slide plate which facilities longitudinal movement between the rail sections. Exposed ends of the rail contact surfaces are chamfered to eliminate snags or sharp surfaces and to compensate for small dimensional differences between rail sections during alignment and assembly of the expansion joint.