Because of their simple structure and low-maintenance characteristics, railways in Japan have often adopted overhead rigid conductor lines for current collection systems applicable to underground track sections or tunnels. With regard to the copper Type T rigid conductor line adopted on some JR commercial lines, undulating wear appeared at intervals of about 60 mm on contact wire sliding surfaces. Such wear would cause impaired train speedup and thus increase maintenance costs. We investigated the causes of the wears, and proposed measures to improve the quality of overhead rigid conductor lines.