Gotthard Tunnel
During 1909, the Gotthardbahn was integrated into the Swiss Federal Railways. On 18 October 1920, the first electric trains were run through the Gotthard Tunnel. Initially, the voltage had to be reduced from the desired to , because the grime deposited on the insulators by the steam locomotives encouraged excessive arcing. However, in May the next year, steam was replaced entirely by electric traction, and the problem of soot and grime was eliminated.