Abstract: A non-arcing bias rail assembly for supplying an electrical bias potential to a moving workpiece/substrate holder, comprising an elongated metal strip adapted for mounting along a wall of a workpiece/substrate treatment apparatus and having a surface bounded by first and second opposed, laterally extending side edges; a bracket comprised of an electrically insulating material and including a first portion mounted on the surface adjacent to and extending along a portion of the first side edge, and a second portion forming an upstanding wall extending perpendicularly from the first portion and including a surface facing the second side edge of the metal strip; an electrically conductive bias contact spring assembly mounted on the upstanding wall of the bracket facing the second side edge; and electrically insulated wire means electrically connected to the bias contact spring assembly for supplying an electrical bias potential.