Large DC motors are used in various industrial applications. These motors repeatedly generate arcs between the brush and commutator, because the load change is intense and the current value is also large. In particular, for the case in which the current is concentrated on a part of the brush, brush burnout may occur as a result of overcurrent. Therefore, excellent brushes to withstand arc generation and with good electrical properties are required. In the present paper, we discuss the relation between contact voltage drop and frictional wear for electrical sliding contacts when high currents flow to the brush. Specifically, we investigate the means by which to prevent brush burnout when high-current flows to the brush. Copyright © 2010 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.