General Some new drive installations can have their bearings fail only a few months after startup. Failure can be caused by high frequency currents， which flow through the motor bearings. While bearing currents have been around since the advent of electric motors， the incidence of damage they cause has increased during the last few years. This is because modern variable speed drives with their fast rising voltage pulses and high switching frequencies can cause current pulses through the bearings whose repeated discharging can gradually erode the bearing races. Avoiding bearing currents To avoid damage occurring， it is essential to provide proper earthing paths and allow stray currents to return to the inverter frame without passing through the bearings. The magnitude of the currents can be reduced by using symmetrical motor cables or inverter output filtering. Proper insulation of the motor bearing construction breaks the bearing current paths.