SKF has developed a range of motor shaft earthing kits to help prevent bearing failures caused by the electrical discharge currents that can occur when variable-speed drives are used to control AC motors. The maintenance-free TKGR kits are claimed to improve system reliability, helping to avoid motor repairs and unplanned downtime, thus offering a high potential return-on-investment.

The kits consist of: a shaft earthing ring (shown above) with conductive brushes that are held against the surface of the motor shaft by an aluminium brush holder; four sets of mounting brackets allowing the ring to be fitted to almost any IEC frame motor up to 75kW; and a selection of mounting screws, washer and Allen keys.

There are nine sizes of ring to suit IEC frame motors with shaft diameters from 28–95mm. Depending on the motor power and application, the kit may need to be used in combination with SKF’s Insocoat or hybrid bearings.

The kits, which are designed to be retrofitted to existing IEC frame industrial motors, help to prevent damage caused by electrical discharge currents in rolling bearings. They can protect the bearings in attached equipment as well as those in the motor.