The XRB class were built by Pacific National at their South Dynon workshops. They are mechanically similar to XR class locomotives, but are B units without driving cabs. XRB locomotives are designed to be used as booster units on standard gauge interstate freight trains, and must be led by a locomotive with a conventional driving cab. The units do not have hostler controls for moving them around yards and depots, only being fitted with a dead engine device and park-brake button. All three class members are currently stored at the Port Augusta Workshops.