This guide defines thermal limit curves@ recommends a standard procedure for construction of the curves@ and provides the definitions and information necessary to properly use these curves. The guide also describes thermal limit curve* for large squirrel -cage motors defined as those motor ratings built in frames larger than the frame normally used for 500 hp@ 1800r/min motors. Purpose The purpose of this guide is to assist in a uniform understanding of the construction@ interpretation@ and use of motor thermal limit curves.