Thermal limit curves for induction machines are defined. A procedure is established for the presentation of these curves, and guidance for the interpretation and use of these curves for machine thermal protection is provided.

2.1 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. 2.2 The guide also describes thermal limit curves for large squirrel-cage motors defined as those motor ratings built in frames larger than the frame normally used for 500 hp, 1800 r/min motors.

The purpose of this guide is to assist in a uniform understanding of the construction, interpretation, and use of motor thermal limit curves.