The authors of this article present an analytical method based on a Lumped Parameter Thermal Network (LPTN) in order to model the effect of an open phase fault on the thermal behavior of an induction motor under steady state and transient thermal analysis. The heat transfer generated by the conduction and convection in induction motor are discussed. The results obtained by the model developed are validated by experimental tests. The tested machine is a standard three-phase, 4-pole, 2.2 kW, 380 V squirrel cage induction motor of Totally Enclosed Fan Cooled “TEFC” design manufactured in Algeria by Electro-Industries.