1 : A method for determining a minimum cooling down time for current limiting devices in a step start process, comprising: measuring a rate of cooling of said current limiting devices; connecting power to a load through said current limiting devices for a step start interval of time; measuring current signals representing current flowing through said current limiting devices; sampling said current signals during sampling time intervals to obtain step start current sample values; squaring said step start current sample values to give heat values related to heat dissipated during each said sampling time interval; summing said heat values for all said sampling time intervals during said step start interval to give a total heat value related to total heat energy dissipated by said current limiting devices during said step start interval; and determining said minimum cooling down time for said current limiting devices, dependent upon said total heat value and said rate of cooling.