This paper presents theory of the Cold Load Harmonic, CLHARM. model algorithm for simulation of power feeder currents resulting from both Cold Load Pickup, CLPU, and the Step Voltage Test, STEPV. The STEPV method is also presented. Feeder parameters obtained from field STEPV measurement are used to predict CLPU on that feeder using the CLHARM algorithm. STEPV test measurements and actual measured CLPU currents on the same feeder are compared with computer predictions. The CLHARM aggregates feeder thermostatically controlled load to simulate regain of diversity during outage restoration. All feeder weather sensitive load is lumped in CLHARM, using mean parameter values of a simple thermodynamic model. The ultimate objective of this work is experimentally obtained feeder signatures for CLPU prediction as a feeder design tool.