The Threshold Welding Current for Large Area Closed Contacts with Two or Three points of Contact

A model is developed to determine the peak current required to weld large area closed contacts with two or three points of contact. The model also predicts the threshold welding current for parallel contact structures used to carry large currents in high current switching devices. The model considers: (1) the total contact resistance of the closed contacts by including the expected constriction resistance as well as the resistance resulting from the high temperature of the contact spots; (2) the effect of the 'blow-off' force from the passage of the current through the contact spots; and (3) the reduction of the hardness of the contact metal in the vicinity of the high temperature at the contact spots. In general the model predicts the values found from experiment for large area contacts within the uncertainty of the material data given in the usual contact materials, data tables.