50 years of TMF contacts design considerations

The historical evolution of TMF or RMF contacts is discussed. Today the very basic guideline as prescribed by Harold. N. Schneider, 50 years ago, still prevails. This allows for simple, compact and robust contact designs. Better understanding of the thermodynamics of the arc has helped to design contacts coping with short circuit currents of up to 100 kA. Contact material improvement has helped to boost up the short circuit interruption performance, which today is equivalent to the AMF contact structures. Progress in the theoretical understanding of the arcing process, and the increasing base of experimental data permit to give guidelines to design a correct functioning TMF contact.