Tin plating investigation as a potential alternate to silver plating in plug in connection for low voltage low amp miniature circuit breakers

This paper reports the investigation of tin plating as a potential alternate to silver plating on plug in line terminal connections for low voltage low amp miniature circuit breakers. The plug in line terminals are typically connected on the enclosure interior bus bars and clamped with a spring clip. The substrate material of the line terminal was a copper alloy. The line terminals with both, tin and silver plating, were investigated on tin plated aluminum and bare copper bus bars. The connections were examined by cycling 50 Amps ac, one hour on and one hour off for 2,100 cycles in an ambient temperature of 25°C. The examined parameters were bulk temperature and voltage drop. SEM observations have been made for both, tin and silver plating, after the current cycling. Additionally, the plating deterioration on the contact spots was measured for oxygen and copper contents by EDX analysis. The analysis results indicated much higher contents of oxygen and copper on the tin plated connectors than the silver plated connectors which is consistent with the connector plating deterioration and fretting that was observed with the SEM.