Comparative behaviour of silver tin oxide and silver cadmium oxide contact materials in commercially available contactors

An experimental study was undertaken to compare, under AC-4 electrical test conditions, the erosion pattern of silver tin oxide and silver cadmium oxide contact materials in commercially available low-voltage contactors. Test were initiated on commercially available block type contactors rated at 250 A, AC-4 fitted with silver cadmium oxide contacts and silver tin oxide contacts. In order to simulate real-life situations, no attempt was made to control the point of switching ON or OFF the contactors under test. It is observed that the contactors fitted with silver tin oxide tips showed higher erosion than the contactors fitted with cadmium oxide contacts. The same result was obtained when the test was repeated on a number of samples. The study concludes contrary to what has been reported by some others, that a contractor optimized for silver cadmium oxide would have higher erosion (under AC-4 conditions) if the contacts are replaced by silver tin oxide and vice versa