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How does Discoloration of connection happen in contactor ?

Blackening of electrical connection occurs by sulfur or others. Sulfuration of connection

makes it from brown to black due to the thickness of the membrane of silver sulfide from

the gas in the air. The cause of sulfuration is hydrogen sulfide from foul water, polluted

river, human, exhaust gas, etc, which sulfurates alloyed silver. Silver sulfide is a

semiconductor membrane, which is not problem with usual situation or switching frequency,

however, it is the cause of bad contact with switching small current or low voltage. Sticking

a foreign substance causes the discoloration, black from carbon dissolved by arc, and

brown being scattered from oxide. Because silver oxide is not strong insulation membrane

like membrane of copper oxide, weak to heat, it can be pyrolyzed at 250℃ and destroyed

by low voltage, contact resistance is not matter in the circuit over 24V.

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