The effect of organic atmosphere on durability of electric contacts

Switching experiments were carried out in a controlled atmosphere containing organic compounds such as aromatics, alcohols and carboxylic acids, and the effects of organic compounds on contact arcing characteristics were investigated. During switching in aromatic atmospheres, the gas between the contact surfaces became active, resulted in a rapid increase in arc energy. Carbonaceous deposits (black powder) were formed especially from aromatic compounds on electric contacts. The life of the relay, estimated from an induction period of rapid increase in arc energy, became longer under the atmosphere of alcohols and carboxylic acid. Especially, the life time under formic acid was three orders longer than that under toluene. It was found that the life time in the toluene/air mixed atmosphere can be prolonged over 100 times by the addition of formic acid. Arc energy of an activated relay could also be reduced to the initial level by adding formic acid. Organic compounds that have carboxyl groups were more effective to reduce arc energy under toluene/air atmospheres. Gas analysis with a mass spectrometer revealed that CO increased in the atmosphere after switching experiments. Therefore, it can be concluded that the organic deposits were oxidized by the action of carboxyl group under air.