The contact resistance becoming larger generally will cause a large voltage drop on the contact, which will make the input power of the load equipment reduce. If one or two contact resistance become larger, will make the three-phase voltage of the load equipment unbalanced, which resulting in the phase-deficiency operation; and if the contact resistance is too large, will cause the electrical appliance itself overheating, and make its reliability reduced.
The reasons of the contact resistance becoming large:
1. The contact surface has dust, flower hair, grease and metal particles.
2. The soldering flux, rosin and others sundries were leaved in the electrical appliances while overhauling, and the escape of organic vapor in high temperature will contaminate the contact.
3. The contact surface is rusty or ablated by electric arc.
4. In humid environment, the water vapor in the contact surface may condense into frost at low temperatures.
5. Corrosive gases and vapors in the surrounding medium cause erosion to the contact and are coated with harmful insulating membranes on the contact surface.
6.The electrical wear and mechanical wear of contact.