Contact make is usually not finished at the first touch, but as a consequence of bouncing the members make and break their contact several times before they reach a permanent state of contact. The bouncing of relay contacts brings many disturbances with it. The exactitude of contact make is lost, and the material transferred by arcs and bridges is increased, since each bounce means a new switching operation. A closing contact is particularly exposed to damage by rebounce when the current begins with a high inrush as is the case in a circuit containing wolfram filament lamps. The cold filament has a much smaller resistance than the glowing one, and the initial current may be 8 times the normal lamp current.
Unable to display preview. Download preview PDF.