The Molten Metal Bridge Stage of Opening Electrical Contacts

Measurements on the formation and rupture of the molten metal bridge have been made for a number of contact materials, for currents of 8A to 11KA and for contact opening accelerations of 0.4X 10³ms-2 to 16.0X 10³ms-2. The bridge has three regimes: The initial melting period, a stable period, and an unstable period during which it eventually ruptures. The bridge behavior during these three periods is explained in terms of the interaction between power input into the bridge, hydrodynamic and surface tension elfects, and magnetic pinclh effects. The shortest bridges occur at both the highest current [11KA) and at the lowest current (8A). The longest bridges occur for currents in the range 500A to 1000A. The bridges that show the longest unstable regime occur for opening acceh;rations between 0.5 X 103 ms-2 and 2.0X 10³ms-2