Low voltage vacuum switch with three internal contacts including a center floating contact

A direct current, low voltage vacuum switch which is operable to carry a high continuous current of several thousand amperes and to interrupt this arc current formed when the switch contacts are opened at a low dc voltage across the switch which extends the arc voltage above which the arc current would normally be sustained in vacuum between a single pair of spaced apart contacts, which switch comprises a hermetically sealed envelope having a central annular insulating portion, opposed thin flexible corrugated annular members extending inward from the central annular insulating portion in a direction transverse to the axis of the central annular insulating portion, movable high current carrying cylindrical conductive end contacts sealed to the inner annular edge of the thin flexible corrugated annular members, the improvement wherein a center contact is disposed within the hermetically sealed envelope between the opposed end contacts which are axially movable to and from contact with the center contact, which center contact is supported from the central annular insulating portion and electrically isolated from the opposed cylindrical end contacts in the open switch position where the end contacts are moved in opposed axial directions, and wherein the center contact is supported from the annular insulating portion by a central arc shield member disposed about the arc paths between the contacts and the annular insulating portion, with a thermally expansive support means connected between the annular insulating switch portion and the central arc shield member.