Switch with surge protection

Claim 2

A switch comprising: a sealed enclosure having a pair of conductive portions and an insulating member including an annular portion, said annular portion of said insulating member having a peripheral outer portion contacting one of said conductive portions and an inner peripheral portion contacting the other of said conductive portions, a pair of spaced electrodes each included within said enclosure and each connected to a respective one of said conductive portions, externally located portions of said conductive portions providing terminals for connecting said switch in circuit, the annular portion of said insulating member being constituted of a metal oxide varistor material.

Claim 3

The combination of claim 1 in which said metal oxide varistor material has an alpha in excess of 10 in the current density range of 10 3 to 102 amperes per square centimeter.

Claim 4

The combination of claim 1 in which the portions of said annular portion of said insulating member in contact with said conductive portions are spaced to provide a current flow between said conductor portions which is low when normal operating voltage appears across said conductive portions and when voltages in excess of normal voltage progressively appear thereacross a rapidly decreasing impedance is presented by said annular portion of said insulating member in accordance with the alpha of the material, thereby limiting the voltage appearing between said conductive portions.

Claim 5

The combination of claim 1 in which said outer and inner peripheral portions of said annular portion are cylindrical.

Claim 6

The combination of claim 1 in which said annular portion of said insulating member is provided with a side surface which is substantially planar, a conductive ring concentrically located on said side surface, said conductive ring being in conductive contact with one of said conductive portions, the edge of said conductive ring adjacent the other of said conductive portions being uniformly spaced with respect thereto in said side surface.

Claim 7

The combination of claim 1 in which said annular portion of said insulating member is provided with a side surface which is substantially planar, an outer conductive ring and an inner conductive ring concentrically located on said side surface, said outer conductive ring in conductive contact with said one conductive portion, said inner conductive ring in conductive contact with said other conductive portion, the adjacent edges of said ring being uniformly spaced in said side surface.

Claim 8

The combination of claim 1 in which said annular portion of said insulating member has a pair of major opposed faces, a layer of metal oxide varistor material bonded to one of said faces and outer peripheral portion of said layer conductively connected to said one conductive portion and an inner peripheral portion of said layer conductively connected to the other of said conductive portions, said layer being constituted of a metal oxide varistor material having an alpha in excess of 10 in the current density range of from 10 3 to 102 amperes per squAre centimeter, the spacing of said peripheral portions being set so that high impedance is presented between said peripheral portions when normal voltages appear between said peripheral portions and when voltages in excess of normal voltage progressively appear thereacross, a rapidly decreasing impedance is presented by said layer in accordance of the alpha of the material thereof, thereby limiting the variation in voltage between said conductive portions.

Claim 9

The combination of claim 1 in which said sealed enclosure includes a resilient portion for enabling said electrodes to be brought into contact with one another.

Claim 10

A switch comprising: a cylindrical metal shell having an open end and a closed end, a cover plate hermetically sealed to close said open end, said plate including an annular insulator having a terminal pin sealed to an inner peripheral portion thereof and a metal retaining ring sealed to the outer peripheral surface thereof, said retaining ring conductively sealed to said shell, an insulating liner in said shell having a transverse partition dividing said shell into two chambers, said chambers containing a quantity of mercury occupying less than half the volume thereof, said partition having an opening therethrough for the passage of mercury between said chambers, said partition having a well for mercury diametrically opposite said opening, said partition being constituted of a metal oxide varistor material having an alpha in excess of 10 in the current density range of from 10 3 to 102 amperes per square centimeter, the spacing of the bottom of said well in respect to the opposed surface of said partition being set so that a high impedance is presented therebetween when normal voltages appear between the pools of mercury in said chambers and when voltages in excess of normal voltage progressively appear thereacross, a rapidly decreasing impedance is presented by said partition in accordance with the alpha of the material of said partition, thereby limiting the variation in voltage between the the pools of mercury.

Claim 11

A switch comprising: a cylindrical metal shell having an open end and a closed end, a cover plate hermetically sealed to close said open end, said plate including an annular insulator having a terminal pin sealed to an inner peripheral portion thereof and a metal retaining ring sealed to the outer peripheral surface thereof, said retaining ring conductively sealed to said shell, an insulating liner in said shell having a transverse partition dividing said shell into two chambers, said chambers containing a quantity of mercury occupying less than half the volume thereof, said partition having an opening therethrough for the passage of mercury between said chambers, said partition having a well for mercury diametrically opposite said opening, said partition being constituted of a metal oxide varistor material having an alpha in excess of 10 in the current density range of from 10 3 to 102 amperes per square centimeter, the spacing of the bottom of said well in respect to the opposed surface of said partition being set so that a high impedance is presented therebetween when normal voltages appear between the pools of mercury in said chambers and when voltages in excess of normal voltage progressively appear thereacross, a rapidly decreasing impedance is presented by said partition in accordance with the alpha of the material of said partition, thereby limiting the variation in voltage between the the pools of mercury.