Overvoltage protection devices including wafer of varistor material

A method for providing an overvoltage protection, the method comprising:

• providing an overvoltage protection device including:
• first and second electrically conductive electrode members;
• a varistor member formed of a varistor material and electrically connected with each of the first and second electrode members;
• and
• an integral fail-safe mechanism operative to electrically short circuit the first and second electrode members about the varistor member by fusing the first and second metal surfaces in the overvoltage protection device to one another using an electric arc;
• and
• directing current between the first and second electrode members through the varistor member during an overvoltage event;
• wherein:
• the first and second metal surfaces are separated by a gap;
• the overvoltage protection device further includes an electrically insulating spacer member electrically isolating the first and second metal surfaces from one another;
• and
• the electric arc disintegrates the spacer member and extends across the gap to fuse the first and second metal surfaces.

An overvoltage protection device comprising:

• first and second electrically conductive electrode members;
• a varistor member formed of a varistor material and electrically connected with each of the first and second electrode members;
• an integral first fail-safe mechanism configured to electrically short circuit the first and second electrode members about the varistor member when triggered by a first set of operating conditions;
• and
• an integral second fail-safe mechanism configured to electrically short circuit the first and second electrode members about the varistor member when triggered by a second set of operating conditions different from the first set of operating conditions.

A method for providing an overvoltage protection, the method comprising:

• providing an overvoltage protection device including:
• first and second electrically conductive electrode members;
• a varistor member formed of a varistor material and electrically connected with each of the first and second electrode members;
• an integral first fail-safe mechanism configured to electrically short circuit the first and second electrode members about the varistor member when triggered by a first set of operating conditions;
• and
• an integral second fail-safe mechanism configured to electrically short circuit the first and second electrode members about the varistor member when triggered by a second set of operating conditions different from the first set of operating conditions;
• and
• directing current between the first and second electrode members through the varistor member during an overvoltage event.

An overvoltage protection device comprising:

• first and second electrically conductive electrode members;
• a varistor member formed of a varistor material and electrically connected with each of the first and second electrode members;
• and
• an integral fail-safe mechanism operative to electrically short circuit the first and second electrode members about the varistor member by fusing first and second metal surfaces in the overvoltage protection device to one another using an electric arc;
• wherein:
• the first and second metal surfaces are separated by a gap having a width in the range of from about 0.2 mm to 1 mm;
• and
• the electric arc extends across the gap to fuse the first and second metal surfaces.

An overvoltage protection device comprising:

• first and second electrically conductive electrode members;
• a varistor member formed of a varistor material and electrically connected with each of the first and second electrode members;
• and
• an integral fail-safe mechanism operative to electrically short circuit the first and second electrode members about the varistor member by fusing first and second metal surfaces in the overvoltage protection device to one another using an electric arc;
• wherein:
• the first metal surface is a surface of the first electrode member and the second metal surface is a surface of the second electrode member;
• the first electrode includes a housing having a metal housing sidewall and defining a housing chamber;
• the varistor member and at least a portion of the second electrode are disposed in the housing chamber;
• the first metal surface is a surface of the housing sidewall;
• the varistor member has first and second opposed, generally planar varistor contact surfaces;
• the housing includes an electrode wall having a first electrode contact surface engaging the first varistor contact surface;
• the second electrode includes a head positioned in the housing chamber, the head including a second electrode contact surface engaging the second varistor contact surface and a head peripheral surface surrounding the second electrode contact surface;
• the second metal surface is located on the head peripheral surface;
• and
• the overvoltage protection device includes a buffer chamber on a side of the head opposite the second electrode contact surface, wherein the buffer chamber is configured to limit propagation of electric arc away from the head.

An overvoltage protection device comprising:

• first and second electrically conductive electrode members;
• a varistor member formed of a varistor material and electrically connected with each of the first and second electrode members;
• and
• an integral first fail-safe mechanism operative to electrically short circuit the first and second electrode members about the varistor member by fusing first and second metal surfaces in the overvoltage protection device to one another using an electric arc;
• and
• an integral second fail-safe mechanism, the second fail-safe mechanism including an electrically conductive meltable member, wherein the meltable member is responsive to heat in the overvoltage protection device to melt and form a current flow path between the first and second electrode members through the meltable member.