Variable impedance current limiting device

A variable impedance current limiting device, comprising:

• a housing defining a chamber therein;
• a pair of spaced electrical terminals respectively located at opposite ends of said housing and disposed in communication with said chamber;
• an electrically conductive fusible metal disposed in said chamber to provide an electrically conductive path between said terminals;
• an insulating member disposed in said chamber between the opposite ends of said housing defining a flow passageway that provides communication between said terminals across said chamber, said flow passageway including a constricted portion having a cross-sectional area and length substantially less than that of the rest of said flow passageway and said constricted portion extending through the center of said insulating member wherein with the occurrence of an overload current, vaporization of said fusible metal initially occurs in said constricted portion and is primarily contained in said flow passageway;
• and
• expansion means for buffering the pressure rise in said chamber when said fusible metal is vaporized.

A variable impedance current limiting device, comprising:

• a housing defining a chamber therein;
• a pair of spaced electrical terminals respectively located at opposite ends of said housing and disposed in communication with said chamber;
• an electrically conductive fusible metal disposed in said chamber to provide an electrically conductive path between said terminals;
• an insulating member disposed in said chamber between the opposite ends of said housing to define with an interior wall of said housing a flow passageway that provides communication between said terminals across said chamber, said flow passageway including a constricted portion having a cross-sectional area and length substantially less than that of the rest of said flow passageway wherein with the occurrence of an overload current, vaporization of said fusible metal initially occurs in said constricted portion and is primarily contained in said flow passageway;
• and
• expansion means for buffering the pressure rise in said chamber when said fusible metal is vaporized.

A variable impedance current limiting device, comprising:

• a housing defining a chamber therein;
• a pair of spaced terminals respectively located at opposite ends of said housing and disposed in communication with said chamber;
• an electrically conductive fusible metal disposed in said chamber to provide an electrically conductive path between said terminals;
• an insulating member disposed in said chamber between opposite ends of said housing and having an overall length less than said housing to define a flow passageway that provides communication between said terminals across said chamber, said flow passageway including a constricted portion extending through the center of said insulating member wherein the ratio of the cross-sectional area of said constricted portion to that of the rest of said flow passageway is between about 0.1 and 0.2 and the ratio of the length of said constructed portion to that of the rest of said flow passageway is between about 0.1 and 0.2;
• and
• means for buffering the pressure rise in said chamber when said fusible metal vaporizes.

A method of limiting current in a variable impedance current limiting device, said device including a housing defining a chamber therein, a pair of spaced terminals located at opposite ends of said housing and disposed in communication with said chamber, and an electrically conductive fusible metal disposed in said chamber to provide an electrically conductive path between said terminals, comprising:

• disposing an insulating member in said chamber between the opposite ends of said housing to define a flow passageway that provides communication between said terminals across said chamber;
• extending said flow passageway through the center of said insulating member with the diameter of said flow passageway being approximately equal to the length of said flow passageway wherein with the occurrence of an overload current, vaporization of said fusible metal initially occurs in said flow passageway;
• and
• buffering the pressure rise in said chamber when said fusible metal is vaporized.

A method of limiting current in a variable impedance current limiting device, said device including a housing defining a chamber therein, a pair of spaced terminals located at opposite ends of said housing and disposed in communication with said chamber, and an electrically conductive fusible metal disposed in said chamber to provide an electrically conductive path between said terminals, comprising:

• disposing an insulating member in said chamber between the opposite ends of said housing to define a flow passageway that provides communication between said terminals across said chamber;
• providing in said flow passageway a constricted portion that extends through the center of said insulating member wherein the cross-sectional area of said constricted portion is between one-tenth and one-fifth that of said flow passageway and the length of said constricted portion is between one-tenth and one-fifth that of said flow passageway;
• and
• buffering the pressure rise in said chamber when said fusible metal is vaporized.

A method of limiting current in a variable impedance current limiting device, said device including a housing defining a chamber therein, a pair of spaced terminals located at opposite ends of said housing and disposed in communication with said chamber, and an electrically conductive fusible metal disposed in said chamber to provide an electrically conductive path between said terminals, comprising:

• disposing an insulating member in said chamber between the opposite ends of said housing to define a flow passageway between the interior wall of said housing and said insulating member to provide communication between said terminals across said chamber;
• providing in said flow passageway a constricted portion wherein the ratio of the cross-sectional area of said constricted portion to that of the rest of said flow passageway is between about 0.02 and 0.05, and the ratio of the length of said constricted portion to that of the rest of said flow passageway is between about 0.02 and 0.05;
• and
• buffering the pressure rise in said chamber when said fusible metal is vaporized.