Electricity: electrothermally or thermally actuated switches – Electrothermally actuated switches – Fusible element actuated
Patent
1977-05-05
1979-01-09
Broome, Harold
Electricity: electrothermally or thermally actuated switches
Electrothermally actuated switches
Fusible element actuated
337159, 337161, H01H 8506, H01H 8508
Patent
active
041340949
ABSTRACT:
A fusible element for a current limiting fuse includes two silver ribbons, each provided with a plurality of holes spaced apart along the length thereof which define fusible points of reduced cross sectional area, one of these ribbons including a conventional "M" spot consisting of a body of low melting temperature alloy such as tin-lead solder, in intimate contact with the silver ribbon. One end of each of the silver ribbons is joined to a respective end of a centrally disposed tin wire element by a copper interconnecting member. This tin wire central portion of the fusible element has a melt I.sup.2 t which is equal to or greater than that of the silver ribbons in series with it. The time-current characteristics of this fusible element at high magnitude fault currents and at low magnitude overload currents are determined respectively by the fusible points of reduced cross sectional area of the silver ribbons and by the "M" spot of one of the silver ribbons in the same way as in the fusible elements of known current limiting fuses. However, at intermediate fault currents, the tin element initiates melting of the fusible element much faster than a fusible element using only a perforated silver ribbon and a conventional "M" spot.
REFERENCES:
patent: 2816989 (1957-12-01), Sugden
patent: 3140371 (1964-07-01), Johann et al.
patent: 3571775 (1971-03-01), Kozacka
Broome Harold
Gealow Jon Carl
LaPorte Ronald J.
McDonald Thomas E.
McGraw-Edison Company
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