Electricity: electrothermally or thermally actuated switches – Electrothermally actuated switches – With longitudinally expansible solid element
Patent
1991-04-19
1992-04-14
Broome, Harold
Electricity: electrothermally or thermally actuated switches
Electrothermally actuated switches
With longitudinally expansible solid element
337395, 361103, H01H 6106, H01H 7118
Patent
active
051051788
ABSTRACT:
An over-current/over-temperature protection device which includes first and second electrical contacts, a separable resistance electrical separable path extending between the contacts, a breaker means and a heater. The heater comprises the separable path. The breaker breaks an electrical connection between at least one of the contacts and the separable path when current above a threshold value passes through the separable path and/or the over-current/over-temperature protection device reaches a threshold temperature. The breaker includes a member of a shape memory alloy which changes shape from a first configuration to a second configuration when the member is heated from a first temperature T.sub.1 to a second temperature T.sub.2. The heater heats the member from the first temperature T.sub.1 to the second temperature T.sub.2 so that the member changes from the first configuration to the second configuration. The over-current/over-temperature protection device can include a spring for changing the member into the first configuration when the member cools from the second temperature T.sub.2 to a temperature T.sub.3 below T.sub.2. The over-current/over-temperature protection device can include a permanent resistance electrical current path having a resistance higher than the separable path. The permanent path minimizes arcing when the electrical connection between the separable path and at least one of the contacts is broken by the breaker.
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