CIRCUIT BREAKER

PROBLEM TO BE SOLVED: To provide a circuit breaker with closing contacts stored in a relatively compact closing space, having a large rated current and good short circuit breaking performance. SOLUTION: The circuit breaker comprises the closing contacts 5, 11, 12 and the closing space formed by a base 1, a cover 2 and an upper cover 3 for storing the closing contacts. The closing space has a hole 3a at the upper part and a hole 30 at the lower part and also has a pressure sensing plate 32 rotatably provided at a position of hiding the hole 30 in a downward view, where a gap can be formed between an inside opening portion of the hole 30 and itself in a side view. In a steady state, room temperature outside air passes from the lower part of the closing space through the hole, the closing space and the hole 3a, in sequence, whereby temperature dissipation is caused in Joule heat generated in the closing contacts. When a large current is cut off, the pressure sensing plate 32 is rotated by the pressure of arc gas to block the hole 30, thus preventing the downward blow of the arc gas. COPYRIGHT: (C)2003,JPO