Circuit breaker

A circuit breaker, comprising:

• a housing;
• a terminal disposed in said housing;
• a first movable arm disposed in said housing, including a first contact;
• a support member disposed in said housing;
• a second movable arm pivotally supported by said support member and being electrically connected to said terminal by a flexible lead, said second movable arm including a second contact and being disposed opposite said first movable arm so that said second contact contacts said first contact when a normal current flows, wherein said first movable arm exerts an electromagnetic repulsive force on said second arm in a direction where the first and second movable arm repel each other to open said first and second contacts in response to a current exceeding a predetermined value;
• an insulating member fitted with said support member and said terminal to form a unitary construction, said insulating member insulating said support member from said terminal;
• a rear cover disposed on said housing;
• a plate-like packing disposed between said housing and said rear cover;
• and
• a chamber disposed in said housing, said chamber including an opening, said plate-like packing including a plurality of windows in alignment with said opening, wherein said rear cover is held tightly against said housing so that said chamber is hermetically isolated by said plate-like packing disposed between said rear cover and said housing.