Circuit breaker with metal melt isolation device

A circuit breaker comprising:

• a box-shape insulated container including a lower case having a lower wall and a lower side wall extending from the lower wall to define an open top surface at a side opposite to the lower wall, a middle case having a bottom wall disposed on the lower side wall of the lower case and a through hole formed in the bottom wall, and a cover disposed on the middle case,
• an opening and closing mechanism disposed on the bottom wall of the middle case,
• a holder situated adjacent to and actuated by the opening and closing mechanism, said holder being made of an insulating material and disposed in the through hole of the bottom wall of the middle case to be slidable perpendicularly to the bottom wall,
• movable and fixed contact shoes accommodated in the lower case, said movable contact shoe having a projection in a middle thereof to extend in a direction opposite to the lower wall and a concave portion formed inside the projection, said movable contact shoe being attached to the holder to provide an open and close operation relative to the fixed contact shoe when the holder is moved,
• a contact spring situated in the concave of the movable contact shoe to urge the movable contact shoe toward the fixed contact shoe, and
• an arc-extinguishing chamber accommodated in the lower case and surrounding the movable contact shoe.