Arc extinguishing unit of molded case circuit breaker

An arc extinguishing unit of a molded case circuit breaker, comprising:

• fixed contacts fixed to part of a base assembly case;
• movable contacts that come in contact with or are separated from the fixed contacts;
• and
• an arc extinguishing part configured to extinguish an arc generated when the movable contacts are separated from the fixed contacts,
• wherein the arc extinguishing part includes:
• a pair of side plates disposed at both sides of the movable contacts and the fixed contacts;
• multiple grids installed at a fixed interval between the pair of side plates;
• and
• arc barriers each penetratingly-installed on the base assembly case in a slidable manner, and configured to be in an open state of being separated from the movable contacts when a normal current flows on a circuit or is cutoff, and to close between the movable contacts and the fixed contacts by being magnetized by a magnetic field generated by an arc between the movable contacts and the fixed contacts when a fault current is cut off.