Abstract: An industrial-rated molded case circuit breaker employs a pair of movable contact arms to interrupt circuit current through each phase of a multi-phase electrical power distribution circuit. A contact arm guide outboard the movable contact upon overcurrent conditions. A pair of protrusions formed on the abutting surfaces of the contact arms prevents the arms from distortion under the electrodynamic attraction generated during intense overcurrent conditions. A flexible arc gas exhaust-seal is arranged between the movable contacts and the line strap connectors to seal the circuit breaker enclosure while controllably exhausting the arc gases that occur upon such intense overcurrent conditions.