The present invention relates to a circuit breaker for lines, which includes a monopolar switching unit installed in an external box of the circuit breaker. The monopolar switching unit includes: a fixed contact which contacts or is separated from the inside of a base, which is an external case of the monopolar switching unit; a driving contact; a perturbation part which supports the driving contact to have the moving contact rotate, and a detection device part which detects an abnormal current. A heat radiation part which emits heat from the base to the outside of the base is provided on a lateral side of at least one among the contact part which the moving contact contacts, the perturbation part, and the detection device part. Thus, an increase in the temperature of a circuit breaker for lines can be prevented without an increase of costs in a limited space.;COPYRIGHT KIPO 2016
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