Abstract: The disclosure relates to an electrical circuit breaker comprising a housing having a pair of external terminals for connection to a source of electrical current. Current responsive means is supported internally of the housing and electrically connected to said terminals and to separable internal contacts. Current flow through said current responsive means effects separation of said contacts upon the occurrence of a predetermined electrical condition. A fusible element disposed externally of said housing is electrically connected in series with said contacts and current responsive means and is operable to effect interruption of the electrical circuit through said circuit breaker upon failure of said current responsive means to respond to said predetermined electrical condition.