Combination circuit breaker-lightning arrestor

A fail-safe lightning arrestor comprising, in combination:

• A. an automatic electric circuit breaker including
• (1) a line terminal for connection to an electrical service entry main,
• (2) a load terminal for connection to an external branch load circuit,
• (3) circuit interrupting contacts, and
• (4) a thermal-magnetic trip unit including
• a. a bimetal electrically connected in series circuit with said contacts between said line and load terminals, said bimetal mechanically operative upon being directly heated by current of overload proportions drawn by the external load circuit to initiate tripping of said contacts to their open circuit condition, and
• b. electromagnetic trip elements magnetically coupled with said series circuit and mechanically operative to initiate tripping of contacts to their open circuit condition in response to current of heavy overload and short circuit proportions drawn by the external load circuit;
• and
• B. a varistor having a first terminal connected to said series circuit at a point downstream from said contacts and said electromagnetic trip elements, said varistor being in thermally coupled relation with said bimetal.
• C. whereby, the heat generated by said varistor in response to low level abnormal current flowing therethrough under normal voltage conditions eventually precipitates trip initiating mechanical operation of said bimetal, while current of heavy overload and short circuit proportions drawn by said varistor under normal voltage conditions precipitates trip initiating mechanical operation of said electromagnetic trip elements.

Fail-safe lightning arrestor apparatus for installation in a circuit breaker panelboard fed from a single-phase, three-wire service entry having two mains and a neutral, the panelboard including a grounded bus to which the service entry neutral is connected, a pair of main bus bars to which the two service entry mains are individually connected, and a plurality of aligned male stabs alternately connected to the two main bus bars, each male stab being physically associated with a different breaker mounting position within the panelboard, said lightning arrestor apparatus comprising, in combination:

• A. a pair of combination circuit breaker-lightning arrestors, each including
• (1) a molded case compatible for mounting in a circuit breaker mounting position within a panelboard,
• (2) an automatic electric circuit breaker accommodated within said case, said circuit breaker including
• a. a line terminal in the form of an externally accessible female stab connector mounted by said case,
• b. an externally accessible load terminal mounted by said case,
• c. circuit interrupting contacts accommodated within said case, and
• d. a trip unit accommodated within said case and including a thermally actuated trip element connected in series circuit with said contacts between said line and load terminals, said trip unit being automatically operable to precipitate opening of said contacts to interrupt said series circuit, and
• (3) a voltage surge suppressor accommodated within said case in thermally coupled relation with said trip element and having
• a. a first terminal connected to said series circuit at a point beyond said contacts and said trip element from said line terminal,
• b. a second terminal, and
• c. a lead wire electrically connected at one end to said second terminal internally of said case and extending externally of said case through a portal therein to facilitate electrical connection of its other end to the grounded panelboard neutral bus;
• and
• B. means joining said cases of said combination circuit breaker-lightning arrestor pair in side-by-side relation;
• C. whereby said lightning arrestor apparatus is installable in adjacent circuit breaker mounting positions within the panelboard with the line terminal female stab connectors of said combination circuit breaker lightning arrestors plugged on the panelboard male stabs associated with the adjacent breaker mounting positions, said voltage surge suppressors being thereby individually connected in circuit across a different one of the service entry mains and the service entry neutral to shunt to ground the currents associated with lightning induced voltage surges appearing on either of the service entry mains, and the heat generated by either of said suppressors in response to abnormal current flowing therethrough under normal line voltage conditions is coupled to said trip element of the associated circuit breaker, ultimately leading to automatic operation of said trip unit to precipitate opening of said contacts of said associated circuit breaker.