Molded Case Circuit Breaker Exhaust Barrier

When industrial-rated circuit breakers are double-branch-connected within lighting panelboard assemblies, the line ends of opposing pairs of circuit breakers are arranged close together within the panelboard enclosure. For purposes of this disclosure, "double-branch" connection is defined as that arrangement whereby a pair of circuit breakers are connected to the same phase bus bars. The line terminal lugs are omitted and the circuit breaker line straps are connected with the bus bars by means of offset branch strap connectors.

The old style circuit breakers were open at the top of the line lug compartments to facilitate the insertion of a tool to connect the circuit breaker line terminal lugs within a multi-phase power distribution circuit. With newer designs, a cap is arranged over the line terminal compartments once the terminal connections were made to prevent inadvertent contact with the bus bars or line straps per se.

When an overcurrent condition occurs, the gases originating within one of the closely aligned circuit breakers could transfer to the other circuit breaker within the double-branch arrangement, resulting in a phase-to-phase fault.

To prevent the occurrence of such phase-to phase faults within prior art panelboards, a fiberboard barrier is inserted to prevent the exhaust gases from one of the circuit breakers from entering the line lug compartments of the opposing circuit breaker. Over long periods of continuous use, the fiber material could become brittle and deteriorate. Another problem with the fiberboard barriers suggested by the prior art, is the removal of the barrier for access to the line terminals and the subsequent connection of the circuit breakers to the line terminal straps without replacing the barrier.

One purpose of this invention is to provide an effective exhaust gas barrier that allows the circuit breakers to be connected to the line straps and removed from the line straps without first having to remove the exhaust gas barrier.

An exhaust gas barrier formed as a unitary plastic assembly includes means for direct attachment to terminal straps in the absence of line terminal lugs. The barrier also includes hinged extension baffles for insertion within the line strap compartments of adjacent electric circuit breakers connected in a double-branch arrangement within electric power panelboards. The baffle extensions are easily removed when the opposing circuit breakers include similar exhaust gas barriers.

FIG. 1 is a front view of an electric power distribution panel in accordance with the prior art;

FIG. 2 is a top perspective view of the exhaust gas barrier in accordance with the invention in isometric projection to a pair of opposedly faced circuit breakers;

FIG. 3 is an end view of the exhaust barrier depicted in FIG. 2;

FIGS. 4A, 4B are front views of the arc gas barrier depicted in FIG. 3;

FIG. 5 is a side view of a pair of similar circuit breakers connected in a double-branch configuration; and

FIG. 6 is a side view of a pair of dissimilar circuit breakers connected in a double-branch configuration.

An electrical distribution power panelboard 10 is shown in FIG. 1 and is similar to that described in the aforementioned U.S. patent application Ser. No. 388,452 and differs by bolt-on attachments between the circuit breakers 12A, 12B and the bus bars 15 containing the threaded openings 16. The circuit breakers and switches described in the aforementioned U.S. patent application are plugged onto the bus bars and the bus bars are accordingly arranged in the vertical rather than in the horizontal plane shown in FIG. 1. The panelboard includes a face plate 11 with a plurality of openings 14 arranged for accessing the circuit breaker handles 13.

The circuit breaker 12A is similar to the type described in U.S. Pat. No. 4,754,247, which Patent is incorporated herein for purposes of reference and which includes a plurality of line terminal screw caps 19 placed over the line terminal access openings 17, formed within the circuit breaker cover 22, which contain the line terminal screws 18.

The circuit breakers 12B shown in FIG. 2 are similar to those described in U.S. Pat. No. 4,757,294 and do not include terminal caps 19 as shown in the cover 22 of circuit breaker 12A over the respective line and load terminal screws. In order to prevent inter-phasal faults from occurring whereby arc gases emanating from either one of a pair of branch-connected circuit breakers 20 electrically contacts the line terminal screws in the opposing circuit breaker, the exhaust barrier 28 is employed. The exhaust barrier comprises three strap covers 29 having radial slots 32, which provide access to the line straps 24 and to the threaded openings 25 formed therein, while the opposing side walls 36, 37, top cover 33 and back wall 34 respectively block the egress of any exhaust gas from the openings 23 provided in the circuit breaker case 21. This is especially helpful when the circuit breaker line lugs, such as described within the aforementioned U.S. Pat. No. 4,754,247, are omitted and the straps 24 are connected to the bus bar by means of branch straps 42, as will be discussed below with reference to FIGS. 5 and 6. Still referring to FIG. 2, the exhaust barrier further includes three box-like extensions 30 attached to the strap covers 29 by means of a flexible hinge 31, integrally formed therein. The extensions are inserted within similar openings 23 formed in the case 26 of circuit breaker 12B to electrically insulate the line straps from any ionized exhaust gases. The horizontal slots 35, formed within the side walls provides clearance for the line straps. The web connector 38 that joins the three strap covers together provides for individual flexible movement of the strap covers to compensate for the differences in the spacing of the line straps as well as the size of the openings 23.

The function of the web connector 38 within the exhaust barrier 28 is best seen by referring now to FIG. 3. A line strap recess 27 integrally-formed within the strap cover 29 between the opposing side walls 36, 37 and the back wall 34. The top cover 33 closes the top portion of the recess, while the radial slot 32 provides access to the line terminal screws described earlier. The box-like extensions 30 extend from the back side of the top cover and are removable as will be discussed below in greater detail. The web connector 38 interfacing each of the individual strap covers 29 has a pair of elongated slots 39, 40 parallel to each other and running in opposite directions to provide three dimensional flexibility, as best seen by referring now to FIGS. 4A, 4B. Although three such strap covers 29 are employed for three phase applications, only two, namely 29A and 29B, are depicted herein for purposes of illustration. The two strap covers are interconnected by means of the web connector 38 that deforms to allow relative motion between the two strap covers. When the strap cover 29B in the exhaust barrier 28 is rotated in the indicated direction to accommodate a line strap that is at a slight angle to the horizontal plane, the elongated slot 39 expands at its open end 39A, while the elongated slot 40 contracts at its open end 40A, to thereby provide relative movement between the two strap covers without damaging the exhaust barrier. In FIG. 4B the strap cover 29A is rotated in the oppositely indicated direction, whereby the web connector 38 becomes deformed such that the elongated slot 39 contracts at its open end 39A while the elongated slot 40 expands at its open end 40A, allowing the adjacent strap cover 29B to remain in a fixed position.

When two similar circuit breakers 12A, 12A' are arranged in a double-branch application with bus bars 15 as depicted at 20 in FIG. 5, the box-like extensions 30 (FIG. 3) are removed from the exhaust barriers 28, 28' before insertion within the respective breakers. It is noted that the terminal screws 41 are electrically protected from any ionized exhaust gases emanating from either of the two circuit breakers. Double-branch-connection with the bus bars 15A, 15B, 15C is made by means of offset branch straps, as indicated generally at 42.

When connecting dissimilar circuit breakers 12A, 12B to form the double branch connection 20' in FIG. 6, the box-like extension 30 on the exhaust barrier 28 is inserted within the circuit breaker 12B and extends over and electrically insulates the line terminal screws 41. The line terminal screws are connected to the bus bars 15 by means of branch straps 42.