DRAW-OUT CIRCUIT BREAKER UNIT WITH COORDINATED CABLE INTERLOCK AND SHUTTER
BACKGROUND OF THE INVENTION 5
1. Field of the Invention
This invention relates to circuit breakers, and in particular to draw-out circuit breakers mounted in an enclosure provided with a shutter to block access to the distribution 10 system conductors when the circuit breaker is removed from the enclosure. The invention further relates to an interlock for interlocking two such draw-out circuit breakers to prevent a condition in which both breakers are closed at the same time. 15
2. Background Information
Low voltage circuit breakers used in electric power distribution systems are commonly mounted in metal enclosures and supported on rollers which permits easy installation and removal of the sizeable circuit breakers required for such service. Typically, the line and load conductors are terminated in the rear wall of the enclosure with stabs which are engaged by finger connectors on the back of the circuit breaker as it is racked into the enclosure. In order to protect personnel from the exposed power system terminations 25 when the circuit breaker is removed, shutters have been developed which automatically close over the stabs as the circuit breaker is withdrawn, and which are opened by inward movement of the circuit breaker during installation.
In some applications, such as, for example, transfer switches which provide alternate power sources to a load, seeps must be taken to ensure that alternate sources with random phase relationship are not connected to the load at the same time. Interlocks have been developed which pre- 35 vent more than one switch from being closed at any given time. Often, circuit breakers are used as the switches which must be interlocked, and this includes the draw-out low voltage circuit breakers. One form of interlock for such circuit breakers is the cable interlock. Typically, this inter- 4Q lock includes a pivoted arm mounted behind the circuit breaker which pulls on a cable when rotated by a plunger which extends from the back of the circuit breaker when the contacts of that circuit breaker are closed. The cable actuates a device on the other circuit breaker which prevents the 45 contacts of that other circuit breaker from being closed. A similar cable interlock prevents the first circuit breaker from being closed when the other circuit breaker is. closed.
It is common for the cable interlock to hold the second circuit breaker in a tripped condition to prevent closure of 50 the contacts. When the first circuit breaker is removed from its enclosure, the interlock mechanism is exposed. Typically, in the case of a transfer switch under these conditions, the second circuit breaker would be closed to connect the alternate power source to the load. Usually, it is important in 55 such applications that power be maintained to the load. However, with the interlock exposed by removal of the first circuit breaker, it is possible that a worker could inadvertently or otherwise actuate the interlock device and trip the second circuit breaker, thereby, interrupting power flow to go the load.
Currently, there is no draw-out low voltage circuit breaker having both a shutter and an interlock, as these two mechanisms compete for space behind the circuit breaker. However, there is a need for a draw-out low voltage circuit 65 breaker which provides protection for personnel when the circuit breaker is removed and which when used with
another circuit breaker provides that both circuit breakers cannot be closed at the same time. There is a further need for such a circuit breaker unit in which the interlock cannot be actuated when the circuit breaker is removed from the enclosure to prevent an inadvertent or intentional tripping of the other circuit breaker to which the interlock is connected.
SUMMARY OF THE INVENTION
These needs and others are satisfied by the invention which is directed to a draw-out circuit breaker having an interlock which is blocked from preventing another circuit breaker to which the interlock is connected from being closed or maintained closed when the draw-out circuit breaker is removed from the enclosure. Furthermore, the invention is directed to such a draw-out circuit breaker having both an interlock and a shutter, and in fact, to a unique combination in which the shutter when closed upon removal of the circuit breaker prevents actuation of the interlock.
More particularly, the invention is directed to draw-out circuit breaker unit adapted for interlocking with another circuit breaker in an electrical distribution system having conductors with stabs on ends thereof, said unit comprising:
a circuit breaker having connectors projecting from a rear face thereof for connection to said stabs on said conductors of said electric power distribution system, separable contacts for interrupting current through said conductors, and a trip mechanism for tripping said separable contacts open in response to selected conditions of current in said conductors;
an enclosure having a rear wall in which said stabs on said conductors on said electric power distribution system are mounted, and means supporting said circuit breaker for movement toward said rear wall to an installed position in which said connectors engage said stabs to connect said circuit breaker in said electric power distribution system and movement away from said rear wall to disconnect said connectors from said stabs for removal of said circuit breaker from said enclosure;
interlock means comprising linking means linking said circuit breaker with said another circuit breaker, and actuating means associated with said circuit breaker for actuating said linking means to prevent closing of said another circuit breaker when said circuit breaker is in said installed position and said separable contacts of said circuit breaker are closed; and
prevent means preventing actuation of said link means when said circuit breaker is not in said installed position.
BRIEF DESCRIPTION OF THE DRAWINGS
A full understanding of the invention can be gained from the following description of the preferred embodiments when read in conjunction with the accompanying drawings in which:
FIG. 1 is a schematic view of a pair of circuit breakers interlocked by cable interlocks.
FIG. 2 is an isometric view with parts broken away of one of the interlocked circuit breakers of FIG. 1.
FIG. 3 is a horizontal sectional view through a circuit breaker incorporating a cable interlock and a shutter assembly in accordance with the invention and with the circuit breaker partially withdrawn from its enclosure and with the shutter assembly closed.