US3288956A

US3288956A - Draw-out switch-gear interlock apparatus

Info

Publication number: US3288956A
Application number: US435885A
Authority: US
Inventors: Charles L Jencks; Frank H Murphy
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1965-03-01
Filing date: 1965-03-01
Publication date: 1966-11-29
Anticipated expiration: 1983-11-29
Also published as: GB1126862A; DE1640134A1; ES323530A1

Description

29, 1966 c. JENCKS ETAL 3,

DRAW-OUT SWITCH-GEAR INTERLOCK APPARATUS Filed March 1, 1965 5 SheetsSheet 1 INVENTORS CHARLES L. L/ENCK-S') FRANK H. MURPHY A TTORNEY Nov. 29, 1966 c. JENCKS ETAL 3,283,955

DRAW-OUT SWITCH-GEAR INTERLOCK APPARATUS 5 Sheets-Sheet 5 Filed March 1. 1965 m 0 T N E V m CHARLES L. Java/(s, kANK. H. MURPHY H M% C 17 A TTORNEY United States Patent 3,288,956 DRAW-OUT SWITCH-GEAR INTERLOCK APPARATUS Charles I... Jencks, Avon, and Frank H. Murphy, West Hartford, Conn, assignors to General Electric Comparty, a corporation of New York Filed Mar. 1, 1965, Ser. No. 435,885 2 Claims. (Cl. 200-50) This invention is concerned with draw-out switch gear apparatus and more particularly with such apparatus which includes an interlock arrangement adapted and disposed to prevent the disconnection of removably enaged main current carrying connectors unless the circuit has been interrupted through the actuation of appropriate switch means operatively engaged with the interlock means.

Accordingly, it is a principal object of the present invention to provide a draw-out switch gear apparatus of substantial current carrying capacity for connecting an electrical source to an electrical load and incorporating interlock means preventing the disconnection of such a draw-out switch gear when current is flowing therethrough.

Another object of the present invention is to provide such draw-out switch gear apparatus employing a circuit breaker as the switch means and having such circuit breaker operatively engaged with the interlock means so that the apparatus may not be withdrawn from electrical connection unless the circuit breaker is in its open circuit condition assuring that the flow of currents through the switch gear apparatus have been previously interrupted.

Another object of the present invention is toprovide such a draw-out switch gear apparatus including a circuit breaker wherein the interlock means is operatively responsive to its release position to prevent the movement of the main current carrying contacts of the circuit breaker to their closed circuit position.

The invention in one form comprises a draw-out switch gear apparatus including a support structure having fixed electrical connectors which are arranged to be connectable to an electrical source and fixed electrical connectors similarly supported and arranged to be connectable to an electrical load. The fixed support structure also includes means to removably receive a switch gear assembly having front and rear insulating walls carrying a plurality of electrical connectors in paired disposition and supporting fusible means and electrical conductors between the front and rear insulating walls. The switch gear assembly and its electrical connectors are so arranged as to be removably engageable in electrical circuit with the fixed source connectors and the fixed load connectors mounted upon the support structure. A circuit breaker is removably mounted on the front insulating wall of the switch gear assembly in electrical connection with the source connectors and load connectors carried by the front insulating wall. An interlock means is provided which extends through the front insulating wall and is configured so as to lock the switch gear assembly in engagement with the supporting structure and prevent its withdrawal therefrom. The interlock means in its preferred embodiment may comprise a rotatable shaft extending through the front insulating wall and having a handle means thereon arranged to be rotatably disposed in lock and release positions. Means are also provided to be engaged with the main contact operating mechanism of the circuit breaker and arranged to be responsive to the on and off conditions of the circuit breaker to be disposed in first and second positions, respectively, the first position preventing unlocking of the interlock means and the second position permitting unlocking of the interlock means.

In the preferred embodiment of the invention, the means operatively engaged to be responsive to the main contact operating mechanism of the circuit breaker to prevent or permit unlocking of the interlock means may take the form of a spring-loaded plunger which is disposed and arranged to retract out of the path of a radially disposed member on the rotatable interlock means when the circuit breaker is in its open circuit condition and to be positioned against its spring-bias into the path of the radially disposed member of the interlock means when the circuit breaker is in its closed circuit conditions.

Additionally, the preferred embodiment includes means responsive to the release position of the interlock mechanism to prevent closure of the circuit breaker main current conducting contacts.

These and other objects and features of the present invention will be more fully understood from the following detailed description together with the accompanying drawings' and its scope will be pointed out in the appended claims.

In the drawings:

FIGURE 1 is a perspective view of an embodiment of the present invention illustrating the draw-out switch gear apparatus in connection with an electrical source and an electrical load and in interlocked condition;

FIGURE 2 is a perspective view illustrating the male portion of the electrical connectors as they are disposed on a portion of the removable frame assembly of the draw-out switch gear apparatus of the present invention;

FIGURE 3 is a side elevational, partially cross-sectional view of an embodiment of the present invention illustrating the manner of connection of its main current carrying contacts and the operative engagement of the circuit breaker with the interlock means;

FIGURE 4 is a side elevational view of a portion of the interlock mechanism operatively engaged with the circuit breaker of the draw-out switch gear apparatus of the present invention;

FIGURE 5 is a perspective view showing the removable swi-tch gear assembly of the present invention in its unlocked and disengaged condition with the circuit breaker in it's open circuit position;

FIGURE 6 is a perspective enlarged view of the interlock mechanism of the present invention; and

FIGURE 7 is a perspective enlarged view of an arrangement for operatively engaging the interlock mechanism so as to position the removable switch gear assembly for special purposes such as testing the circuit breaker.

Referring now to FIGURE 1, there is shown a drawout switch-gear apparatus embodying the present invention and including a removable switch assembly 10 received and supported by a fixed support structure indicated generally at 11 which has a plurality of electrical conductors connected thereto in insulated arrangement such as the conductors 12, 13 and 14 which may be connected to a three-phase electrical source, for instance. Similar conductors are arranged on the mixed support structure 11 to be connectable to an electrical load. A switch gear assembly 10 is removably received in the fixed support structure and comprises a rear insulating wall 15 arranged to support electrical connectors therein and a front insulating wall 16 which similarly supports a like plurality of electrical connectors. Arranged and supported between the rear insulating wall 15 and the front insulating wall 16 are a plurality of fusible means such as the three fuses shown at 17, 18 and 19. The fusible means 17, 18 and 19 are connected to electrical connectors supported on the front insulating Wall 16 which are in turn adapted to be engaged in electrical connec- Patented Nov. 29, 1963.

tion with a removable circuit breaker 20 to supply the circuit breaker with a line source of electrical energy. A plurality of lower electrical connectors is carried by the front and real insulating walls with conductors connected therebetween for completing the circuit to an electrical load.

The circuit breaker 20 has a manually operable handle mechanism which extends through an aperature in the trim plate 21 as shown at 22. An interlock means illustrated generally at 23 is arranged to lock the switch gear assembly in removable engagement with the fixed support structure 11 so as to prevent its being drawn out unless the flow of current therethrough has been interrupted by actuation of the circuit breaker 20. This operation and its co-acting relationship will be explained more fully hereinafter. It should be noted that the interlock mechanism shown generally at 23 includes a handle 24 externally connected on the end of a shaft or rod 25 which is supported to be rotatable in accordance with the disposition of the handle 24 in its lock or release position. Adjacent the rear insulating wall 15, an L-shaped latch member 26 is carried by the rotatable shaft 25 and is shown in locking engagement with an aperture 27 in the fixed support structure 11, thus preventing the sliding withdrawal of the switch gear assembly 10 and disengagement of the electrical connectors carried by the rear insulating wall from the electrical connectors supported in insulated disposition on the fixed support structure 11 while current is flowing through the apparatus. A second handle 28 is provided on the trim plate 21 to afford two hand grips for slidingly withdrawing the switch gear assembly 10 of the draw-out switch gear from engagement with the fixed support structure.

FIGURE 2 shows in more detail the rear insulating wall of the removable switch gear assembly 10 and the plurality of electrical connectors supported upon it in insulated disposition. The

electrical connectors

29, 30, 31, 32, 33 and 34 are shown to be disposed and aligned on the insulating wall 15 in paired disposition. In a typical application of draw-out switch gear apparatus embodying the present invention, a three-phase electrical source may be connected to an appropriate electrical load and, in such case, the connector 29 is arranged to receive one phase of such electrical source while its paired connector 30 is disposed to be connectable to one phase of the electrical load to be supplied. Similarly, the pairs of contacts 31 and 32 are arranged and disposed to be connectable to the second phase of an electrical source and an electrical load, respectively. In the same manner, the remaining pair of electrical connectors 33- and 34 are arranged and disposed to be connected to the third phase of an electrical source and the electrical load, respectively. On the other side of the rear electrical insulating wall 15, the connectors 29, 31 and 33 are connected in circuit with fusible means such as the

fuses

17, 18 and 19 shown in figure 1, while the

electrical connectors

30, 32 and 34 are connected to straight-through electrical conductors which in turn, together with the fusible means, are connected in electrical engagement with a plurality of separately paired connectors on the front insulating wall 16 in a manner to be more fully described hereinafter.

Referring now to FIGURE 3, there is shown in side elevational, partially cross-sectional view, a draw-out switch gear apparatus generally of the type illustrated in perspective in FIGURE 1, and like members bear the same numerical designations as in FIGURE 1. As described in connection with FIGURE 2, the rear insulating wall 15 of the removable switch gear assembly 10 supports a number of electrical connectors such as 34 shown in sectional view in FIGURE 3. A fixed wall 35 of the fixed support structure 11 supports in insulated disposition a like number of tulip type connectors, such as that shown at 36, which are disposed and adapted to receivably engage in electrical connection the electrical connectors disposed on and extending from the rear insulating wall 15 of the removable switch gear assembly 10. As shown in FIGURE 3, the tulip connector 36 is electrically connected to a bus bar type of conductor 37 which is arranged to be connectable to an electrical load. In a similar manner, a bus bar type conductor 38 fixedly connected in electrical engagement with a tulip type electrical connector is disposed and arranged to be connected to one phase of a three-phase electrical source, for example. Typically, a draw-out switch gear apparatus of the type illustrated in FIGURES 1, 2 and 3 may include three bus bars and tulip type electrical connectors to be connectable to the three phases of an electrical source, while the lower portion of the draw-out switch gear apparatus will be provided with three conductors such as that shown at 37, arranged in electrical engagement with tulip type connectors and disposed to be connectable to a three-phase electrical load. The fixed support structure 11 also includes a rail 39 disposed to slidingly receive a rail 40 which is afiixed to and supports the removable switch gear assembly 10. Also included on the fixed support structure 10 is an aperture 27 which is disposed to receive in engagement an L-shaped radial ly movable latch member 26 arranged to engage the interlock means 23 with the fixed support structure 11 to prevent removal of the switch gear assembly 10 from electrical engagement with the electrical source and electrical load when current is flowing therethrough. The interlock means 23 in the embodiment illustrated in FIGURE 3 takes the form of a rod or shaft 25 supported upon the switch gear assembly 10 for rotation about its major axis and passing through the trim plate 21 and the front rear insulating walls 16 and 15, respectively. The front end of the shaft 25 of the interlock means 23 which passes through the trim plate 21 has affixed thereto an appropriate handle means 24 which is disposed to be rotated to lock or release positions. As shown in FIGURE 3, the handle 24 is disposed in its lock position and accordingly, the latch member 26 is received in engagement in the aperture 27 in the fixed support structure preventing withdrawal of the removable switch gear assembly 10 and consequent disconnection of the electrical connectors on its rear insulating wall 15 from the similarly disposed and complementary configured tulip type connectors disposed in insulated arrangement on the fixed support structure 11. The shaft 25 also carries a second radially disposed member 41 which is connected with a spring-bias means 42 adapted to retain the interlock means 23 in its locked position.

A circuit-breaker 20 is supported on the front insulating wall 16 in electrical engagement with electrical connectors engaged in circuit with the fusible means 17, 18 and 19 such as the one electrical connector 43 shown by the dash-line outline and a similarly disposed lower plurality of electrical connectors such as that shown at 44 by the dash outline which in turn are connected to a plurality of through conductors such as that shown at 45'. Suitable support means 46 and 47 support the trim plate 21 from the front insulating wall 16, the trim plate 21 having an aperture therein to permit the external, manually operable, reciprocal handle means 22 of the circuit-breaker 20 to pass therethrgugh. The circuitbrea'ker 20 includes at least one pair of relatively movable contacts such as the stationary contact 48 and the movable contact 49. Each movable contact such as 49 is supported upon a pivotable contact arm 51 which is arranged to engage and disengage the current-carrying contacts 48 and 49 upon movement of the contact arm 51 about its pivot point 52. Such actuation of the contact arm 51 may be effected by manual operation of the externally extending handle 22 or by appropriate current-,

sensitive means included in the circuit breaker which may be either magnetically or thermally responsive to the flow of predetermined overload currents to automatically operate the main operating mechanism of the circuit breaker to disengage its current carrying contact, such as the single pair of contacts shown at 48 and 49. The illustration of FIGURE 3 shows the circuit-breaker 20 as having its handle 22 in the on position and accordingly, the main current carrying contacts are disposed in electrical engagement with the contact arm 51 restrained in its latched position by appropriate means (not shown). Also supported upon the front insulating wall 16 is a bracket 53 which supports thereon a rod member 54 which is spring biased by an appropriate spring means 55 so as to perform in the manner of a plunger biased toward movement to the left in the illustration of FIGURE 3. The plunger 54 is shown to be inmechan-ical contact with the contact arm 51 and, accordingly, is arranged to be displaced to the right or to the left in accordance with the disposition of the contact arm 51 and the open or closed circuit condition of the relatively movable contacts 48 and 59. As illustrated in FIGURE 3, the end portion 54a of the plunger 54 is disposed in the rotational path of member 41 so as to block the rotation of the interlock means 23, restraining its latch member 26 in engagement with the aperture 27, thus preventing the sliding removal of the switch gear assembly from electrical engagement with the plurality of electrical connectors carrying line and load currents as was previously described. Upon actuation of the circuit breaker to its off position, the pivotable contact arm 51 pivots to the left in FIGURE 3 allowing the plunger 54 to be moved to the left in response to its spring bias so that the end portion 54a of the plunger 54 is clear of the rotational path of the radially disposed member 41 of the interlock means 23, permitting the interlock means 23 to be rotated by means of its handle 24 from its lock to its release position, thus disengaging the latch member 26 from restraining engagement in the aperture 27 and permitting the disengagement of the plurality of electrical connectors carried on the rear wall of the switch gear assembly and the insulated wall of the fixed support structure. As will be apparent to those skilled in the art, under these conditions, the electrical disengagement of the electrical connectors on the rear of the draw-out switch gear apparatus is permissible without undue danger or arcing due to the fact that the flow of current through the apparatus has neces sarily previously been interrupted by actuation of the circuit-breaker from its on to its off position so that the main current-carrying contacts of the circuit-breaker 20 such as those shown at 48 and 49 are disposed in their open circuit posit-ion FIGURE 4 illustrates the circuit-breaker 20 in its open circuit condition so that the interlock means 23 may be positioned in its release position permitting withdrawal of the removable switch-gear assembly from electrical engagement with electrical connectors of the fixed support structure. In FIGURE 4, like members bear the same numerical designations as in FIGURES 1, 2 and 3. The pivot'able contact arm 51 of the circuit-breaker 20 is shown as having pivoted to the left permitting the plunger 54 to move to the left against the bias exerted upon it by the spring 55, thereby displacing the plunger 54 and its end portion 5411 out of the rotational path of the radially disposed member 41 carried by the shaft of the interlock means 23. As may be noted in' FIG- URE 4, the externally extending, reciprocally operable handle member 22 of the circuit breaker-20 is disposed in its oil condition consistent with the open circuit condition of the current-carrying contacts 48 and 49. Thus, the flow of currents through the draw out switch gear apparatus has been interrupted prior to the interlock mean and its co-acting elements being disposed to permit unlatching disengagement of the interlock means and withdrawal of the removable switch gear assembly from electrical engagement with fixed electrical source and electrical load connectors carried by the fixed support structure.

FIGURE 5 illustrates the draw-out switch gear assembly of the present invention \as embodied in the previously described figures, but in its disengaged, withdrawn condition. In FIGURE 5, like members bear the same numerical designations as in FIGURES l, 2, 3 and 4. The switch gear assembly 10 supported on its rail 40 is seen to have been disengaged from electrical connection of its plurality of electrical connectors extending beyond the rear insulating wall 15 with the plurality of tulip type connectors disposed in fixed aligned position on the fixed support structure 11.

It should be noted that the handle 24 of the interlock means 23 is disposed in its release position by reason of having been rotated in a clockwise direction. Thus, the latch member 26 has been disengaged from the aperture 27 carried by the fixed support structure 11 as previously described in connection with FIGURES 1 and 3, permitting the switch gear assembly 10 to be slidingly withdrawn. An appropriate stop means as shown at 56 falls into a latched posit-ion upon withdrawal of the switch gear assembly and prevents inadvertent complete removal from the support of the rails of the fixed support structure 11 such as the rails shown at 39, for example. If it is desired to completely remove the switch gear assembly 10, the latch means 56 may be manually disengaged to permit the entire switch gear assembly 10 to be completely withdrawn from support of the rails of the fixed support structure 11. The plurality of tulip type electrical connectors disposed and arranged on the fixed support structure 11 as shown at 57, 5-8, 59, 60 and 61 each comprise a plurality of electrically conductive members arranged circularly such as shown at 57a, and surrounded by an appropriate spring means such as that shown at 57b so as to urge the plurality of conductive members 57a toward the center of the connector thus assuring secure and positive electrical contact with a minimum of electrical and mechanical re sistance upon the insertion of electrical connectors of the type shown at 29, 30, 31, 32, 33 and 34 in FIGURE 2 into electrical connection with the tulip type electrical connectors.

As will be apparent to those skilled in the art, the use of the tulip type connectors not only assures a secure and positive electrical contact but also permits convenient and ready disengagement of those electrical connectors when such disengagement is desirable and the interlock means of the apparatus of the present invention has been suitably positioned to allow such disengagement in the manner previously described.

A further advantage of the present invention is the feature of its interlock means by reason of which it co-acts with the circuit break of the switch-gear assembly to prevent closure of the relatively movable contacts of the circuit breaker to effect its closed circuit condition when the interlock means is disposed in its release position. Referring now to FIGURE 6, it may be seen that the interlock means 23 has its handle 24 in the lock position. Thus, the latch 26 is disposed to be engaged with a locking aperture in the fixed support structure in a manner previously described. The plunger 54, it will be recalled from the description in connection with FIGURE 3, is operatively responsive to the position of the pivotable contact arm 51 of the circuit breaker 20 as shown in FIGURE 6 to be retracted out of the path of the rotatable, radially disposed member 41 carried by the interlock means23, thus indicating that the circuit breaker has its external handle 22 positioned in an off position and that the relatively movable main current carrying contacts of the circuit breaker are in their open circuit condition. As the interlock means 23 is disposed in its release position, the handle 24 is turned in a clockwise direction; and, as a consequence, the radially disposed member 41 of the interlock means is carried into a position directly in the path of the plunger 54 so that the plunger 54 may not be moved inwardly against its spring bias. Accordingly, the

movable contact arm such as 51 as shown in FIGURE 3 of the circuit breaker 20 may not be moved to its closed circuit position by reason of the plunger 54 preventing such pivotal movement. Thus, as conceived by the present invention, the interlock means not only prevents the switch-gear assembly from being removed from electrical engagement with line and source connectors carried by a fixed support structure but also it prevents the closure of a switch means such as a circuit breaker carried by the switch-gear assembly when the interlock means is in the release position.

A further feature of the present invention which is adapted to permit test procedures such as testing the operation of the circuit breaker is shown in FIGURE 7. It is sometimes necessary or desirable to test the operation of the switching apparatus incorporated in the removable switch-gear assembly of the present invention, and during such procedures it is desirable that the switch-gear assembly be disconnected from electrical engagement with line and source connectors carried by the fixed support structure. For this purpose the present invention conceives a latch means carried by the fixed support structure which is adapted to secure the removable switch-gear assembly in a disengaged but relatively fixed position to prevent its sliding on its support rails during such test procedure. As shown in FIGURE 7, a portion of the fixed support structure 11 carries an aperture 27 with which a latch member 26 of the interlock means 23 is normally engaged when the removable switch-gear assembly 10 of the present invention is in electrical engagement with the line and source connectors carried by the fixed support structure 11 of the draw-out switch-gear apparatus. If it is desired to test the operation of the switch-gear carried by the apparatus, however, the interlock means may be disengaged from its lock position as has previously been described, and the removable switch-gear assembly drawn out partially with the interlock means allowed to return to its lock position. The latch 26 carried by the rod 25 of the interlock means 23 will then engage a latch 56 as shown in FIGURE 7 which is so configured and disposed as to prevent either further withdrawal of the removable switchgear assembly or its sliding movement in the opposite direction toward electrical engagement of its electrical connectors with those carried by the fixed support structure. Thus, for purposes of test procedures, the removable switch gear assembly remains in a disengaged but relatively fixed position as desired.

As it will be appreciated by those skilled in the art, the present invention not only provides an interlock means which prevents inadvertent disengagement of heavy current carrying contacts by arranging that such disengagement may only be effected after the flow of current therethrough has been interrupted by appropriate means such as a circuit breaker, but also provides that the circuit breaker, but also provides that the circuit breaker or other appropriate switch-gear may not be positioned from its open circuit to its closed circuit position when the interlock means is in a release position. Additionally, the features of a fixed disengagement as may be desirable for test procedures are included within the concept of the present invention and afiford a convenient and desirable means of achieving additional objects and features of an interlock means for heavy circuit carrying draw-out switch-gear apparatus including a removable switch-gear assembly and usually incorporating a circuit breaker or similar appropriate switch means as well as fusible means.

While we have disclosed only certain embodiments of the invention, it will be readily appreciated that many modifications thereof may be made. We therefore intend by the appended claims to cover all such modifications as fall within the true spirit and scope of the invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. Drawout electrical switchgear apparatus comprising:

( a ain s ppor (b) a secondary support;

(0) said main support and said secondary support including cooperating means slidably supporting said secondary support for reciprocal movement on said main support in a predetermined direction;

(d) an electrical control device mounted on said secondary support for movement therewithin between inserted and retracted positions, said control device including at least one contact member and a manually operable handle movable between open and closed circuit positions and means connecting said handle tosaid movable contact to move said contact to open and closed circuit positions upon movement of said handle to said open and closed circuit positions respectively;

(e) interlock means preventing movement of said secondary support so as to move said electrical control device from said inserted toward said retracted position while said movable contact member is in said closed circuit position;

(f) said interlock means comprising an elongated rod carried by said secondary support member, said rod extending substantially in said predetermined direction;

g) manually operable handle means connected to said rod for rotating said rod between an interlocking position and a releasing position;

(h) a first extension extending from said rod and extending into an aperture in said main support when said secondary support is in a position corresponding to said inserted position of said control device;

(i) a second extension on said rod;

(j) a blocking member movably carried by said control device and means interconnecting said movable contact member and said'blocking member and moving said blocking member to a blocking position when said contact member is in said closed circuit position and moving said blocking member to a non-blocking position when said movable contact is in said open circuit position;

(k) said blocking member when in said blocking position obstructing movement of said second extension of said rod to thereby obstruct movement of said rod such as to move said first extension out of said aperture when said circuit control device is in said inserted position;

(1) means engaging said interlock means and retaining said elongated rod of said interlock means in said releasing position while said circuit breaker is in a position other than said inserted position;

(m) said second extension being positioned in the path of movement of said blocking member while said interlocking rod is in said releasing position;

(11) said blocking member engaging said second extension and preventing movement of said movable contact member to said closed circuit position while said interlocking rod is in said releasing position.

2. Drawout electrical switchgear apparatus as set forth in claim 1, wherein said blocking member comprises a rigid plunger slidably carried by said electric control device and means biasing said blocking member toward said nonblocking position at all times, said movable contact member engaging said plunger as said movable contact member moves toward said closed circuit position to overcome said biasing means and move said blocking member toward said blocking position.

References Cited by the Examiner UNITED STATES PATENTS 3,005,064 10/1961 Baird et al 20050.15

BERNARD A. GILHEANY, Primary Examiner.

H. A. LEWITTER, Assistant Examiner.

Claims

1. DRAWOUT ELECTRICAL SWITCHGEAR APPARATUS COMPRISING: (A) MAIN SUPPORT; (B) A SECONDARY SUPPORT; (C) SAID MAIN SUPPORT AND SAID SECONDARY SUPPORT INCLUDING COOPERATING MEANS SLIDABLY SUPPORTING SAID SECONDARY SUPPORT FOR RECIPROCAL MOVEMENT ON SAID MAIN SUPPORT IN A PREDETERMINED DIRECTION; (D) AN ELECTRICAL CONTROL DEVICE MOUNTED ON SAID SECONDARY SUPPORT FOR MOVEMENT THEREWITHIN BETWEEN INSERTED AND RETRACTED POSITIONS, SAID CONTROL DEVICE INCLUDING AT LEAST ONE CONTACT MEMBER AND A MANUALLY OPERABLE HANDLE MOVABLE BETWEEN OPEN AND CLOSED CIRCUIT POSITIONS AND MEANS CONNECTING SAID HANDLE TO SAID MOVABLE CONTACT TO MOVE SAID CONTACT TO OPEN AND CLOSED CIRCUIT POSITIONS UPON MOVEMENT OF SAID HANDLE TO SAID OPEN AND CLOSED CIRCUIT POSITIONS RESPECTIVELY; (E) INTERLOCK MEANS PREVENTING MOVEMENT OF SAID SECONDARY SUPPORT SO AS TO MOVE SAID ELECTRICAL CONTROL DEVICE FROM SAID INSERTED TOWARD SAID RETRACTED POSITION WHILE SAID MOVABLE CONTACT MEMBER IS IN SAID CLOSED CIRCUIT POSITION; (F) SAID INTERLOCK MEANS COMPRISING AN ELONGATED ROD CARRIED BY SAID SECONDARY SUPPORT MEMBER, SAID ROD EXTENDING SUBSTANTIALLY IN SAID PREDETERMINED DIRECTION; (G) MANUALLY OPERABLE HANDLE MEANS CONNECTED TO SAID ROD FOR ROTATING SAID ROD BETWEEN AN INTERLOCKING POSITION AND A RELEASING POSITION; (H) A FIRST EXTENSION EXTENDING FROM SAID ROD AND EXTENDING INTO AN APERTURE IN SAID MAIN SUPPORT WHEN SAID SECONDARY SUPPORT IS IN A POSITION CORRESPONDING TO SAID INSERTED POSITION OF SAID CONTROL DEVICE; (I) A SECOND EXTENSION ON SAID ROD; (J) A BLOCKING MEMBER MOVABLY CARRIED BY SAID CONTROL DEVICE AND MEANS INTERCONNECTING SAID MOVABLE CONTACT MEMBER AND SAID BLOCKING MEMBER AND MOVING SAID BLOCKNG MEMBER TO A BLOCKING POSITION WHEN SAID CONTACT MEMBER IS IN SAID CLOSED CIRCUIT POSITION AND MOVING SAID BLOCKING MEMBER TO A NON-BLOCKING POSITION WHEN SAID MOVABLE CONTACT IS IN SAID OPEN CIRCUIT POSITION, (K) SAID BLOCKING MEMBER WHEN IN SAID BLOCKING POSITION OBSTRUCTING MOVEMENT OF SAID SECOND EXTENSION OF SAID ROD TO THEREBY OBSTRUCT MOVEMENT OF SAID ROD SUCH AS TO MOVE SAID FIRST EXTENSION OUT OF SAID APERTURE WHEN SAID CIRCUIT CONTROL DEVICE IS IN SAID INSERTED POSITION; (L) MEANS ENGAGING SAID INTERLOCK MEANS AND RETAINING SAID ELONGATED ROD OF SAID INTERLOCK MEANS IN SAID RELEASING POSITION WHILE SAID CIRCUIT BREAKER IS IN A POSITION OTHER THAN SAID INSERTED POSITION; (M) SAID SECOND EXTENSION BEING POSITIONED IN THE PATH OF MOVEMENT OF SAID BLOCKING MEMBER WHILE SAID INTERLOCKING ROD IS IN SAID RELEASING POSITION; (N) SAID BLOCKING MEMBER ENGAGING SAID SECOND EXTENSION AND PREVENTING MOVEMENT OF SAID MOVABLE CONTACT MEMBER TO SAID CLOSED CIRCUIT POSITION WHILE SAID INTERLOCKING ROD IS IN SAID RELEASING POSITION.