GB2111631A - Electrical bay security device - Google Patents

Abstract

An electrical bay unit has a disconnect switch which is switched off automatically when the bay door is opened. Mechanics or testers will often wish to switch on the unit independently of the door, e.g. using tools. However, such defeat of the automatic disconnect can lead to catastrophe if attempts are made to replace the unit in the bay with the switch on, at connect. To avoid this, a switch operated interlock tongue 3 is moved via a pin 10 in a slot 11 with transverse clearance, to interlock with a recess in a rail 2. At interlock the unit can no longer slide in and out of the bay on the rail. The tongue is part of a plate 5 in which the slot is cut, and which slides vertically between locking and unlocking positions between pins 6, 7, 8 and 9 which have circumferential grooves to guide the horizontal edges of the plate. This interlock is governed only by the disconnect switch and is practically undefeatable, howsoever the skilled man may manipulate the switch. <IMAGE>

Description

SPECIFICATION Electrical bay security device The present invention relates to electrical units arranged in bays. In general a column of similar or dissimilar units will be mounted between vertical structure members. The units will be individually removable on respective horizontal supports in the manner of drawers in a cupboard or chest of drawers. The horizontal supports are usually mounted on the vertical structure members. Usually a bay will contain several columns of units.

Also usually, the individual units cannot be removed without opening individual doors, and the action of opening or unlocking the doors is often arranged in the interests of personal or equipment security to switch off the electrical power to the unit by means of a disconnect switch.

The personal safety issue arises because portions of the unit are usually electrically live unless the disconnect switch is at 'off'. The door when closed prevents danger from live portions if the unit is in operation. Contacts at the rear of the unit will engage fixed energizing contacts within the bay whenever the unit is fully home, but the disconnect switch enables removal in safety. Equipment security arises for instance if alien metal objects can contact the units while these are live and cause short-circuits.

Another aspect arises if attempts are made to remove orto replace the unitwhilethe disconnect switch is 'on' and so the unit can take full operating current. The full carrent is then made or broken at the bay contacts by the action of replacing or removing the unit. This can cause arcing and hence damage to the bay contacts which are not generally designed as switch contacts. Such arcs can cause damaging electrical surges within the unit itself or in other equipment in the bay.

Engineers will often attempt to defeat disconnects of the door-operated type in the short-term interests of checking electrical parameters in situ, eg. with the unit fully in the bay and operating. For instance the action of unlocking the door may rotate a spindle or shaft of the disconnect switch, which rotation can easily be reversed by the engineer with pliers or other tools. Such defeating actions are sometimes highly to be deprecated, in case eg. relatively unqualified or careless engineers subsequent remove or replace current - carrying units with the automatic disconnect switch still 'on'. Replacing the units especially can cause damaging surges by arcing before the full current is taken. The invention aims to allow defeat of an automatic - disconnect while reducing or eliminating such risk of surging or arcing damage.

A particular type of unit very often arranged in bays is the motor control unit. Many motors throughout a factory or other large area installation may be controlled from one central bay. Buses behind the bays will distribute the individual control andlor energizing currents to the individual motors of the factory. The whole operation of such a central control bay should therefore be of high integrity, and the invention aims to maintain or improve safety and security while if desired allowing engineers to defeat door-operated or other automatic or remotely - controlled security disconnect switches in a unit, in the interest of testing etc.

It has been proposed in U.S. Patent 4,002,865 to move a bay unit only by a removably engaged levering crank, and to condition insertion or removal of the crank itself according to the position of the unit or its disconnect interruptor or an access door.

However, such complications are undesirable and it was preferred that the switch itself govern removability, be door - operated, and yet be easily manipulated when required by the service man independently of the door. German DAS-1082327 discloses an interlock which is not automatic, although it prevents moving a bay unit when a disconnect switch is on. It gives no hint either of a door-operated switch, or of an automatic interlock.

According to the present invention, there is provided electrical bay equipment comprising a bay unit energizable through a disconnect switch, a bay for receiving the bay unit at an operational position for its energization, a door having an open condition, and a closed condition preventing any manipulation or removal or replacement of the unit with respect to its operational position, an interlock member movably mounted on the unit and moved into a locking position whenever the disconnect switch is turned on, interlock means mounted in the bay to hold the interlock member when the latter is in its locking position against either said removal or said replacement thereof, and automatic coupling means on the door for turning the switch to disconnect whenever the door ceases to be in its closed condition; the disconnect switch being so arranged that it can be manipulated other than by the door coupling means by that the condition of the disconnect switch undefeatably determines the position of the interlock member.

According to a main feature of the present invention there is provided an electrical unit removably locatable in a bay, disconnect switch associated with the individual unit, and a mechanical interlock operated by operation of the disconnect switch, whereby the unit cannot be either removed from an operable position in the bay, or operatively replaced in the bay, unless the disconnect switch is in its 'off' condition of electrical de-energization of the unit.

According to a preferred advantageous embodiment of the invention the disconnect switch is automatically engageable by the lock or latch of a door giving manual access to the unit so as normally to be 'off' when said manual access is available, and such automatic engagement of the switch can be defeated by engineers according to a non-routine manoeuvre, but such non-routine defeating of the access - controlled engagement in order to produce an 'on' condition of the disconnect switch is not effective to allow removal or replacement of the unit with respect to an operational position within the bay. Such non-routine manoeuvres may be deliber ately designed for, or merely be a known or obvious accidental feature of the switch design.

An "operational position" in this context signifies that electrical engagement of the unit with energiz ing contacts in the bay has been set up by the unit having been inserted fully home in the bay.

Further objects, features and advantages of the present invention will appear from the following description of embodiments, given by way of example in conjunction with the drawings in which: Figure 1 shows a plan and Figure 2 a side view of a mounting plate: Figure 3 shows a side view and Figure 4 a plan of an interlock drive plate; Figures 5 and 6 show side views respectively of a drive pin alone, and of this drive pin inserted into the drive plate of Figures 3 and 4: Figure 7 is a side view of a guide pin; Figure 8 shows an interlock plate in plan view; and Figure 9 shows, in a plan view of part of a motor control unit, those items illustrated in Figures 1-8 in an interlock assembly portion of the unit.

Referring briefly to Figure 9 first, a motor control unit 1 has extremities approximately defined by apices A,B,C,D,E,F. It rests on two support rails which are horizontal and only one of which is shown at 2. A tongue 3 projects from unit 1 into a slot, depression, cut-out or castellation in rail 2 when interlocking engagement is required. The tongue may be withdrawn, upwards as viewed, so as only to extend "downwards" as far as the dotted line 4 when interlocking is not required, so that the tongue is free from rail 2. The tongue 3 is part of an interlocking plate 5 which can slide up and down as viewed, in fact horizontally, between guide pins 6,7, 8 and 9. The sliding motion is set up by a drive pin 10 which projects through a rectangular orifice 11 in plate 5.These parts provide interlocking in response to rotations of a disconnect switch, and are all mounted on a mounting plate 12 which is secured to unit 1 and the mounting is described further below.

In the Figure 9 plan view, insertion of the unit into its functional position whereat it contacts a live bus (not shown) is manually, in the direction of arrow 13 parallel with rails 2. Either insertion, or removal in the opposite direction of the arrow, is prevented whenever the interlock plate 5 is positioned as shown with the tongue 3 engaged in rail 2. When the drive pin 10 is in its second position 10', it has slid the interlock plate 5 over the mounting plate 12 until the tongue only extends to position 4 and is disengaged from the rail 2.

There may be third position 10" of drive pin 10, at which the slot 11 has been driven to the position 11" for testing purposes or other reasons, but this does not concern the invention. The further sliding of the interlock plate will draw tongue 3 even further away from engagement with rail 2.

Referring now to Figures 1 and 2, the mounting plate 12 has a flange 13 for its fixing on unit 1 or other slidable bay equipment to be protected, four tapped holes 14 for screwing in the guide pins 6-9 and a hole 15 through which there passes a rod (not shown) which rotates in response to repositionings of a disconnect switch but which does not move otherwise. One of the guide pins 6 is shown in Figure 7.

Attached to the rotating rod and therefore centred over hole 15 is a drive plate 16, see Figures 3 and 4.

This has an axial portion 17 with a bore 18 and a tapped entry 19 for a set-screw attachment to the switch - driven rod in hole 15 of the mounting plate.

The drive plate also has a plate portion 20 which thus rotates also with the rod and which, via a tapped or clearance hole 21, carries eccentrically the drive pin 10 of Figure 9. As the drive plate 16 is rotated with the switch, therefore, the drive pin rotates. In one preferred arrangement the switch has two positions, ie. on and off, and drive pin rotates 90 between these two switch conditions (see position 10' in Figure 9).

Referring to the Figure 5 side view, pin 10 is seen to have a tapped portion 22 for engagement with hole 21 of the drive plate and a projecting portion 23 which drives the interlock plate 5 of Figures 1 and 8.

Portion 22 may be a clearance in hole 21 if preferred and project th rough for engagement and fixing by a circular spring clip if preferred. The set - screw hole 19 is then preferably offset circumferentially from the hole 21 in the drive plate.

Figure 6 shows a side view of the drive pin 10 in position in the drive plate 16, so that portion 23 can provide an eccentric or cam for linearly sliding the interlock plate 5 and its locking tongue end 3.

Referring to Figure 9 and Figure 8 the rectangular slot 11 is threaded over the drive pin 10, and the long dimension of slot 11 accommodates without effective engagement the movement in one direction (perpendicular to the intended linear drive) of the drive pin 10. The component movements of the drive pin along the direction of the intended linear drive engage the long sides of slot 11 and drive the interlock plate 5 into or out of engagement with rail 2, see Figure 9.

The sliding movement of the interlock plate 5 on the mounting plate 12 is constrained by the four guide pins 6,7,8 and 9 to be linear, by virtue of accommodating circumferential grooves in the guide pins, one groove 24 being shown in pin 6, by Figure 7. Therefore the movement of the interlock plate need not be horizontal, and certainly need not be transverse to the horizontal sliding movement of the motor control or other bay unit 1 itself. Engagement need not be with the rails 2, but with some other fixed bay portion. This is because the interlock plate 5 is captive in the four grooves of the guide pins. Plate 5 conveniently does move horizontally, however, in response to rotations of a vertically disposed rod as illustrated and presently preferred.

It is clear that the switch (not shown) need not be door - operated, in fact it need not be automatic at all. However, it is useful to have a switch which is normally accessible only to automatic means, but which can be manipulated somehow, mechanically or otherwise, by the service engineer or other specialist. Since the removed (or in position) unit may then be subjected to attempts to replace (or remove) it with the switch 'on', and since such attempts could cause equipment damage or even catastrophic short-circuiting of the bus-bar power source of the bay installation (consider for instance a carelessly left tool in the motor control unit shorting terminals therein), such attempts are prevented according to embodiments of the present invention.

An interlock, whether purely mechanical as illustrated or otherwise, is set up whenever the switch is 'on', and the unit cannot be moved from an operating position. Conversely, it cannot be replaced into an operating position. Once out on the bench, the apparatus can be switched - on after repairs etc. or for testing and servicing by competent personnel defeating the automatic switch.

Although the figures illustrate a drive pin 10 which rotates, the invention is not restricted to switches which are operable by a rotation, or turning movement. Switches with linear movements or other operations can similarly be operated to disconnect, or connect, by the operation of a door, and thereby operate also a detent or the like via an interlock.

Claims (6)

1. Electrical bay equipment comprising a bay unit energizable through a disconnect switch, a bay for receiving the bay unit at an operational position for its energization, a door having an open condition, and a closed condition preventing any manipulation or removal or replacement of the unit with respect to its operational position, an interlock member movably mounted on the unit and moved into a locking position whenever the disconnect switch is turned on, interlock means mounted in the bay to hold the interlock member when the latter is in its locking position against either said removal or said replacement thereof, and automatic coupling means on the door for turning the switch to disconnect whenever the door ceases to be in its closed condition; the disconnect switch being so arranged that it can be manipulated other than by the door coupling means but that the condition of the disconnect switch undefeatably determines the position of the interlock member.

2. Equipment according to claim 1 wherein the interlock member is a tongue linearly moved to engage the interlock means, and the switch is rotatable between on and off, and a coupling arrangement converting such rotational movements of the switch to linear motions of the tongue.

3. Equipment according to claim 2 wherein the tongue is part of an interlocking plate which is contrained to slide in one dimension, and a drive pin rotated by the switch and projecting into an orifice in the interlocking plate,has lost motion relative to the orifice in a direction transverse to said dimension of slide.

4. Equipment according to claim 2 or 3 wherein the movement of the unit with respect to its operational position is on a rail, and a slot, depression, cut-out, or castellation in the rail provides said interlocking means in the bay.

5. Equipment according to any one of claims 1 to 4wherein the bay unit is a motor control unit.

6. Bay equipment substantially as hereinbefore described with reference to any or all of Figures 1 to 9.