AU2007264396A1 - Rotary switch interlock - Google Patents

Description

WO 2008/000022 PCT/AU2007/000881 ROTARY SWITCH INTERLOCK FIELD OF INVENTION The present invention relates to rotary switchgear (typically, but not limited to, 5 under-oil rotary sectionalizing switches mounted inside a transformer tank that is an integral part of a compact electrical distribution substation). BACKGROUND OF THE INVENTION Rotary switch gear, such as under-oil rotary sectionalising switches mounted 10 inside a transformer tank, typically have three switching positions based at 90 degrees apart. Typically, such switch gear requires the switching handle to be rotated approximately 45 degrees past the target switching position in order for it to switch to the target switching position. This "over-rotation" is necessary for the internal spring-operated mechanism of such switch gear to be sufficiently pre-loaded in order 15 for it to switch to the target switch position. This is illustrated progressively in Figures 3a to 3c. With current switch gear of the type described above, it is possible for an operator to rapidly switch between the three positions of 'On', 'Off' and 'Earth'. In 20 practice, and in some circumstances, this rapid switching could result in a very dangerous and possibly explosive situation. For example, an operator may switch a live electrical cable from the 'Off' position to the 'Earth' position (thus creating a faulted situation) and then immediately switch back to the 'Off' position (thus creating an electric arc under oil). If the energy of the electrical arc is of sufficient 25 magnitude, then the rotary switch is unlikely to successfully "break" because of the arc thereby creating a dangerous (that is, explosive) situation. It is an object of the invention to address the above-mentioned problems or at least to offer a useful choice. 30 -1 - WO 2008/000022 PCT/AU2007/000881 SUMMARY OF THE INVENTION According to the invention there is provided a rotary switch interlocking assembly mountable to a multi-position rotary switch having a shaft and a switch body, the interlocking assembly including: 5 a switch actuator operatively connected to the shaft for rotation therewith about a switch axis; a limit body mounted for rotation with respect to the switch body; a locking arrangement between the limit body and the switch body, the locking arrangement operable to lock rotational movement of the limit body with 10 respect to the switch body at a plurality of angularly spaced apart positions; cooperating first and second clockwise limit stops, the first clockwise limit stop rotating with the shaft and the second clockwise limit stop mounted to or integral with the limit body, the first and second clockwise limit stops arranged to limit the clockwise angular rotation of the shaft with respect to the limit body; and 15 cooperating first and second anticlockwise limit stops, the second anticlockwise limit stop rotating with the shaft and the first anticlockwise limit stop mounted to or integral with the limit body, the first and second anticlockwise limit stops arranged to limit the anticlockwise angular rotation of the shaft with respect to the limit body; 20 whereby when the limit body is locked in any one of the plurality of circumferentially spaced apart positions, the limit stops limit rotation of the rotary switch shaft to a particular angular range. Preferably the particular angular range is such that an operator can only switch 25 between two switch positions while the limit body is locked in any one of its plurality of circumferentially spaced apart positions. Preferably the particular angular range is between 120 and 150 degrees. 30 Preferably the particular angular range is between 125 and 145 degrees. -2- WO 2008/000022 PCT/AU2007/000881 Preferably the particular angular range is between 130 and 140 degrees, and most preferably is approximately 135 degrees. Preferably the switch actuator is a boss. 5 Preferably the boss terminates in a bifurcated end defining a transverse slot through a cylindrical wall, whereby an anti-reflex handle can be mounted within the bifurcated end for actuation of the switch. 10 Preferably the locking arrangement includes an arm operatively connected to the shaft or the switch actuator for rotational movement therewith. Preferably the arm has a first limit stop surface and a second limit stop surface, 15 the first and second limit stop surfaces spaced apart from each other, whereby the first and second limit stop surfaces form the first clockwise limit stop and the second anticlockwise limit stop respectively. Preferably the limit body supports a first stop pin and a second stop pin, the 20 first and second stop pins spaced apart from each other, whereby the first and second limit stop pins form the first anticlockwise limit stop and the second clockwise limit stop respectively. Preferably the limit body is a limit plate. 25 Preferably the locking arrangement includes a detent arrangement. Preferably the detent arrangement includes a detent member mounted to prevent circumferential movement while allowing movement in a radial direction 30 with respect to the switch axis and a plurality of spaced apart notches within a arcuate edge on the limit plate, the notches arranged to selectively receive the detent -3- WO 2008/000022 PCT/AU2007/000881 member so as to lock movement of the limit plate with respect to the detent member against circumferential movement about the switch axis. An assembly as claimed in claim 13 wherein the detent arrangement includes a 5 detent spring, the spring biasing the detent member into engagement with the notches, wherein the detent member is manually movable so as to hold it out of any of the notches thereby allowing manual rotation of the limit plate with respect to the switch body. 10 Preferably the arcuate edge is concave and the spring biases the detent member radially outwards with respect to the switch axis. Preferably the assembly further includes a limit plate locking arrangement, the limit 15 plate locking arrangement allowing for locking the limit plate such that it can only be rotated between two of three positions. Preferably the limit plate locking arrangement includes an arcuate groove or slot within the locking plate and a padlock shackle, the shackle lockable to a tab 20 mounted to the switch body. A specific embodiment of the invention will now be described in some further detail with reference to and as illustrated in the accompanying figures. This embodiment is illustrative, and is not meant to be restrictive of the scope of the 25 invention. DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION A preferred embodiment of the invention is illustrated in the accompanying 30 representations in which; -4- WO 2008/000022 PCT/AU2007/000881 Figure 1 shows an isometric view of a rotary switch interlocking assembly mounted to a multi position rotary switch, the rotary switch mounted inside a transformer tank. Figures 2a, 2b and 2c show the front, side and top views respectively of the 5 interlocking assembly shown in Figure 1 as well as the side view of typical under-oil switchgear. Figures 3a, 3b and 3c are diagrammatic front views of the interlocking assembly of Figure 1 illustrating progressive angular movement between a starting position and a target position. 10 Figures 4a and 4b show front and side views of a base plate and a locking tag assembly of the interlocking assembly shown in Figure 1. Figures 5a and 5b show the front and side views respectively of a limit plate and stop pin assembly of the interlocking assembly shown in Figure 1. Figure 6 shows a side view of the arm and the switching boss assembly of the 15 interlocking assembly shown in Figure 1. Figures 7a and 7b show the front and side views of the selector assembly of the interlocking assembly shown in Figure 1. Figures 8a, 8b and 8c show the front views of the interlock assembly of Figure 1 when it is separately locked in the 'Earth', the 'Off' and the 'On' positions. 20 Figures 9a and 9b show the front views of the interlock assembly of Figure 1 when it is locked-out of the 'Earth' position so that switching operations are only possible between the 'Off' and the 'On' positions, and vice versa. Figures 10a and 10b show the front views of the interlock assembly of Figure 1 when it is locked-out of the 'On' position so that switching operations are only 25 possible between the 'Earth' and the 'Off' positions, and vice versa. Figures 11a, 11b and 11c are front views of the interlock assembly of Figure 1 showing the detent arrangement positioned to allow rotation of the switching boss, and hence rotary switch, from the 'Earth' position to the 'Off' position. Figures 12a, 12b and 12c are front views of the interlock assembly of Figure 1 30 showing the detent arrangement positioned to allow rotation of the switching boss, and hence rotary switch, from the 'Off' position to the 'On' position. -5- WO 2008/000022 PCT/AU2007/000881 Figures 13a, 13b and 13c are front views of the interlock assembly of Figure 1 showing the detent arrangement positioned to allow rotation of the switching boss, and hence rotary switch, from the 'On' position to the 'Off' position. Figures 14a, 14b and 14c are front views of the interlock assembly of Figure 1 5 showing the detent arrangement positioned to allow rotation of the switching boss, and hence rotary switch, from the 'Off' position to the 'Earth' position. Referring to Figures 1, 2a, 2b, and 2c a rotary switch interlocking assembly 30 mountable to a multi-position rotary switch 1 is shown. The rotary switch 1 is a 10 typical under-oil rotary sectionalising switch mounted on the inside of a transformer tank having a wall 4. The rotary switch has a shaft 3 and a switch body lb including a threaded boss 2 which protrudes from the tank wall 4. The interlocking assembly 30 includes a switch actuator in the form of a switching boss 12 which is operatively connected to the shaft 3 for a rotation therewith. The switching boss 12 terminates in 15 a bifurcated end defining a transverse slot through a cylindrical wall. An anti-reflex handle 15, shown in Figure 2b, can be mounted within the bifurcated end for actuation of the switch. A limit body in the form of a limit plate 10 is shown in Figure 1. It is mounted 20 for rotation with respect to the switch body lb threaded boss 2. A locking arrangement between the limit plate 10 and switch body lb is also provided. The locking arrangement is operable to lock rotational movement of the limit plate 10 with respect to the switch body lb at a plurality of angularly spaced apart positions. Specifically, the limit plate 10 is lockable in four operator selectable positions using a 25 detent arrangement between the limit plate 10 on the switch body 1b. Referring to Figures 2a, 2b, and 2c and Figures 5a and 5b, it can be seen that the detent arrangement includes a detent member in the form of a selector pin 14c which selectably engages detent recesses 101, 102, 103 and 104 on the limit plate 10. 30 Referring now to Figure 3a, an arm 13 extending from an arm plate 13b is shown. The arm 13 and arm plate 13b has a number of functions. One function is to -6- WO 2008/000022 PCT/AU2007/000881 limit rotation of the shaft 3 for example as is shown progressively in Figures 11a, 11b and 11c. A second function is to indicate the position of the rotary switch 1. A third function is to allow locking of the switch in any one of three positions, 'Earth', 'Off' or 'On' as is shown in Figures 8a, 8b and 8c respectively. 5 Referring to Figure 11b, cooperating first and second clockwise limit stops in the form of a stop pin 11b and a limit stop surface 131 are provided to limit the clockwise angular rotation of the arm 13 with respect to the limit plate 10. In a similar fashion, cooperating first and second anti-clockwise limit stops are provided to limit 10 the anti-clockwise angular rotation of the arm 13 with respect to the limit plate 10. With the embodiment of the invention shown in the drawings, the first anti clockwise limit stop is a stop pin 11a which extends from the limit plate 10 and the second anti-clockwise limit stop is a limit stop surface 132 on the arm 13. 15 The interlock assembly 30 restricts the rotation of a rotary switch 1, or similar switching device, to approximately 135 degrees of rotation. This is illustrated progressively in Figures 3a, 3b and 3c. This enables such switchgear to be rotated to approximately 45 degrees past the target switching position 46, which is 90 degrees past the starting switching position 44. This is necessary for the spring-operated 20 mechanism of such switchgear 1 to be pre-loaded in order for it to switch to the target switch position 46. Importantly, the interlocking assembly 30 does not allow the operator to switch from one position to the next and immediately back to the starting position without 25 having to reposition the device. Components of the rotary switch interlocking assembly 30 are described in more detail as follows: -7- WO 2008/000022 PCT/AU2007/000881 The limit plate 10 provides four operator-selectable positions (as shown in Figure Sa) which consequently allow the operator of the rotary switchgear 1 to perform the following switching operations: (i) switching from the 'Earth' to the 'Off' position (refer to Figures 11a, 11b 5 and 11c); (ii) switching from the 'Off' to the 'On' position (refer to Figures 12a, 12b and 12c); (iii) switching from the 'On' to the 'Off' position (refer to Figures 13a, 13b and 13c); 10 (iv) switching from the 'Off' to the 'Earth' position (refer to Figures 14a, 14b and 14c). The arm plate 13b is securely attached to the switching boss 12. Fasteners 12c, which pass through an arm plate 13b, are used to attach the arm plate 13b to the 15 switching boss 12 thereby ensuring that the arm 13 is fixed with respect to the switching boss 12. In the embodiment of the invention shown, the fasteners 12c are screws, however other attachment means such as rivets or welds may also be used. The spacing indicated by arrows 10a on Figure 6 between the retainer 2a and 20 the rear surface of the switching boss 12 is precisely controlled in order to provide a smooth rotational action by the limit plate 10 which is held between the switching boss 12 and the retainer 2a. Two stop pins 11a and 11b are fastened to the limit plate 10 in the positions 25 shown in Figures 5a and 5b. The stop pins 1a and 11b provide the physical'stop' limitation to the travel of the arm 13 as it is rotated through the approximately 135 degrees of motion by the operator. The stop pins 11a and 11b are effectively 'locked' into the required position by the rod of the selector 14, which fits into the relevant 'slot', referred to as detent recesses 101, 102,103 and 104, in the limit plate 10. 30 - 8- WO 2008/000022 PCT/AU2007/000881 In other embodiments of the invention (not shown) the stop pins 11a and 11b may be fastened to the arm 13. In such an embodiment of the device cooperating stop surfaces would be provided on the limit plate 10. 5 In order to change the angular position of the limit plate 10 the selector assembly 14 is used. There are several main components that make up the selector assembly 14. Referring to Figures 7a and 7b, the selector housing body 14a contains a spring 10 mechanism, which is retained within selector housing body 14a using a selector housing cap 14b, which provides pressure on the selector sliding rod 14d. The selector pin 14c is attached to the selector sliding rod 14d. The selector assembly 14 is attached to the selector support 8. 15 A feature of the selector assembly 14 is that, in its natural state, the spring loaded mechanism ensures that the selector sliding rod 14d pushes the selector pin 14c securely down into the relevant detent recess of the limit plate 10. Another feature of the selector assembly 14 is that if, by chance or by intent, the 20 operator positions the limit plate 10 so that it is between two detent recesses or slots on the limit plate 10, the spring-loaded mechanism of the selector assembly 14 will 'capture' the next detent recess or slot if the operator attempts to rotate the switch shaft 3. Under such a circumstance, the maximum rotation that the operator can undertake is slightly less than 50 degrees, which is much less than the required 25 approximately 135 degrees of motion necessary to 'switch' to the next position. The mounting tag 5 is shown in Figures 4a and 4b. In this embodiment of the device, the mounting tag 5 is an integral part of the 'Off' position locking tag 7. The purpose of the mounting tag 5 is to ensure that the rotary switch interlocking 30 assembly 30 can be properly aligned on the tank wall 4. -9- WO 2008/000022 PCT/AU2007/000881 The base plate 6 is shown in Figures 4a and 4b. The base plate 6 has a hole that suits the profile of the rotary switch's threaded boss 2. The base plate 6 also has three coloured regions 6g, 6r and 6y that, in conjunction with an indicator aperture 13a within the arm plate 13b, facilitate visual identification of the current switch position. 5 In this embodiment of the interlocking assembly 30, the aperture 13a is shaped as an arrow and the 'Earth' position is highlighted using a 'yellow' colour; the 'Off' position is highlighted using a 'green' colour; and the 'On' position is highlighted using a 'red' colour. The mounting tag 5, locking tags 7a, 7b and 7c and selector support 8 are, in this embodiment of the device, attached to the base plate 6. 10 There are three locking tags 7a, 7b and 7c that form a part of the rotary switch interlocking mechanism, and are shown in Figures 4a and 4b. One locking tag is located at each switching position (i.e. at the 'Earth', 'Off' and 'On' positions), as shown in Figures 4a and 4b. The locking tag 7b that is located at the 'Off' position is 15 different to the other two locking tags 7a and 7c located at the 'Earth' and 'On' positions. This is because the locking tag 7b at the 'Off' position also functions as a circuit label holder 9, which provides a durable method of securing a relevant circuit identification label. 20 Each locking tag 7a, 7b and 7c has a slot so that the indicator flag 13 can be padlocked into position. This provides a safety feature. Figures 8a, 8b and 8c show the arm 13 separately locked in the 'Earth' position, locked in the 'Off' position, and locked in the 'On' position by padlocking to the relevant locking tags 7a, 7b and 7c using a padlock 70 25 Both the locking tags 7a and 7c at the 'Earth' and 'On' positions have an additional angled slot. These angled slots 7a" and 7c" are positioned over arcuate slots 71 and 73 within the limit plate 10 shown in Figure 5. The aforementioned slots provide a limit plate locking arrangement whereby an operator can 'lock-out' the 30 'Earth' switching position (i.e. The switch can then only be operated between the 'On' and the 'Off' positions). This feature is shown in Figures 9a and 9b. Similarly, -10- WO 2008/000022 PCT/AU2007/000881 an operator can 'lock-out' the 'On' switching position (i.e. the switch can then only be operated between the 'Off' and the 'Earth' positions). This feature is shown in Figures 10a and 10b. 5 In this embodiment of the interlocking assembly 30 a circuit label holder 9 is an integral part of the 'Off' locking tag 7b, which is shown in Figures 4a and 4b. The circuit label holder 9 is provided so that a label can be easily and securely attached to the interlocking assembly 30 for the purpose of identifying the circuit that is switched by the rotary switch 1. The label is placed under a clear polycarbonate (or 10 any other similar transparent material) cover which is, in turn, fastened to the locking tag 7b using two 'Wing Nuts'. Operation of the interlocking assembly 30 will now be described. 15 Referring to Figures 11a, 11b and 11c, it can be seen that the interlocking assembly 30 provides a rotational mechanism where the rotary switch 1, if initially in the 'Earth' position, can be rotated to the target'Off' position in one movement. This action is performed by the operator first rotating the limit plate 10 so that the selector pin 14c of the selector 14 is in the 'Earth->Off' position (ie. so that the 20 selector pin 14c is captured by detent recess 102 of the limit plate 10 shown in Figure 5a) and then using the 'anti-reflex' operating handle 15 to rotate the coupled switching boss 12 and arm 13 to approximately 45 degrees past the 'Off' position in order for the spring-loaded mechanism of the rotary switch 1 to 'trigger' into the 'Off' position. The operator then 'relaxes' the torque from the 'anti-reflex' operating 25 handle 15, thereby allowing the arm 13 and switching boss 12 to finally settle into the 'Off' position. Referring to Figure 12a, 12b and 12c, it can be seen that the interlocking assembly 30 also provides a rotational mechanism where the rotary switch 1, if 30 initially in the 'Off' position, can be rotated to the target 'On' position in one movement. This action is performed by the operator first rotating the limit plate 10 so - 11 - WO 2008/000022 PCT/AU2007/000881 that the selector pin 14c of the selector 14 is in the 'Off-+On' position (ie. so that the selector pin 14c is captured by detent recess 104 of the limit plate 10 shown in Figure 5a) and then using the 'anti-reflex' operating handle 15 to rotate the coupled switching boss 12 and arm 13 to approximately 45 degrees past the 'On' position in 5 order for the spring-loaded mechanism of the rotary switch 1 to 'trigger' into the 'On' position. The operator then 'relaxes' the torque from the 'anti-reflex' operating handle 15, thereby allowing the arm 13 and switching boss 12 to finally settle into the 'On' position. 10 Referring to Figures 13a, 13b and 13c, it can be seen that the interlocking assembly 30 also provides a rotational mechanism where the rotary switch 1, if initially in the 'On' position, can be rotated to the target 'Off' position in one movement. This action is performed by the operator first rotating the limit plate 10 so that the selector pin 14c of the selector 14 is in the 'On->Off' position (ie. so that the 15 selector pin 14c is captured by detent recess 103 of the limit plate 10 shown in Figure 5a) and then using the 'anti-reflex' operating handle 15 to rotate the coupled switching boss 12 and arm 13 to approximately 45 degrees past the 'Off' position in order for the spring-loaded mechanism of the rotary switch 1 to 'trigger' into the 'Off' position. The operator then 'relaxes' the torque from the 'anti-reflex' operating 20 handle 15, thereby allowing the arm 13 and switching boss 12 to finally settle into the 'Off' position. Referring to Figures 14a, 14b and 14c, it can be seen that the interlocking assembly 30 also provides a rotational mechanism where the rotary switch 1, if 25 initially in the 'Off' position, can be rotated to the target 'Earth' position in one movement. This action is performed by the operator first rotating the limit plate 10 so that the selector pin 14c of the selector 14 is in the 'Off-->Earth' position (ie. so that the selector pin 14c is captured by detent recess 101 of the limit plate 10 shown in Figure 5a) and then using the 'anti-reflex' operating handle 15 to rotate the coupled 30 switching boss 12 and arm 13 to approximately 45 degrees past the 'Earth' position in order for the spring-loaded mechanism of the rotary switch 1 to 'trigger' into the -12- WO 2008/000022 PCT/AU2007/000881 'Earth' position. The operator then 'relaxes' the torque from the 'anti-reflex' operating handle 15, thereby allowing the arm 13 and switching boss 12 to finally settle into the 'Earth' position. 5 An important safety feature of the device is that it requires the operator to reposition the limit plate 10 to the 'Earth-+Off' position in order to be able to switch back to the 'Earth' position. This prevents, for example, the operator from switching a 'live' electrical cable to the 'Earth' position (thus creating a 'faulted' situation) and then immediately switching back to the 'Off' position (thus creating an electric arc 10 under oil). If the energy of the electrical arc is of sufficient magnitude then the rotary switch is unlikely to successfully 'break' the arc thereby creating a potentially dangerous (ie. explosive) situation. The device effectively prevents this from occurring since the operator must reposition the limit plate 10 following a switching operation. This introduces a critical delay-time which gives the upstream network 15 protection the opportunity of clearing the electric fault before further switching is attempted by the operator. While the present invention has been described in terms of a preferred embodiment in order to facilitate better understanding of the invention, it should be 20 appreciated that various modifications can be made without departing from the principles of the invention. Therefore, the invention should be understood to include all such modifications within its scope. -13 -

Claims (18)

1. A rotary switch interlocking assembly mountable to a multi-position rotary switch having a shaft and a switch body, the interlocking assembly including: a switch actuator operatively connected to the shaft for rotation therewith 5 about a switch axis; a limit body mounted for rotation with respect to the switch body; a locking arrangement between the limit body and the switch body, the locking arrangement operable to lock rotational movement of the limit body with respect to the switch body at a plurality of angularly spaced apart positions; 10 cooperating first and second clockwise limit stops, the first clockwise limit stop rotating with the shaft and the second clockwise limit stop mounted to or integral with the limit body, the first and second clockwise limit stops arranged to limit the clockwise angular rotation of the shaft with respect to the limit body; and cooperating first and second anticlockwise limit stops, the second 15 anticlockwise limit stop rotating with the shaft and the first anticlockwise limit stop mounted to or integral with the limit body, the first and second anticlockwise limit stops arranged to limit the anticlockwise angular rotation of the shaft with respect to the limit body; whereby when the limit body is locked in any one of the plurality of 20 circumferentially spaced apart positions, the limit stops limit rotation of the rotary switch shaft to a particular angular range.

2. An assembly as claimed in claim 1 wherein the particular angular range is such that an operator can only switch between two switch positions while the limit 25 body is locked in any one of its plurality of circumferentially spaced apart positions.

3. An assembly as claimed in claim 2 wherein the particular angular range is between 120 and 150 degrees. 30

4. An assembly as claimed in claim 3 wherein the particular angular range is between 125 and 145 degrees. -14 - WO 2008/000022 PCT/AU2007/000881

5. An assembly as claimed in claim 4 wherein the particular angular range is between 130 and 140 degrees.

6. An assembly as claimed in claim 2 wherein the switch actuator is a boss. 5

7. An assembly as claimed in claim 6 wherein the boss terminates in a bifurcated end defining a transverse slot through a cylindrical wall, whereby an anti-reflex handle can be mounted within the bifurcated end for actuation of the switch. 10

8. An assembly as claimed in claim 1 wherein the locking arrangement includes an arm operatively connected to the shaft or the switch actuator for rotational movement therewith. 15

9. An assembly as claimed in claim 8 wherein the arm has a first limit stop surface and a second limit stop surface, the first and second limit stop surfaces spaced apart from each other, whereby the first and second limit stop surfaces form the first clockwise limit stop and the second anticlockwise limit stop respectively. 20

10. An assembly as claimed in claim 9 wherein the limit body supports a first stop pin and a second stop pin, the first and second stop pins spaced apart from each other, whereby the first and second limit stop pins form the first anticlockwise limit stop and the second clockwise limit stop respectively. 25

11. An assembly as claimed in claim 10 wherein the limit body is a limit plate.

12. An assembly as claimed in claim 11 wherein the locking arrangement includes a detent arrangement. 30

13. An assembly as claimed in claim 12 wherein the detent arrangement includes a detent member mounted to prevent circumferential movement while -15 - WO 2008/000022 PCT/AU2007/000881 allowing movement in a radial direction with respect to the switch axis and a plurality of spaced apart notches within a arcuate edge on the limit plate, the notches arranged to selectively receive the detent member so as to lock movement of the limit plate with respect to the detent member against circumferential movement about the 5 switch axis.

14. An assembly as claimed in claim 13 wherein the detent arrangement includes a detent spring, the spring biasing the detent member into engagement with the notches, 10 wherein the detent member is manually movable so as to hold it out of any of the notches thereby allowing manual rotation of the limit plate with respect to the switch body.

15. An assembly as claimed in claim 14 wherein the arcuate edge is concave 15 and the spring biases the detent member radially outwards with respect to the switch axis.

16. An assembly as claimed in claim 15 further including a limit plate locking arrangement, the limit plate locking arrangement allowing for locking the limit plate 20 such that it can only be rotated between two of three positions.

17. An assembly as claimed in claim 16 wherein the limit plate locking arrangement includes an arcuate groove or slot within the locking plate and a padlock shackle, the shackle lockable to a tab mounted to the switch body. 25

18. A rotary switch interlocking assembly substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings. -16-