[ 0025 ] fig1 shows a circuit breaker 20 . circuit breaker 20 generally includes a molded case having a top cover 22 attached to a mid cover 24 coupled to a base 26 . [ 0026 ] fig2 shows an exploded diagram of circuit breaker 20 , showing the internal construction thereof . an opening 28 , formed generally centrally within top cover 22 , is positioned to mate with a corresponding mid cover opening 30 , which is accordingly aligned with opening 28 when mid cover 24 and top cover 22 are coupled to one another . electronic trip unit 23 is removably positioned within top cover 22 as shown . in a 3 - pole system ( i . e ., corresponding with three phases of current ), three rotary cassettes 32 , 34 and 36 are disposed within base 26 . cassettes 32 , 34 and 36 are commonly operated by an interface between an operating mechanism 38 via a cross pin 40 . operating mechanism 38 is positioned and configured atop cassette 34 , which is generally disposed intermediate to cassettes 32 and 36 . operating mechanism 38 operates substantially as described herein and as described in u . s . pat . no . 6 , 087 , 913 entitled “ circuit breaker mechanism for a rotary contact assembly ”. an operating handle 44 extends through openings 28 and 30 and allows for external operation of cassettes 32 , 34 and 36 . examples of rotary contact structures that may be operated by operating mechanism 38 are described in more detail in u . s . pat . nos . 6 , 114 , 641 and 09 / 384 , 908 ( ge docket number 41pr7613 / 7619 ), both entitled “ rotary contact assembly for high - ampere rated circuit breakers ”, and u . s . pat . no . 6 , 175 , 288 entitled “ supplemental trip unit for rotary circuit interrupters ”. cassettes 32 , 34 , 36 are typically formed of high strength plastic material and each include opposing sidewalls 46 , 48 . sidewalls 46 , 48 have an arcuate slot 52 positioned and configured to receive and allow the motion of cross pins 40 by action of operating mechanism 38 . referring now to fig3 , and 5 , an exemplary rotary contact assembly 56 that is disposed within each cassette 32 , 34 , 36 is shown in the “ off ”, “ on ” and “ tripped ” conditions , respectively . also depicted are partial side views of operating mechanism 38 , the components of which are described in greater detail further herein . rotary contact assembly 56 includes a load side contact strap 58 and line side contact strap 62 for connection to a power source and a protected circuit ( not shown ), respectively . load side contact strap 58 includes a stationary contact 64 and line side contact strap 62 includes a stationary contact 66 . rotary contact assembly 56 further includes a movable contact arm 68 having a set of contacts 72 and 74 that mate with stationary contacts 64 and 66 , respectively . in the “ off ” position ( fig3 ) of operating mechanism 38 , wherein operating handle 44 is oriented to the left ( e . g ., via a manual or mechanical force ), contacts 72 and 74 are separated from stationary contacts 64 and 66 , thereby preventing current from flowing through contact arm 68 . it should be appreciated that while rotary contact assembly 56 shows a contact arm having a pair of movable contacts , rotary contact assemblies wherein the contact arm has only a single movable contact is contemplated . in the “ on ” position of operating mechanism 38 shown in fig4 wherein operating handle 44 is oriented to the right as depicted in fig4 ( e . g ., via a manual or mechanical force ), contacts 72 and 74 are mated with stationary contacts 64 and 66 , thereby allowing current to flow through contact arm 68 . in the “ tripped ” position shown in fig5 operating handle 44 is oriented between the “ on ” position and the “ off ” positions ( typically by the release of mechanism springs within operating mechanism 38 , described in greater detail herein ). in this “ tripped ” position , contacts 72 and 74 are separated from stationary contacts 64 and 66 by the action of operating mechanism 38 , thereby preventing current from flowing through contact arm 68 . after operating mechanism 38 is in the “ tripped ” position , it must ultimately be returned to the “ on ” position for operation . this is effectuated by applying a reset force to move operating handle 44 to a “ reset ” condition , which is beyond the “ off ” position ( i . e ., further to the left of the “ off ” position in fig3 ), and then back to the “ on ” position . this reset force must be high enough to overcome the mechanism springs , described herein . contact arm 68 is mounted on a rotor structure 76 that houses one or more sets of contact springs . contact arm 68 and rotor structure 76 pivot about a common center 78 . cross pin 40 interfaces through an opening 82 within rotor structure 76 generally to cause contact arm 68 to be moved from the “ on ”, “ off ” and “ tripped ” position . referring now to fig6 - 8 , the components of operating mechanism 38 will now be detailed . as viewed in fig6 - 8 , operating mechanism 38 is in the “ tripped ” position . operating mechanism 38 has operating mechanism side frames 86 configured and positioned to straddle sidewalls 46 , 48 of cassette 34 ( fig2 ). operating handle 44 ( fig2 - 4 ) is rigidly interconnected with a drive member or handle yoke 88 . handle yoke 88 includes opposing side portions 89 . each side portion 89 includes an extension 91 at the top of side portion 89 , and a u - shaped portion 92 at the bottom portion of each side portion 89 . u - shaped portions 92 are rotatably positioned on a pair of bearing portions 94 protruding outwardly from side frames 86 . bearing portions 94 are configured to retain handle yoke 88 , for example , with a securement washer . handle yoke 88 further includes a roller pin 114 extending between extensions 91 . handle yoke 88 is connected to a set of powerful mechanism springs 96 by a spring anchor 98 , which is generally supported within a pair of openings 102 in handle yoke 88 and arranged through a complementary set of openings 104 on the top portion of mechanism springs 96 . referring to fig9 the bottom portion of mechanism springs 96 include a pair of openings 206 . a drive connector 201235 operatively couples mechanism springs 96 to other operating mechanism components . drive connector 201235 comprises a pin 202 disposed through openings 206 , a set of side tubes 203 arranged on pin 202 adjacent to the outside surface of the bottom portion of mechanism springs 96 , and a central tube 204 arranged on pin 202 between the inside surfaces of the bottom portions of mechanism springs 96 . central tube 204 includes step portions at each end , generally configured to maintain a suitable distance between mechanism springs 96 . while drive connector 201235 is detailed herein as tubes 203 , 204 and a pin 202 , any means to connect the springs to the mechanism components are contemplated . referring to fig8 , and 11 , a pair of cradles 106 are disposed adjacent to side frames 86 and pivot on a pin 108 disposed through an opening 112 approximately at the end of each cradle 106 . each cradle 106 includes an edge surface 107 , an arm 122 depending downwardly , and a cradle latch surface 164 above arm 122 . edge surface 107 is positioned generally at the portion of cradle 106 in the range of contact with roller pin 114 . each cradle 106 also includes a stop surface 110 formed thereon . a rivet 116 disposed through an arcuate slot 118 within each side frame 86 , as best seen in fig5 and 8 , guides the movement of each cradle 106 . rivets 116 are disposed within an opening 117 on each cradle 106 ( fig1 ). an arcuate slot 168 is positioned intermediate to opening 112 and opening 117 on each cradle 106 . an opening 172 is positioned above slot 168 . referring back to fig6 - 8 , a primary latch 126 is positioned within side frames 86 . primary latch 126 includes a pair of side portions 128 ( fig8 ). each side portion 128 includes a bent leg 124 at the lower portion thereof . side portions 128 are interconnected by a central portion 132 . a set of extensions 166 depend outwardly from central portion 132 positioned to align with cradle latch surfaces 164 . side portions 128 each include an opening 134 positioned so that primary latch 126 is rotatably disposed on a pin 136 . pin 136 is secured to each side frame 86 . a set of upper side portions 156 are defined at the top end of side portions 128 . each upper side portion 156 has a primary latch surface 158 . a secondary latch 138 is pivotally straddled over side frames 86 . secondary latch 138 includes a set of pins 142 disposed in a complementary pair of notches 144 on each side frame 86 . secondary latch 138 includes legs 139 each having a secondary latch trip tab 146 that extends perpendicularly from operating mechanism 38 . secondary latch 138 includes a set of latch surfaces 162 , that align with primary latch surfaces 158 . secondary latch 138 is biased in the clockwise direction due to the pulling forces of a spring 148 ( fig8 ). spring 148 has a first end connected at an opening 152 upon secondary latch 138 , and a second end connected at a frame cross pin 154 disposed between frames 86 . a set of upper links 174 are connected to cradles 106 . upper links 174 generally have a right angle shape , as best viewed in fig8 and 10 . legs 175 ( in a substantially horizontal configuration in fig1 ) of upper links 174 each have a cam surface 171 that interfaces a roller 173 disposed between frames 86 ( fig8 ). legs 176 ( in a substantially vertical configuration in fig8 and 10 ) of upper links 174 each have a pair of openings 182 , 184 and a u - shaped portion 186 at the bottom end thereof . opening 184 is intermediate to opening 182 and u - shaped portion 186 . upper links 174 connect to cradle 106 via a securement structure such as a rivet pin 188 disposed through opening 172 and opening 182 , and a securement structure such as a rivet pin 191 disposed through slot 168 and opening 184 . rivet pins 188 , 191 ( fig1 ) both attach to a connector 193 to secure each upper link 174 to each cradle 106 . each pin 188 , 191 includes raised portions 189 , 192 , respectively . raised portions 189 , 192 are provided to maintain a space between each upper link 174 and each cradle 106 . the space serves to reduce or eliminate friction between upper link 174 and cradle 106 during any operating mechanism motion , and also to spread force loading between cradles 106 and upper links 174 . upper links 174 are each interconnected with a lower link 194 . referring now to fig8 and 9 , u - shaped portion 186 of each upper link 174 is disposed in a complementary set of bearing washers 196 . bearing washers 196 are arranged on each side tube 203 . bearing washers 196 are configured to include side walls spaced apart sufficiently so that u - shaped portions 186 of upper links 174 fit in bearing washer 196 . pin 202 is disposed through side tubes 203 and central tube 204 . pin 202 interfaces upper links 174 and lower links 194 via side tubes 203 . therefore , each side tube 203 is a common interface point for upper link 174 ( as pivotally seated within side walls of bearing washer 196 ), lower link 194 and mechanism springs 96 . each lower link 194 is interconnected with a crank 208 via a pivotal rivet 210 . each crank 208 pivots about a center 211 . crank 208 has an opening 212 where cross pin 40 ( fig2 ) passes through into arcuate slot 52 of cassettes 32 , 34 and 36 and a complementary set of arcuate slots 214 on each side frame 86 ( fig8 ). a spacer 234 is included on each pivotal rivet 210 between each lower link 194 and crank 208 . spacers 234 spread the force loading from lower links 194 to cranks 208 over a wider base , and also reduces friction between lower links 194 and cranks 208 , thereby minimizing the likelihood of binding ( e . g ., when operating mechanism 38 is changed from the “ off ” position to the “ on ” position manually or mechanically , or when operating mechanism 38 is changed from the “ on ” position to the “ tripped ” position of the release of primary latch 126 and secondary latch 138 ). referring back to fig3 - 5 , the movement of operating mechanism 38 relative to rotary contact assembly 56 will be detailed . referring to fig3 in the “ off ” position operating handle 44 is rotated to the left and mechanism springs 96 , lower link 194 and crank 208 are positioned to maintain contact arm 68 so that movable contacts 72 , 74 remain separated from stationary contacts 64 , 66 . operating mechanism 38 becomes set in the “ off ” position after a reset force properly aligns primary latch 126 , secondary latch 138 and cradle 106 ( e . g ., after operating mechanism 38 has been tripped ) and is released . thus , when the reset force is released , extensions 166 of primary latch 126 rest upon cradle latch surfaces 164 , and primary latch surfaces 158 rest upon secondary latch surfaces 162 . each upper link 174 and lower link 194 are bent with respect to each side tube 203 . the line of forces generated by mechanism springs 96 ( i . e ., between spring anchor 98 and pin 202 ) is to the left of bearing portion 94 ( as oriented in fig3 - 5 ). cam surface 171 of upper link 174 is out of contact with roller 173 . referring now to fig4 a manual closing force was applied to operating handle 44 to move it from the “ off ” position ( i . e ., fig4 ) to the “ on ” position ( i . e ., to the right as oriented in fig5 ). while the closing force is applied , upper links 174 rotate within arcuate slots 168 of cradles 106 about pins 188 , and lower link 194 is driven to the right under bias of the mechanism spring 96 . side walls of bearing washers 196 maintain the position of upper link 174 on side tube 203 and minimize likelihood of binding ( e . g ., so as to prevent upper link 174 from shifting into springs 96 or into lower link 194 ). to align vertical leg 176 and lower link 194 , the line of force generated by mechanism springs 96 is shifted to the right of bearing portion 94 , which causes rivet 210 coupling lower link 194 and crank 208 to be driven downwardly and to rotate crank 208 clockwise about center 211 . this , in turn , drives cross pin 40 to the upper end of arcuate slot 214 . therefore , the forces transmitted through cross pin 40 to rotary contact assembly 56 via opening 82 drive movable contacts 72 , 74 into stationary contacts 64 , 66 . the interface between primary latch 126 and secondary latch 138 ( i . e ., between primary latch surface 158 and secondary latch surface 162 ), and between cradles 106 and primary latch 126 ( i . e ., between extensions 166 and cradle latch surfaces 164 ) is not affected when a force is applied to operating handle 44 to change from the “ off ” position to the “ on ” position . referring again to fig5 in the “ tripped ” condition , secondary latch trip tab 146 has been displaced , e . g ., by electronic trip unit interlock , described in detail below , and the interface between primary latch 126 and secondary latch 138 is released . extensions 166 of primary latch 126 are disengaged from cradle latch surfaces 164 , and cradles 106 is rotated clockwise about pin 108 ( i . e ., motion guided by rivet 116 in arcuate slot 118 ). the movement of cradle 106 transmits a force via rivets 188 , 191 to upper link 174 having cam surface 171 . after a short predetermined rotation , cam surface 171 of upper link 174 contacts roller 173 . the force resulting from the contact of cam surface 171 on roller 173 causes upper link 174 and lower link 194 to buckle and allows mechanism springs 96 to pull lower link 194 via pin 202 . in turn , lower link 194 transmits a force to crank 208 ( i . e ., via rivet 210 ) causing crank 208 to rotate counter clockwise about center 211 and drive cross pin 40 to the lower portion of arcuate slot 214 . the forces transmitted through cross pin 40 to rotary contact assembly 56 via opening 82 cause movable contacts 72 , 74 to separate from stationary contacts 64 , 66 . referring now to fig1 - 18 , the electronic trip unit interlock mechanism will be described in detail . fig1 and 13 show isometric views of circuit breaker 20 rotated approximately 180 degrees about a central axis relative to fig1 . fig1 shows the components of the electronic trip unit interlock are separated from the operating mechanism and fig1 shows the components installed . in each of fig1 and 13 , the top cover 22 , mid cover 24 , and base 26 removed and the outside cassette 36 is not shown for clarity . the trip arm 253 is mounted to the side of operating mechanism 38 as shown and rotates about a fixed pivot 254 . trip arm 253 includes a leg 257 having a first surface in contact with trip plunger 275 and an extension 270 having a latch surface for contacting secondary trip latch 138 . extension bar 255 is positioned between operating mechanism 38 and breaker load vent assembly 267 . extension bar includes a finger 259 having a first surface that comes into contact with electronic trip unit 23 when it is installed , and a nub 258 having a second surface in contact with trip plunger 275 . center barrier 268 contains a bored hole 271 located as shown . trip spring 274 and trip plunger 275 are positioned within hole 271 . fig1 shows the trip plunger 275 positioned under leg 257 of trip arm 253 . [ 0052 ] fig1 shows extension bar 255 as it interacts with trip plunger 275 . when extension bar 255 is in the position shown , it holds trip plunger 275 in its depressed position away from leg 257 of trip arm 253 . when extension bar 255 is allowed to move , to the position shown in phantom in fig1 , it allows trip plunger 275 to be driven in an upwards direction by trip spring 274 into an interference with leg 257 of trip lever 253 . extension bar 255 is held in the position which depresses trip plunger 275 when the electronic trip unit 23 is installed in circuit breaker 20 as shown in fig1 . when electronic trip unit 23 is removed , extension bar 255 is released , allowing trip plunger 275 to move in an upwards direction , moving extension bar 255 to the phantom position shown in fig1 . [ 0053 ] fig1 clarifies the relationship between finger 259 of extension bar 255 as it relates to mid cover 24 and electronic trip unit 23 . fig1 shows a detail of a portion 217 of fig1 , showing finger 259 extending up from mid cover 24 . referring now to fig1 , in response to electronic trip unit 23 being removed , spring 274 has urged plunger 275 in an upward direction , causing extension bar 255 to move up and trip arm 253 to rotate in a counter - clockwise direction about pivot 254 . extension 270 of trip arm 253 includes a latch surface that interacts with secondary latch trip tab 146 of secondary latch 138 . in response to this interaction , secondary latch 138 is caused to rotate in a clockwise direction about pins 142 , causing the operating mechanism to trip as previously described , separating movable contacts 74 , 72 from fixed contacts 66 , 64 . unless electronic trip unit 23 is replaced , the operating mechanism will remain in this position and will not allow the main contacts to be closed . when trip unit 23 is replaced as shown in fig1 , surface 260 interacts with finger 259 of extension bar 255 , forcing extension bar 255 to rotate downwardly . when extension bar is forced down , nub 258 forces plunger 275 to become depressed , as shown in fig1 . in response to plunger 275 being depressed , trip arm 253 is permitted to rotate clockwise about pivot 254 . spring 265 ( fig1 , 18 ) urges trip arm 253 to rotate in a clockwise direction , thus causing trip arm 253 to rotate in a clockwise direction when free to do so . while the invention has been described with reference to a preferred embodiment , it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention . for example , trip arm 253 may be mounted and configured to slide instead of rotate , and / or may engage an intermediary which then actuates secondary trip latch 138 , rather than actuating secondary trip latch 138 directly . additionally , electronic trip unit 23 may engage a surface of trip arm 253 or other intermediary rather than work directly against plunger 275 . these and other modifications would occur to the skilled artisan to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof . therefore , it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention , but that the invention will include all embodiments falling within the scope of the appended claims .