referring to the drawings in detail , an adaptor unit of a plug - in type in accordance with the invention is identified generally therein by the numeral 10 . unit 10 comprises an insulating housing 12 including a reverse face 14 , a cover 16 comprising side walls 18 , and obverse face 20 , top wall 22 and bottom wall 24 . a longitudinal axis 26 extends between top wall 22 and bottom wall 24 , and a transfer axis 28 extends between reverse face 14 and obverse face 20 . a plurality of prongs 32 extends rearwardly from reverse face 14 , configured to engage in a standard receptacle outlet ( not shown ), which prongs terminate within housing 12 in a line terminal 34 and a return line terminal 36 , and the ground terminal 38 . the line terminal 34 and return line terminal 36 are carried on an insulating switch block 40 disposed within housing 12 . a dummy ground prong 42 projects rearwardly from the base 14 , positioned to engage in a lower ground socket opening of a duplex receptacle outlet ( not shown ) when prongs 32 engage in an upper outlet thereof , so as to physically stabilize interconnection between the duplex receptacle and adaptor unit 10 . housing 12 is provided on obverse face 20 thereof with three pluralities of groups of openings 44a , 44b , 44c , each of which plurality is configured as a standard convenience outlet . a prong electrode assembly 50 underlays openings 44a - 44c , which assembly comprises an insulating holder 52 having three axially aligned channels 54 , 56 , 58 therein , within which there is respectively located a line strip electrode 64 , a return line strip electrode 66 , and a ground strip electrode 68 . assembly 50 is rigidly supported within housing 12 by a spacer 70 adjacent bottom wall 24 , while the upper end of holder 52 bears upon insulating switch block 40 , whereby strips 64 , 66 , 68 underlay the respective prong openings of groups 44a , 44b , 44c a circuit board 72 underlays holder 52 . strip electrodes 64 , 66 and 68 are each provided with a leg formed unitarily therewith , which legs are respectively identified by the numerals 74 , 76 , 78 , with legs 74 , 76 being connected to circuit board 72 , and leg 78 to ground terminal 38 , in electrically conducting relationship . a first pair of leaf springs 80 are respectively supported from line terminal 34 and return line terminal 36 in upstanding relationship ; a second pair of leaf springs are 82 supported from circuit board 72 in opposed spaced apart relationship with the first pair of springs , the second pair of springs being respectively connected to line strip electrode 64 and return line strip electrode 66 by conductors 86 on circuit board 72 . a contact 86 is disposed adjacent the distal end of each leaf spring of the pairs of leaf springs 80 , 82 which contacts in the relaxed condition of the leaf springs are normally open . switch block 40 is provided with a track 88 therein axially aligned with the transverse axis 28 . an actuator 90 is mounted for sliding movement along track 88 between first and second positions . actuator 90 includes a pair of shoulders 92 which respectively project on opposed lateral sides of switch block 40 , which shoulders are disposed rearwardly of the first pair of leaf springs 80 , whereby when the actuator is moved to its first position against the bias of leaf springs 80 , the first pair of leaf springs will be urged towards the second pair of leaf springs 82 , and close contacts 86 , thereby interconnecting line terminal 34 with line strip electrode 64 , and return line terminal 36 with return line strip electrode 66 . when actuator 90 is released from its first position , it will move under the influence of leaf springs 80 to its second position . actuator 90 is moved to its first position by a conditioner 94 which is mounted from switch block 40 for sliding movement parallel to the travel of actuator 90 between a first position and a second position , with coil springs 96 biasing the conditioner to its first position . a latch plate 98 is hinged to actuator 90 by ears 100 which are received in recesses 102 provided in actuator 90 . conditioner 94 comprises a tab portion 104 which underlays latch plate 98 , and a spring 96 biases the latch plate towards the tab portion . the tab portion 104 is provided with a hook 108 adjacent its distal end , and the latch plate 98 is provided with an opening 110 therein . the switching action of the assembly as thus far described can best be appreciated from a consideration of fig6 a - 6d . as seen in fig6 a , conditioner 94 is biased to its first ( forward ) position by spring 96 , actuator 90 is biased to its second position by leaf spring 80 , and latch plate 98 is biased towards the tab portion 104 of the conditioner . as seen in fig6 b , a manual pressure applied to conditioner 94 urges the conditioner to its second position , causing hook 108 to latch into opening 110 . as seen in fig6 c , the release of manual pressure from conditioner 94 causes the conditioner to revert to its first position under the influence of spring 96 , and entrain actuator 90 to its first position , thereby closing contact 86 . a solenoid 112 is mounted to switch block 40 , operatively connected to circuit board 72 . solenoid 112 has a plunger 114 which is biased inwardly , with excitation of the solenoid serving to move the plunger outwardly . as best seen in fig6 d , the outward movement of plunger 114 brings it into contact with latch plate 98 , to urge the latch plate against the bias of spring 106 , thereby causing the latch plate to unlatch from conditioner 94 , and permit the return of actuator 90 to its second position and so open contacts 86 . latch plate 98 may be tripped manually should this be desired by means of a trip finger 116 , the action of which is illustrated in fig7 a and 7b . housing 12 includes in obverse face 20 a window opening 118 therethrough to provide access to conditioner 94 for the actuation thereof . it will be appreciated that the state of contacts 86 , i . e . whether closed or open , cannot be predicted from the state of conditioner 94 . conveniently , a switch indicator 120 is mounted to actuator 90 to project forwardly therefrom through opening 122 in the obverse face of housing 16 , to provide a visual indication of the state of the switch contacts 86 . circuit board 72 will normally include circuit means ( not shown ) as is generally known in the art for detecting a trip condition and providing a trip output suitable for the actuation of solenoid 112 responsive to an input signal from a transducer ( not shown ) or from an otherwise detected condition , for example a ground fault condition , such as is disclosed in u . s . patent . unit 10 as illustrated is particularly adapted for use in the ground fault application by the provision of a test switch 124 , which serves to simulate ground fault , and an indicator lamp 126 , which provides a visual indication of the presence of an operational line voltage across the line and return line electrodes 64 , 66 . conveniently , test switch 124 and lamp 126 are mounted from a subsidiary circuit board 128 . it will be understood that adaptor unit 10 may be easily modified whereby actuator 90 serves to set contact 84 to an open condition when at second position , or to set one pair of contacts open and one pair closed , for example , and that further pairs of contacts may be provided should it be desired to increase the number of switching circuits . many other obvious changes to the illustrative embodiments may be made , and it is intended that these fall within the scope of the invention that is claimed .