in the description below , only one circuit breaker pole is described , it being understood that the invention applies to a three - phase circuit breaker having three identical poles . the circuit breaker pole described is of the bare type , but the invention naturally also applies to circuit breakers within grounded metal cladding . in fig1 reference 1 designates an enclosure , e . g . made of ceramic , filled with a gas having good dielectric properties , such as sulfur hexafluoride sf 6 . the interrupter chamber includes a fixed assembly comprising a fixed metal cylinder 2 connected to a first current terminal ( not shown ). a &# 34 ; closure &# 34 ; resistor 3 is disposed axially in the enclosure 1 ; it is constituted by a stack of disks 3a surrounded by an insulating side sheath 4 ; a first end of the stack is connected to the above - mentioned first current terminal ; the other end of the stack is terminated by a metal end plate 6 . a metal tube 7 is fixed to the metal cylinder 2 and constitutes the fixed main contact of the circuit breaker ; metal arms 8 serve to fix a metal tubular portion 9 to the same cylinder 2 , with the end 9a of the tubular portion being made of an alloy that withstands the effects of electric arcing . this tubular portion 9 - 9a constitutes the fixed arcing contact of the circuit breaker . a metal piece 11 is fixed to the end plate 6 , preferably by means of screws 10 , with the piece 11 carrying metal arms 12 parallel to the axis of the enclosure ; there are preferably two such arms ; a metal ring 13 is welded to the ends of these arms and constitutes a fixed electrode for inserting the resistor 3 during closure . the moving assembly of the circuit breaker comprises a circular metal end plate 15 disposed perpendicularly to the axis of the enclosure . this metal end plate 15 carries a ring of contact fingers 16 constituting the moving main contacts which co - operate with the tube 7 . the fingers 16 are protected by an anticorona cap 16a . the side of the end plate 15 facing away from the contacts 16 is connected to two cylinders that are coaxial about the axis of the enclosure . these cylinders , referenced as 17 and 18 define a blast volume v1 in which a fixed blast piston is disposed ( not shown ). one of the cylinders , e . g ., the inner cylinder 17 , is mechanically connected to a drive rod ( not shown ); the other cylinder , 18 , is electrically connected by sliding contacts ( not shown ) to a second current terminal ( not shown ). the inner cylinder 17 is extended through the end plate 15 by a cylindrical portion 17a provided on the inside with sliding contacts 17b . a cylindrical portion 20 secured to the end plate 15 is disposed coaxially around the cylindrical portion 17a . the cylindrical portions 17a and 20 together define an annular volume v2 in which there moves the end of a blast nozzle 22 made of insulating material . as in conventional circuit breaker nozzles , the nozzle 22 has a throat 22a , however it is terminated by a ring 22b which constitutes a shoulder facilitating sliding thereof in the volume v2 . a spring 24 bears firstly against the shoulder 22b and secondly on a shoulder 20a at the end of the cylindrical portion 20 . the nozzle 22 is connected by a ring 26 to a metal tubular portion 30 constituting a semi - moving arcing contact co - operating with the fixed arcing contact 9 - 9a . the portion 30 is terminated at one end by a contact piece 30a made of an alloy that withstands the effects of electric arcing . it may be observed that the end plate 15 includes passages 15a to allow the blast gas to pass from the volume v1 to the volume v2 during an opening operation . under normal operating conditions , the circuit breaker is in the configuration shown in fig1 . the permanent current passes via the first current contact , the cylinder 2 , the tube 7 , the fingers 16 , the end plate 15 , the tube 18 , and the second current terminal . the circuit breaker is triggered by moving its moving assembly under drive from the circuit breaker control means ( not shown ) directed towards the right of fig1 . in a first stage , as shown in fig2 the moving assembly is moved a few tens of millimeters to the right . by inertia , and also because of the increase in the pressure in the volume v2 behind the ring 22b , due to the gas in the volume v1 being compressed , the semi - moving subassembly constituted by the nozzle 22 and the arcing contact 30 - 30a remains in the position it occupies in the configuration of fig1 . this enables the main contacts 7 and 16 to separate , with the current then switching to flow through the arcing contacts 9 - 9a and 30 - 30a . during this movement , the spring 24 is compressed . after the moving equipment has moved further , the contacts 16 have gone past the insertion electrode 13 and the arcing contacts 9 - 9a and 30 - 30a are on the point of separating ( see fig3 ) since , with the spring being fully compressed , the arcing contact 30 - 30a of the semi - moving subassembly is being driven by the moving assembly . after the arcing contacts have separated ( fig4 ) an arc is struck between these contacts , but it is rapidly extinguished by energetic blasting through the nozzle 22 . the pressure in the volume v2 falls off rapidly and , under the effect of the spring , the semi - moving subassembly constituted by the nozzle 22 and the arcing contact 30 - 30a returns to its initial position relative to the moving assembly . at the end of the opening maneuver , the circuit breaker is in its open position as shown in fig5 . the voltage is held between the ends of the contacts 9a and 30a , and also between the ends of the anticorona caps 16a and the electrode 13 , because the insulation distances are sufficiently large . it should be observed that in the open configuration of the circuit breaker ( fig5 ), the distance between the end of the cap 16a of the moving main contact 16 , and the electrode 13 is less than the distance between the respective ends 9a and 30a of the arcing contacts 9 and 30 . it is this feature that makes it possible to insert the resistor 3 temporarily during the operation of closing the circuit breaker . it is the anticorona cap 16a that comes close first to the insertion electrode 13 . when the distance between these two pieces becomes less than the insulation distance ( fig6 ), an arc is struck between the electrode 13 and the anticorona cap 16a , thereby inserting the resistor 3 in series in the circuit of the circuit breaker . as the moving equipment continues to move , the distance between the ends 9a and 30a of the arcing contacts becomes less than the insulation distance ( fig7 ) and an arc is struck between these contacts , thereby short circuiting the resistor 3 . the dimensions of the various elements of the circuit breaker and the speed with which the moving assembly moves are designed so that the insertion lasts for a duration lying in the range of 8 milliseconds to 10 milliseconds , which is the range specified by network utilities . as the moving equipment continues to move , it returns to its initial position ( fig1 ). the above - described means for inserting resistance during closure solve the technical problems mentioned in the preamble of the present text : the mass of the elements connected to the moving assembly is reduced , with this being achieved since the additional masses come solely from lengthening the nozzle 22 , the sliding contacts 18 , and the spring 24 , and together amounts to very little extra mass ; and bulk is reduced with this problem being solved by the insertion electrode being of smaller diameter than the anticorona cap 16a of the ring of main contact fingers 16 .