Abstract: An electric switch has an arc extinguishing mechanism that includes a plurality of splitter plates located adjacent to the switch contacts. An electromagnet coil is connected between one of the contacts and a splitter plate to produce a magnetic field that drives an arc into the extinguishing mechanism. The unique electromagnet coil is formed by a lamination of a plurality of flat open loops of conductive material alternating with layers of insulation. The flat open loops are interconnected to form a helical coil.

Abstract: A movably disposed circuit breaker has a blow-out attenuator for cooling and deionizing switching gases escaping from an arc quenching chamber. The blow-out attenuator is composed of two telescopically interlocking sub-members. The one sub-member is fixedly arranged, while the other sub-member rests with a sealing surface on a mouth surface of the arc quenching chamber. Due to the two-part design of the blow-out attenuator, the switching-gas pressure improves the sealing action between the arc quenching chambers and the blow-out attenuator.

Abstract: A DC contactor has stationary and movable contacts. A magnet is rotatably mounted adjacent to the stationary contact within a self magnetic field produced by the flow of electric current in the stationary contact. The magnet rotates so that its magnetic field extends around the stationary contact in the same direction as the self magnetic field. When an arc forms between the stationary and movable contacts, interaction with the self magnetic field and the magnetic field drives the arc toward an adjacent extinguishing chamber.

Abstract: An electrical circuit interrupter comprising a housing with an operating mechanism disposed therein and including first and second separable main contacts disposed within the housing is taught. There is an electrically conducting first contact support which has a shape which substantially doubles back upon itself and which has parallel, spaced apart first and second legs forming a central region. An electrically insulating support member is supplied which is disposed in the central region and has a substantial portion outboard of the central region in a disposition to shield a portion of the contact support member. It also has a portion which captures the first contact support member. In addition, magnetic plates are disposed within the central region for cooperating with other closed loop magnetic plates outside of the support member for providing a slot motor action for the movable contact. An arc runner is provided which is trapped between the support member and the contact support conductor.

Abstract: Provided are non-halogen, flame-resistant, resin materials and resin magnet materials, and also electron beam controllers comprising the resin magnet materials. The resin material comprises (A) a non-halogen resin composition, (B) a metal oxide hydrate, and (C) one or both of antimony trioxide and zinc borate. The resin magnet material comprises those components (A), (B) and C), and (D) a magnetic material. In the electron beam controller, the four-pole and 6-pole convergence magnets and the two-pole purity controller magnets are made of the resin magnet materials.

Abstract: Opening electrical contacts or electrical circuit interrupters. Particularly, a design for an electrical switch having opening electrical contacts which inhibit arcing. More particularly, a circuit breaker having a micro-contact interface comprising a contact with a plurality of contact points capable of handling high steady state currents conventionally handled by small to medium size molded case circuit breakers (i.e., 0.5 A.sub.rms to 400 A.sub.rms) at distribution voltage levels (120 V.sub.rms to 600 V.sub.rms).

Abstract: An electric switch (1), in particular for electric hand tools having an electric motor operated by means of direct current. The switch (1) possesses a contact system (9) consisting of a fixed contact (10) and of a switching contact (11), an actuating member (3) for triggering a switching operation between an "off" and an "on" position of the contact system (9) acting on the switching contact (11). The contact system (9) is assigned means (18), consisting of a shield (19), for extinguishing an arc generated between the fixed contact (10) and the switching contact (11) during the switching operation. The shield (19) can be moved together with the switching contact (11) in a coupled manner, during the operation to switch the switching contact (11) from the "on" to the "off" position the shield (19) being moved into the region located between the fixed and switching contacts (10, 11).

Abstract: A circuit interrupter including an operating mechanism and separable main contacts interconnected with load and line terminals has an interface region between the top and bottom portions of the completed housing thereof, which may be of reduced cross section relative to the remainder of the side walls of the circuit interrupter for being moved or pushed outwardly under the pressure of expanding gas during a circuit interruption operation. To more easily clear or separate abutment surfaces by near lateral movement thereof to provide a small opening for pressurized gas to escape the elasticity of the side wall is utilized for this purpose. Provided that the elasticity limit is not exceeded, the wall will return to its original position sealing the internal portions of the circuit interrupter from the exterior once the gas pressure has dropped below a predetermined level.

Abstract: A device for protection against overload of the switching contacts (22, 23) of a switching device (6) has an energy transducer (5) which is arranged near the switch contacts (22, 23) and is exposed to electromagnetic radiation emanating from an electric arc occurring at the switch contacts (22, 23). If the switch contacts (22, 23) are separated electrodynamically due to an overload, the energy transducer causes the circuit to be shut down by tripping solenoid (1) of a power circuit-breaker (6), for example.

Abstract: A method and apparatus for interrupting the flow of electrical current in a multiphase circuit path between at least one source and at least one load including a circuit breaker having an electro-mechanical assembly and a blade carrier corresponding to each phase of the multiphase circuit path and a phase barrier between each blade carrier. The blade carriers are interconnected, preferably, with a crossbar wherein, when one or more phases of the circuit path are interrupted, opening one or more of the blade carriers, the crossbar moves all of the blade carriers to open positions. The phase barrier is positioned circumferentially around the crossbar between each blade carrier and includes a thermoplastic material. The electro-mechanical assembly is housed within a circuit breaker enclosure having an insulating base wall and cover wall. The phase barrier has a main body planar surface perpendicular to the blade carriers and extending from the base wall to the cover wall.

Abstract: An arc chute assembly for a circuit breaker includes a plurality of U-type grids respectively including an engagement protrusion extended from each side thereof, the engagement protrusion having a key pin opening formed therethrough, a plurality of side walls respectively including a plurality of engagement slots formed therethrough, and a key pin inserted through corresponding ones of the key pin openings formed through the engagement protrusions which are inserted through the side walls and extended to an extent from an outer surface of each of the side walls. The apparatus employs the key pin for fixing the grids to the side walls, thereby facilitating assembly steps as well as decreasing an assembly time thereof.

Abstract: An electromagnetic switching device for operationally switching currents in the load range and having an instantaneous release, connected in series, for protection against welding of the contacts (6) in the overload range is created, and has a high reliability and low overall volume. The electromagnet (2) of the switching device (1) is arranged in the middle relative to the contact bridge carrier (8) and coupled directly to the latter in the middle. The instantaneous release (3) acts via a rocker (15) on the movable contact (6) and is actuated only in the case of overcurrents, use being made of the fact that only the directly coupled drive system of the switching device is employed in the nominal current range.

Abstract: An electric arc extinguishing mechanism for an electric current switching apparatus employs a plurality of splitter plates in a conventional arc chute arrangement. Each splitter plate has a pair of permanent magnet structures that produce a magnetic field which interacts with the arc causing the arc to move continuously about the surface of the splitter plate until the arc is extinguished. Such movement prevents the arc energy from being concentrated in one spot which could melt the splitter plate.

Abstract: An electric motor control apparatus includes an electrical current control apparatus which is operable to limit current to an electric motor. When the electric motor is a three-phase motor, three current limiting switch assemblies are provided in the electric current control apparatus. A single stack of laminations concentrates magnetic fields emanating from conductors in all three current limiting switch assemblies. Each of the current limiting switch assemblies includes two movable contacts which are mounted on contact arms. The contact arms are movable in slots in the stack of laminations. A first series of splitter plates is disposed in an array along a path of movement of the contact on the first movable contact arm and a second series of splitter plates is disposed along a path of movement of the contact on the second contact arm for each of the current limiting switch assemblies. A short circuit splitter plate conducts electrical current between the two series of splitter plates.

Abstract: An electric arc extinguishing mechanism is provided for an electric current switching apparatus of the type having a pair of contacts which selectively engage to complete an electric circuit. The mechanism includes a plurality of splitter plates located adjacent to the contacts and formed of electrically conductive material. Each splitter plate has a body of electrically conductive material, and a casing with a pair of planar portions on opposite sides of the body and connected by the curved edge portion. The edge portion is adjacent the contacts with the planar portions extending from the edge portion in an open loop having a gap. Any arc introduced between adjacent splitter plates moves around the open loop before being extinguished thereby not residing in one spot long enough to cause gross melting and associated erosion of the splitter plate.

Abstract: A compact current limiting circuit breaker utilizes a polymer current limiter, an arc rail and an arc gap for effective overcurrent protection. Upon the occurrence of contact separation an arc is drawn between the circuit breaker contacts and driven toward an arc rail. Commutation of the arc from the stationary contact to the arc rail effectively changes the current path to incorporate the polymer current limiter which rapidly suppresses the overcurrent. Circuit isolation is achieved by extinction of the arc within the arc gap between the movable contact and the arc rail.

Abstract: A circuit breaker having a movable load contact arm (14'), which pivots between an open position and a closed position, and a stationary line contact arm (16'). The circuit breaker includes an arcing contact structure (210) which is pivotally mounted on the stationary line contact arm. The arcing contact structure is generally "J" shaped, having a straight portion and a curved portion. The straight portion includes a bearing surface (211) which engages a bearing surface (221) on the bottom side of the line contact arm. The curved portion of the arcing contact extends beyond the end of the line contact arm and includes an electrical contact (212) which extends above the line contact arm when the load contact arm is in the open position.

Abstract: A bent roundabout current path (8d) rising in the shape of an inverted U is formed between a horn portion (8a) and the end portion of a fixed contact (1) where an arcing horn (8) is joined to the fixed contact (1). An arc (12) is subjected to the electromagnetic force directed to an arc-extinguishing chamber side from the magnetic field H of an current I flowing through the arc-(12)-side conductor portion of the roundabout current path (8d). Therefore, the moving-contact-(4)-side foot of the arc (12) is retained in the leading end portion of the moving contact (4) and not returned to the movable contact (3) side.

Abstract: An arc isolation shield for molded case circuit breakers is inserted between the circuit breaker case and cover and attached to one leg of the operating cradle. The knee of the circuit breaker moveable contact arm contacts the bottom of the shield and moves the shield in unison with the contact arm to protect the contact arm, contact braid and operating spring upon contact separation under severe overcurrent conditions.

Abstract: A power switch has a pole unit with a switch contact arrangement, an arc quenching device and a flow channel. Switching gases from the arc quenching device are provided into the flow channel and, after cooling, provided to the side of the switch contact arrangement away from the arc quenching device. The entire gas chamber of the power switch is essentially sealed. The flow channel may include a valve flap and a deionising device.

Abstract: A circuit breaker thermal-magnetic trip unit for arcing fault detection includes a current transformer having a gapped magnetic core arranged around the load side of the trip unit. The bimetal within the trip unit is positioned abutment with the gap in the transformer core to thereby heat the bimetal causing the bimetal to trip and separate the circuit breaker contacts.

Abstract: Methods of arc suppression connecting a PTC material in parallel with a pair of contacts but in series with a second pair of contacts. The PTC material could be doped-BaTiO.sub.3 -ceramics, conductive polymer, or metallic PTC materials. The two pairs of contacts should be so mechanically associated that the second pair of contacts must be always opened right after the opening of the first pair. It is enough for some applications to connect one pair of contacts in parallel with a polyswitch or BaTiO.sub.3 -ceramics. For medium and high voltage circuit breakers, more than two pairs of contacts may be needed, and all these contacts should be opened sequentially during a circuit interruption. According to the methods, simple structured circuit breakers can be made to protect circuits from a short circuit, an overload and a ground fault. The circuit breaker invented here can provide an electronic alarm signal when a fault current occurs.

Abstract: A method for interrupting electrical power between two conductors is provided, including biasing an electrically conductive element into a conducting position between two contact regions of the conductors. The contact regions are preferably portions of arc runners coupled to the conductors. The conductors surround a magnetic core that generates an electromagnetic field due to current in the conductors. The conductive element is repelled to a non-conducting position by the electromagnetic field in response to an overcurrent condition in the conductors. A secondary response mechanism is moved in response to the overcurrent condition to maintain the conductive element in the non-conducting position. For more gradually occurring overcurrent conditions, the secondary response mechanism is attracted toward the core, displacing the conductive element to the non-conducting position.

Abstract: In an electrical switching device including a stationary contact carrier having a stationary contact mounted thereon, a contact carrier assembly comprises a movable contact carrier and an arc-resistant protective shield. The movable contact carrier has a movable contact mounted thereon. The movable contact carrier is movable between a closed position and an open position. The movable contact abuts the stationary contact while the movable contact carrier is in the closed position, and the movable contact is separated from the stationary contact while the movable contact carrier is in the open position. The arc-resistant protective shield is mounted to the movable contact carrier and surrounds the movable contact. The shield protects the movable contact carrier from electrical arcs generated during circuit interruption.

Abstract: A circuit interrupter provides a conducting path between two conductors and interrupts the conducting path in response to overcurrent conditions in the conductors. The interrupter includes a magnetic core around which the conductors are disposed. Each conductor is electrically coupled to an arc runner and a spanner is biased into contact with the arc runners to compete a conducting path between the conductors. A secondary response mechanism is provided adjacent to the core and includes arms extending around the core and a magnetic body. In response to overcurrent conditions of a first magnitude the body of the secondary response mechanism is attracted to the core causing the arms to displace the spanner out of contact with the arc runners. In response to overcurrent conditions of a second magnitude, such as due to direct short circuits, the spanner is repelled rapidly to a non-conducting position and the secondary response mechanism is attracted to the core to hold the spanner in the non-conducting position.

Abstract: A relay includes a plastic enclosure, contacts disposed in the plastic enclosure for selectively operating to make and/or break at least one electrical connection, a gas filling containing at least one electronegative gas, and a sealed plastic encapsulation for preventing the at least one electronegative gas from diffusing away, whereby the dielectric strength of the at least one electronegative gas is maintained throughout the intended life of the relay.

Abstract: An electrical protection apparatus is disclosed, including a circuit breaker and an effector. The circuit breaker includes a first switch circuit including stationary and movable contacts, provided between input and output terminals. The effector includes a second switch circuit that is provided in series with the first switch circuit. Further, the circuit breaker includes an actuating mechanism for opening the contacts, electromagnetic and thermal trip devices for controlling the actuating mechanism, and first and second guiding horns spaced apart from each other and defining therebetween an arc extinguishing chamber. The first arc guiding horn is electrically connected with the movable contact to the input terminal, while the second arc guiding horn includes a switching electrode extending therefrom, the switching electrode being spaced apart from the stationery contact via an insulating gap.

Abstract: A circuit breaker comprises high-duty arc-quenching means 23 and a latching mechanism 19, which is adapted to be electromagnetically and thermoelectrically unlatched by means of a snap-action bimetal disk 52 to open contacting means 21 in response to an overload. The snap-action bimetal disk 52 is held in a carrying body 32, which has a high thermal conductivity and which carries an electromagnetic exciter coil 33 and contains an associated plunger 42. For tripping in response to an overload, the plunger 42 is adapted to be actuated either electromagnetically and/or by the snap-action bimetal disk 52. The movable contact 21 will remain open when the latching mechanism 19 has been unlatched. In response to a movement of the plunger 42 out of its make position, the latching mechanism 19 is unlatched by a first arm of a two-armed lever 37, which is made of lucite and is pivoted to the carrying body 42. The contacting means 21 are adapted to be struck open by the second arm 41 of the lever 37.

Abstract: An electrical switch device with separable contacts is provided with a shunt conductor adapted to receive one end of the arc that is struck when the contacts separate after it has jumped a dielectric gap. The shunt conductor determines an interim arc current path in which is a current limiter device.

Abstract: An electromechanical switch of the contactor or circuit-breaker type with adjacent contacts, which are provided on respective mobile and fixed contact parts. This arrangement defines a narrow ionization slot which is maintained at the start of contact opening in order to cause a secondary arc to fire substantially perpendicular to the contact opening direction constituting a shunting arc to eliminate the time duration of the contacts and switch legs.

Abstract: A miniature circuit breaker with two thermal-magnetic poles has an electronic trip device providing ground fault, and sputtering arc fault (if desired), protection located entirely in a large central compartment of a molded housing between compartments housing the two mechanical poles. The current rating of the circuit breaker is increased by a gas vent channel extending between the two mechanical pole compartments adjacent the respective breaker contacts which allows gases generated by arcing during current interruption to expand into both outer compartments, thereby permitting the circuit breaker to interrupt larger short circuit currents. The gas vent channel extends through, but does not communicate with, the central electronics compartment.

Abstract: A molded case circuit breaker enclosure and operating components are provided with additional features to enable compliance with a variety of international electrical requirements for sales in the world market. The circuit breaker operating handle is prevented from returning to the OFF position upon contact welding as one example. Another modification includes a reinforcement and rejection pin used with the enclosure case. A further modification includes a shield used with the movable contact arm to prevent the arc gas contaminants from contacting the circuit breaker operating springs.

Abstract: A mid terminal for a double break circuit breaker comprises first and second elongated conductive plates, where each of the plates have first and second ends. The second end of the first plate is longitudinally spaced from the first end of the second plate and the first end of the first plate is connected to the second end of the second plate by a lateral conductive plate. A first are runner is electron beam welded to the second end of the first plate, and a second are runner is electron beam welded to the first end of the second plate. The first and second arc runners are preferably made of steel. A first stationary contact is mounted on the first plate adjacent the first arc runner, and a second stationary contact is mounted on the second plate adjacent the second arc runner.

Abstract: A self-contained current limiter unit allows lower short-circuit-rated circuit breakers to be utilized within industrial applications. The unit is electrically-connected in series with the circuit breakers and the protected load to limit the short circuit current to a fixed predetermined value while the circuit breaker trip unit responds to interrupt the circuit current. A single unit can be arranged in electrical series connection with a plurality of lower short-circuit-rated circuit breakers to allow a substantial savings in component and equipment costs.

Abstract: Molded insulating shell halves are secured together around a blowout coil, stationary and movable contacts to pivotally trap an armature assembly therebetween. Windows are provided in the shell halves to ventilate the electromagnet coil during operation. The electromagnet is removable through the window without disassembly of the contactor. Contact and armature adjustment is accomplished through additional window openings. An arc chute having left and right-hand arc extinguishing chambers each sub-divided into upper and front chambers splits the arc into four series segments and increases the overall length of the arc significantly over similar prior art devices.

Abstract: An electric circuit-breaker of the magnetic arc extinction type includes a fixed contact member comprising two electrically insulative parts. An auxiliary part of the fixed contact member is connected to an auxiliary terminal and includes an arc deflector branch so disposed that when the contacts open the current flows in opposite directions in this branch and in the mobile contact member.

Abstract: A molded case circuit breaker controlled by an electronic trip unit is cost-competitive with electromagnetic circuit interruption devices. A novel contact arm assembly and shield arrangement in combination with a contact arm spacer and operating cradle interface reduces the assembly time and the number of operating components to effect significant cost savings.

Abstract: The present invention provides an arc extinguishing device for disposition along a pre-determined path of movement between two electrical contacts in an electrical distribution device. The device includes a generally U-shaped member having a bight portion defined by a bottom wall with two upstanding side walls. The bight portion has sufficient width to allow the movement of the electrical contacts between the two side walls. A pair of magnetic poles having a magnetic field therebetween is formed with and located near the top edge of each side wall. The device includes means for focusing the magnetic field along the longitudinal center axis through the length of the U-shaped member and in the plane overlapping the path of movement of the electrical contacts so as to increase the magnetic flux density encountered by the electrical contacts.

Abstract: An arc suppressing switch having a plurality of discrete conductors operative to allow a flow of electricity between a pair of terminals along each of the plurality of discrete conductors when the switch is closed. The conductors are oriented to distribute the total current flowing through the switch among the discrete conductors; and so that the current in each of the discrete conductors is substantially simultaneously interrupted when the switch is opened to prevent the production of an arc across the gap created at the break. The switch preferably has an intermediate contact layer containing the plurality of discrete conductors positioned between internal contact plates so that when the switch is closed a first side of the intermediate layer contacts one of the contact plates and a second side of the intermediate layer contacts the other contact plate to allow a flow of electricity between the pair of contact plates along each of the plurality of discrete conductors.

Abstract: An industrial rated molded case circuit breaker fitted with an exhaust arc gas manifold arranged over ventilation slots of the circuit breaker and disposed at a line end thereof to redirect the arc exhaust gases exiting the ventilation slots. The exhaust arc gas manifold is fixedly attached to the circuit breaker to prevent an electric fault from occurring between the different phases of a multi-phase electric power distribution system connected to the line end of the circuit breaker. An electric fault is further prevented between the exiting arc gases and the line terminals attached to the circuit breaker thereof.

Abstract: A dust preventing device for an electromagnetic contactor prevents foreign matters accumulated on a foreign matter preventing wall from slipping off the wall due to vibrations of electromagnetic contactor. In a case where an arc extinguishing chamber cover is disposed to cover a fixed contact and a movable contact, and includes a foreign matter preventing wall provided under a gas discharging opening formed on the cover, the foreign matter preventing wall is formed with ribs provided therearound in a shape of an embankment. Therefore, foreign matters having entered through the gas discharging opening can be positively trapped in a hollow portion surrounded by ribs, so that the foreign matters do not fall into the electromagnetic contactor from the foreign matter preventing wall due to vibrations of the contactor.

Abstract: A molded plastic current limiting circuit breaker having for each pole, a stationary and movable contact separable upon occurrence of a current higher than a predetermined level. The stationary and movable contacts are positioned inside an over-molded magnet opening to greatly increase the magnetic repulsion force between them and rapidly accelerate their separation by concentrating the magnetic fields generated upon an occurrence of a high level short circuit. The over-molded magnet is composed of a plurality of steel plates grouped together and being over molded with a thermoplastic material. The thermoplastic material has grooves integrally formed therein for retaining insulator inserts that protect the thermoplastic material during separation of the stationary and movable contacts.

Abstract: A molded gasket for a line conductor in a circuit breaker acts as a gas seal to prevent ionizing gases resulting from a circuit interruption from flashing over and causing phase-to-phase and phase-to-ground faults. The molded gasket includes provisions for sealing the line conductor at the interfaces with the circuit breaker housing as well as providing a barrier for the movable contact arm assembly.

Abstract: An arc gas controller-insert is used with molded case circuit breaker covers to direct the flow of arc gases that occur during intense overcurrent circuit interruption. The gas controller-insert provides access to the line and load terminal lugs for connection with and disconnection from an associated electrical power distribution system while controlling the egress of the arc gases.

Abstract: Rapid extinguishing of the arc in a circuit breaker is accelerated by a booster loop which extends parallel to an arc runner, but carries current in a direction opposite to the direction of current flow in the arc runner. The booster loop and arc runner are formed from a single piece of rigid conductor material, preferably stamped to form mounting lugs and bent over into a U-shaped configuration. In a preferred embodiment, the breaker internal connections are arranged such that current flows through a thermal overload sensor when the contacts are closed, but transfers to the booster loop and arc runner after arc current termination transfers from one of the contacts to the arc runner, thus reducing short circuit current duration through the thermal sensor.

Abstract: Since industrial-rated circuit breakers are often located remote from the associated protected electrical equipment it is often times necessary to monitor the operation of such electrical equipment by observing the condition of the circuit breaker contacts to ensure that such equipment remains operational. When a plurality of such circuit breakers are mounted within a common enclosure, an auxiliary device within each of the circuit breakers readily provides visual indication of the ON-OFF condition of the circuit breaker contacts. With such auxiliary devices, an actuator-reset lever is used to interface between the circuit breaker operating mechanism, the circuit breaker trip mechanism and the auxiliary device to activate the auxiliary device when the circuit breaker contacts are open and closed and to reset the trip mechanism when the circuit breaker contacts are opened.

Abstract: An arc gas controller-insert is used with molded case circuit breaker covers to direct the flow of arc gases that occur during intense overcurrent circuit interruption. The gas controller-insert provides access to the line and load terminal lugs for connection with and disconnection from an associated electrical power distribution system while controlling the egress of the arc gases.

Abstract: A remotely controllable circuit breaker has an improved scheme for effecting rapid arc extinction as well as protecting the breaker contact from the resulting arc current. The breaker includes first and second movable contacts 11 and 12 which are held respectively on parallel extending first and second contact arms 31 and 32 and are driven individually by a switching mechanism 20 including a manual handle 22 with a contact trip capability and by a remotely controllable switch 60. An arc runner 115 is connected to be in the same electrical potential as the second contact arm 32 and extends in the contact separating direction for receiving the one end of the arc developed between the rapidly separating contacts 11 and 12 and guiding the arc toward an arc extinguishing chute 110 as the first contact 11 moves away from the second contact 12.

Abstract: A refractory fiber insert within the cover of a molded case circuit breaker interfaces between the interior of the circuit breaker cover and the top surface of the circuit breaker arc chute to prevent the arc by-products generated within the arc chamber from re-entering the arc chamber. A shaped slot formed within the fiber insert automatically compensates for manufacturing tolerances to precisely locate the insert between the cover interior and the top surface of the arc chute.

Abstract: A Hall effect device is located in a focused gap of a flux concentrator disposed over one power terminal of a D.C. switching contactor to monitor flux induced by current flow. Magnetic fields from permanent magnets of the switching apparatus are shielded from the flux concentrator by a cup-shaped magnetic ring surrounding the concentrator, magnetically spaced therefrom, and a magnetic plate of the apparatus which is modified to accept more flux in a localized area of the sensor before saturation. The gap of the concentrator in which the Hall effect device is located is particularly positioned at a point where the magnetic field gradient from the permanent magnet field is minimum.