Abstract:
A fault indicator for detecting the occurrence of a fault current in a monitored conductor and providing a light indication thereof includes a rotatably mounted indicator flag. The flag is positioned in either a reset indicating or a fault indicating state by a magnetic pole piece, which is magnetized in one magnetic direction or the other by momentary application of a current in one direction or the other to an actuator winding on the pole piece. A magnetically actuated reed switch in an auxiliary magnetic circuit comprising an auxiliary pole piece magnetized by the actuator winding and a bias magnet magnetically aligned to oppose the reset magnetic orientation and reenforce the trip magnetic orientation of the magnetic pole piece closes upon occurrence of the fault current to connect an internal lithium battery to an LED visible from the exterior of the fault indicator housing.

Description:
This application a continuation of application Ser. No. 09/070,224, filed Apr. 30, 1998, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates generally to current sensing devices for electrical systems, and more particularly to resettable alternating current fault indicators. 
     Various types of self-powered fault indicators have been constructed for detecting electrical faults in power distribution systems, including clamp-on type fault indicators, which clamp directly over cables in the systems and derive their operating power from inductive coupling to the monitored conductor, and test point type fault indicators, which are mounted over test points on cables or associated connectors of the systems and derive their operating power from capacitive coupling to the monitored conductor. Such fault indicators may be either of the manually reset type, wherein it is necessary that the indicators be physically reset, or of the self-resetting type, wherein the indicators are reset upon restoration of line current. Examples of such fault indicators are found in products manufactured by E.O. Schweitzer Manufacturing Company of Mundelein, Ill., and in U.S. Pat. Nos. 3,676,740, 3,906,477, 4,063,171, 4,234,847, 4,375,617, 4,438,403, 4,456,873, 4,458,198, 4,495,489, 4, 4,974,329, and 5,677,678 of the present inventor. 
     Detection of fault currents in fault indicators is typically accomplished by means of magnetic switch means such as a magnetic reed switch in close proximity to the conductor being monitored. Upon occurrence of an abnormally high fault-associated magnetic field around the conductor, the magnetic switch actuates a trip circuit which produces current flow in a trip winding to position an indicator flag visible from the exterior of the indicator to a trip or fault indicating position. Upon restoration of current in the conductor, a reset circuit is actuated to produce current flow in a reset winding to reposition the target indicator to a reset or non-fault indicating position. 
     In certain applications, such as where the fault indicator is installed in a dark or inaccessible location, the need arises for a light indication in addition to the flag indication. Repair crews can then more easily find the location of the fault. 
     Because of the compact construction and limited power available in self-powered fault indicators it is preferable that the light indication be provided with minimal additional circuitry and structure within the fault indicator while providing reliable and extended operation following occurrence of a fault. The present invention is directed to a novel fault indicator light circuit which meets the above requirements by utilizing a magnetic winding, such as the actuator winding of the electro-mechanical indicator flag assembly typically utilized in fault indicators, in conjunction with a magnetic circuit to connect an internal battery upon occurrence of a fault. 
     Accordingly, it is a general object of the present invention to provide a new and improved fault indicator having a light indication of fault occurrence. 
     It is a more specific object of the present invention to provide a new and improved self-powered fault indicator which provides a light indication for an extended period of time following occurrence of a fault current in a monitored conductor. 
     It is a still more specific object of the present invention to provide a fault indicator wherein a light-indication is provided utilizing the electromagnetic flag indicator assembly of the fault indicator in conjunction with an internal battery. 
     SUMMARY OF THE INVENTION 
     The invention is directed to a fault indicator for indicating the occurrence of a fault current in an electrical conductor. The fault indicator comprises a housing, a battery, a lamp operable from the battery and viewable from the exterior of the housing, a magnetic circuit including a magnetic pole piece, a magnetically actuated switch and a bias magnet, the bias magnet having a magnetic polarity which opposes a magnetic field in the magnetic pole piece in one direction, and reenforces a magnetic field in the magnetic pole piece in the other direction, whereby the magnetically actuated switch is conditioned to open in response to a magnetic field in the one direction and closed in response to a magnetic field in the other direction, means including a magnetic winding in magnetic communication with the magnetic pole piece and responsive to the current in the monitored conductor for developing a magnetic field in the magnetic pole piece in the one direction to condition the switch open during normal current flow in the monitored conductor, and for developing a magnetic field in the magnetic pole piece in the opposite direction to condition the switch closed upon occurrence of a fault current in the conductor, the magnetically actuated switch connecting the battery to the lamp whereby the lamp lights in the fault indicating state. 
     The invention is further directed to a fault indicator for indicating the occurrence of a fault current in an electrical conductor. The fault indicator comprises a housing, a battery, a lamp operable from the battery and viewable from the exterior of the housing, an indicator flag assembly including an indicator flag viewable from the exterior of the housing and a first magnetic pole piece, the indicator flag being magnetized and in magnetic communication with the first magnetic pole piece whereby the indicator flag is actuated to a reset-indicating position by a magnetic field in the first magnetic pole piece in one direction, and is actuated to a fault-indicating position by a magnetic field in the first magnetic pole piece in the opposite direction, a second magnetic pole piece, a magnetically actuated switch and a bias magnet, the bias magnet having a magnetic polarity which opposes magnetic field in the second magnetic pole piece in one direction, and reenforces magnetic field in the second magnetic pole piece in the other direction, whereby the magnetically actuated switch is actuated open in response to a magnetic field in the one direction and closed in response to a magnetic field in the other direction, means including a magnetic winding in magnetic communication with the first and second magnetic pole pieces and responsive to the current in the monitored conductor for developing a magnetic field in the one direction in the pole pieces to position the indicator flag in the reset indicating position and condition the magnetically actuated switch in the first state during normal current flow in the monitored conductor, and for developing a magnetic field in the opposite direction in the pole pieces to position the indicator flag in the fault indicating position and condition the magnetically actuated switch closed upon occurrence of a fault current in the conductor, the magnetically actuated switch connecting the battery to the lamp whereby the lamp lights in the fault indicating state. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The invention, together with the further objects and advantages thereof, may best be understood by reference to the following description taken in conjunction with the accompanying drawings, in the several figures of which like reference numerals identify like elements, and in which: 
     FIG. 1 is a perspective view of an inductively powered clamp-on fault indicator constructed in accordance with the invention installed on a cable within a power distribution system. 
     FIG. 2 is a top plan view of the fault indicator of FIG. 1 showing engagement between the fault indicator and the cable. 
     FIG. 3 is a cross-sectional view of the fault indicator of FIGS. 1 and 2 taken along line  3 — 3  of FIG.  2 . 
     FIG. 4 is a cross-sectional view of the fault indicator of FIGS. 1-3 taken along line  4 — 4  of FIG.  3 . 
     FIG. 5 is a perspective view, partially in section, showing the principal components of the indicator flag assembly utilized in the fault indicator of FIGS. 1-4. 
     FIG. 6 is a cross-sectional view of the indicator flag assembly taken along line  6 — 6  of FIG.  5 . 
     FIG. 7 is an enlarged cross-sectional view of the auxiliary contacts of indicator flag assembly taken along line  7 — 7  of FIG.  5 . 
     FIG. 7A is a cross-sectional view of the indicator assembly taken along line  7 A— 7 A of FIG.  7 . 
     FIG. 7B is a cross-sectional view of the indicator assembly taken along line  7 B— 7 B of FIG.  7 . 
     FIGS. 8A and 8B are diagrammatic views of the principal components of the indicator flag assembly of the fault indicator in a reset indicating position. 
     FIGS. 9A and 9B are diagrammatic views similar to FIGS. 8A and 8B, respectively, showing the principal components of the indicator flag assembly in transition between a reset indicating position and a fault indicating position. 
     FIGS. 10A and 10B are diagrammatic views similar to FIGS. 8A and 8B, respectively, showing the principal components of the indicator flag assembly in a fault indicating position. 
     FIG. 11 is an electrical schematic diagram of the circuitry of the fault indicator shown in FIGS. 1-5. 
     FIG. 12 is an enlarged view of the battery holder utilized in the fault indicator of FIGS.  1 - 11 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to the Figures, and particularly to FIG. 1, a clamp-on current-reset fault indicator  20  constructed in accordance with the invention for indicating fault currents in an electrical feeder or distribution cable  21  is seen to include a circuit module  22  and an integral indicator module  23 . The indicator module  23  projects from the front face of the circuit module so as to be easily viewed when the fault indicator is installed. In accordance with conventional practice, the circuit module is attached to the outer surface of cable  21 , which may include a central conductor  25 , a concentric insulating layer  26 , and an electrically-grounded rubber outer sheath  27 . 
     Basically, circuit module  22  includes a housing  30  within which circuitry for sensing fault currents and actuaing indicator module  23  is contained, and a magnetic core assembly  31  for attaching the module to a monitored conductor (such as cable  21 ) and for providing sufficient magnetic coupling to the conductor to power the circuitry of the circuit module. The core assembly is preferably formed as a closed loop of generally rectangular configuration so as to completely encircle cable  21 , and includes a gap  32  by which the core can be opened to facilitate installation on or removal from a monitored conductor. A hook  33  on the core and an eye  36  on housing  30  may be provided to allow use of a conventional hotstick during installation or removal. A spring  34  holds the gap closed and presses the monitored cable  21  into a V-shaped recess  35  on housing  30 . A battery holder  28  positioned on the side of housing  30  includes a removable end cap  29  which provides access to a cylindrical battery compartment within which a battery  36  (FIG. 3) is contained. 
     The indicator module  23  also includes, in accordance with conventional practice, a status-indicating flag  40  for indicating circuit status. The flag  40  may be viewed through a window  41  at the front of the indicator module. 
     In operation, during normal current flow in conductor  21 , indicator flag  40  is positioned by circuitry in circuit module  22  so as to present a white or reset condition-indicating surface  40 A to the viewer. Upon the occurrence of a fault current in the conductor, the indicator flag is repositioned by the circuitry so as to present a red or fault-indicator surface  40 B to the viewer. 
     Referring to FIG. 2, the core assembly  31  of circuit module  22  may consist of a plurality of individual strips or laminations formed of oriented silicon steel arranged side-by-side in a generally rectangular closed-loop configuration. The core assembly is preferably encapsulated in a layer of resin epoxy insulating material. The rectangular configuration includes a generally rectilinear first or left side portion  42 , a generally rectilinear second or right side portion  43  opposed to first portion  42 , a generally rectilinear third or bottom portion  44  and a generally rectilinear fourth or top portion  45  opposed to third portion  44 . The closed loop consisting of side portions  42 - 45  includes gap  32  at the juncture of left side core portion  42  and bottom core portion  44 . The left side portion  42  is drawn toward the right side portion  43  by a helical spring  34  which extends between the two opposite sides of the core. 
     To provide operating power for the fault indicator circuit module  22  includes a magnetic winding  50  in magnetic communication with magnetic core assembly  31 . As shown in FIGS. 2 and 3, winding  50  is coaxially positioned on the bottom portion  44  of the core assembly and is dimensioned to provide a close fit with the core cross section. The winding is preferably connected to a circuit board  51  on which the other components of the circuit module are mounted. These components include a magnetic reed switch  52 , which is positioned with its axis perpendicular to and spaced from the axis of conductor  21  so as to respond to fault currents in the conductor in a manner well known to the art. The entire assembly, consisting of winding  50 , circuit board  51 , magnetic reed switch  52  and the other components of the module, may be encapsulated in an epoxy material  53  so as to form within housing  30  at the bottom portion of core assembly  31  a weatherproof module responsive to the current level in conductor  21 . 
     Referring to FIG. 5, indicator module  23 , which may be conventional in structure and operation, includes a cylindrical plastic housing  60  within which the components of the module are contained. The projecting end of housing  60  includes a transparent section  55  through which an internal signal lamp  56  can be viewed. Within housing  60  an integral partition  61  serves as a mask and spacing element and a support for lamp  56 , and a transparent end cap  62  sonically welded to the end of the housing seals the interior against contamination while providing the viewing window  41  (FIG.  1 ). 
     A disc-shaped circuit board  63  is positioned perpendicularly to the axis of the housing. This circuit board, which may be secured in position by an epoxy material filling the rear portion of the housing, serves as mounting means for the components of the indicator module. 
     To provide an indication of the occurrence of a fault current, the indicator module includes within the lower end of housing  60  the generally disc-shaped indicator flag  40  mounted for rotation about a pivot axis  66 . As best seen in FIGS. 8-10, the face of target indicator  40  has a red segment  40 B and a white segment  40 A, only one of which is visible at a time through window  41  in the transparent end of housing  60 . 
     Secured to and pivotal with indicator flag  40  is a permanent flag magnet  67  which is formed of a magnetic material having a high coercive force, such as ceramic, and is magnetically polarized to form two magnetic poles of opposite polarity, as indicated in FIGS. 8-10, with opposite magnetic polarities along a diameter of the magnet. 
     A pole piece  68 , which is preferably formed of a magnetic material having a relatively low coercive force, such as chrome steel, in a reset condition is biased at its projecting ends of the magnetic polarities indicated in FIGS. 8A and 8B. As shown in FIG. 5 the ends of the pole piece extend along the side wall of housing  60 , in close proximity to flag magnet  67 . As a result, the opposite polarity magnetic poles of flag magnet  67  are attracted to position the indicator flag  40  to the reset or non-tripped position shown. In this position the red segment  40 B of the indicator flag is not visible through window  41 , and all that is seen is white segment  40 A. 
     On the occurrence of a fault current in conductor  21  pole piece  68  is remagnetized to the magnetic polarities shown in FIGS. 9 and 10 by momentary energization in one direction of a winding  70  on the center section the pole piece. As a result, the poles of magnet  67  are repelled by the adjacent like-polarity poles of the pole piece and indicator flag  40  is caused to rotate 180° to its tripped position, as shown in FIGS. 10A and 10B. In this position, the red segment  40 B of indicator flag  40  is visible through window  41 , and a lineman viewing the fault indicator is advised that a fault current has occurred in the conductor. 
     Indicator flag  40  remains in its fault indicating position until the ends of pole piece  68  are subsequently remagnetized to the magnetic polarities shown in FIGS.  8 A and  8 B, by momentary energization of winding  70  with a current in the opposite direction. Upon this happening, indicator flag  67 , and hence indicator flag  40 , is caused to rotate from the tripped position shown in FIGS. 10A and 10B to the reset position shown in FIGS. 8A and 8B, and the fault indicator is conditioned to respond to a subsequent fault current. 
     To preclude indicator flag  40  from becoming stalled upon reversal of the magnetic polarities of pole piece  68 , as might happen with a target perfectly centered between the poles of the pole piece and having a degree of bearing friction, the fault indicator includes an auxiliary U-shaped pole piece  71  positioned adjacent target magnet  67  coaxial with and at an angle to pole piece  68 . The existence of a magnetic field between the poles of pole piece  68  results in the production of induced magnetic poles in auxiliary pole piece  71 . As a result, upon reversal of the magnetic polarity of the poles of pole piece  68  following occurrence of a fault current the auxiliary poles exert a rotational force on the most adjacent poles of the target magnet  67 . This causes a rotational moment to be exerted on flag indicator  40  tending to turn the flag in a predetermined (counter-clockwise in FIGS. 8-10) direction such that the flag is precluded from remaining in its reset position, even if it should be perfectly positioned and have a degree of bearing friction. Once rotation has been established, as shown in FIGS. 9A and 9B, the greater force of the main pole piece  68  overcomes the effect of the auxiliary pole piece  71  and rotation continues until the flag is aligned as shown in FIGS. 10A and 10B. 
     Energization of winding  70  by current in one direction upon occurrence of a fault current in conductor  21 , and energization of winding  70  by current in the opposite direction upon restoration of current in conductor  21 , is accomplished by means of circuitry contained within circuit module  22 . Referring to the schematic diagram shown in FIG. 11, the single winding  70  of indicator module  23  is connected to the circuit module by conductors  74  and  75 . 
     Power for operation of the circuit module is obtained from pick-up winding  50 , within which an alternating current is induced in a manner well known to the art as a consequence of alternating current in conductor  21 . Winding  50  is tuned to resonance at the power line frequency by a capacitor  80  and the resultant resonant output signal is peak-limited by a pair of zener diodes  81  and  82  connected back-to-back across the winding. 
     The resonant signal is increased in voltage by a conventional voltage multiplier circuit comprising diodes  83 - 86  and capacitors  87 - 90  to develop in a manner well known to the art a direct current of sufficient magnitude for powering the circuitry of the module. 
     The positive polarity output terminal of the voltage multiplier network, formed at the juncture of diode  83  and capacitor  88 , is connected to one terminal of winding  70  through a conductor  91 , and to one terminal of a first current storage capacitor  92 . The negative polarity output terminal of the voltage multiplier network, formed at the juncture of diodes  86  and capacitor  90 , is connected to the remaining terminal of capacitor  92 , and through a forward-biased diode  93  and a current limiting resistor  94  to one terminal of a second current storage capacitor  95 . The other terminal of capacitor  95  is connected to the remaining terminal of winding  70  through a conductor  96 . With this arrangement, capacitor  92  is charged directly, and capacitor  95  is charged through winding  70 , by the unidirectional current developed by the voltage multiplier network during normal current flow in conductor  21 . 
     To provide for periodic energization of winding  70  during normal current flow in conductor  21 , the remaining end terminal of winding  70  is connected through a first switch device in the form of a silicon controlled rectifier (SCR)  97  to the negative polarity terminal of capacitor  92 . Periodic conduction through SCR  97  is obtained by connecting the gate electrode of that device to the positive polarity output terminal of the voltage multiplier network through a voltage divider network comprising a pair of resistors  98  and  99  and a bilateral diode  100 . SCR  97  is periodically triggered into conduction when the voltage developed across bilateral diode  100  as a result of capacitor  97  being charged by the voltage multiplier network reaches the threshold level of the diode. This causes a current flow in a first direction in winding  70 , with the result that indicator flag  40  is positioned as shown in FIGS. 8A and 8B. Diode  93  prevents capacitor  95  from being discharged through SCR  97  upon conduction of that device, leaving the capacitor available for energizing winding  70  in a reverse direction in response to a fault condition. 
     Winding  70  is energized in the reverse direction upon occurrence of a fault current in conductor  21  by discharge of capacitor  95  through a second SCR  101  having its cathode connected to the negative polarity terminal of the capacitor, and its anode connected to the first end terminal of winding  70 . Conduction is established through SCR  101  by closure of the contacts of reed switch  52 , which is connected between the positive polarity terminal of capacitor  95  and the gate electrode of SCR  101  by a network comprising a resistor  102  and a capacitor  103 , a bilateral diode  104 , and a resistor  105 . 
     Reed switch  52  is positioned within housing  30  in sufficiently close proximity to conductor  21  such that the contacts of the switch close upon occurrence of a fault current in the conductor. Upon this occurrence, the positive polarity terminal of capacitor  95  is connected through the closed contacts of reed switch  52  and the circuit comprising resistors  102  and  105 , bilateral diode  104 , and capacitor  103  to the gate electrode of SCR  101 , causing that device to be rendered conductive. This causes capacitor  95  to discharge through the SCR, energizing winding  70  in the reverse direction and repositioning indicator flag  40  as shown in FIGS. 10A and 10B. 
     To preclude the possibility of currents of opposite direction being applied to winding  70  by simultaneous conduction of SCR  101  and SCR  97 , a predetermined time delay in conduction through SCR  101  may be provided following occurrence of a fault current in conductor  21 . This is accomplished by resistor  102  and capacitor  103 , which together form an RC time constant network in the gate circuit of SCR  101 . Upon closure of the contacts of reed switch  52  it is necessary that capacitor  103  charge through resistor  102  to the threshold voltage of bilateral diode  104  before sufficient gate electrode current is supplied to SCR  101  to initiate conduction in that device. Resistor  105  serves in a conventional manner as a current drain path for the gate electrode. 
     The time delay provided is designed to insure that should a fault occur simultaneously with the periodic energization of winding  70  in a reset direction, capacitor  92  will have completely discharged prior to winding  70  being energized to signal the fault. 
     Thus, in operation winding  70  is supplied with unidirectional current in one direction from a first current storage device, capacitor  92 , and in an opposite direction from a second current storage device, capacitor  95 . Capacitor  92  is connected to one terminal of the magnetic winding, and capacitor  95  is connected to the other terminal. A first switch device, SCR  97 , periodically completes the discharge circuit for capacitor.  92  to the opposite terminal of the winding during reset conditions. A second switch device, SCR  101 , completes the discharge circuit for capacitor  95  to the opposite terminal of the winding upon the occurrence of a fault current. 
     The two current storage capacitors  92  and  95  are simultaneously charged by a charging circuit which includes the line current-powered voltage multiplier network. Capacitor  92  is charged directly and capacitor  95  is charged through winding  70 , isolation diode  93  and resistor  94 . Diode  93  provides isolation for the trip circuit upon operation of the rest circuit. 
     An auxiliary contact closure is obtained in fault indicator  20  upon occurrence of a fault current in monitored conductor  21  by providing a second magnetic circuit in indicator module  22 . In particular, and referring to FIGS.  5  and  8 - 10 , the second magnetic circuit is formed by a second U-shaped magnetic pole piece  110 , a reed switch  111  and a bias magnet  112 . Pole piece  110 , like pole piece  68 , is preferably formed of a magnetic material having a relatively low coercive force, such as chrome steel. Winding  70  wraps around both pole piece  68  and pole piece  110 , so that the direction of the magnetic field induced in both pole pieces is dependent on the direction of current in the winding. The lead wires of reed switch  111  are positioned in close proximity to the ends of pole piece  110  to complete the magnetic circuit. However, to avoid a short circuit across the switch the lead wires are electrically isolated from the pole pieces. 
     In operation, when fault indicator  20  is in a reset state with indicator flag  40  positioned as shown in FIG. 8A, and the magnetic circuit through reed switch  111  is as shown in FIG.  8 B. In the absence of bias magnet  112  the magnetic field between the poles of pole piece  110  would cause the contacts of reed switch  111  to close. However, bias magnet  112  is polarized to oppose the magnetic poles as now polarized so that the field between the poles is sufficiently weakened so that the reed switch contacts do not close and no fault is signaled. 
     Upon occurrence of a fault, the polarity of the magnetic poles of pole piece  110  changes, as shown in FIGS. 9B and 10B. Magnet  112  now works to strengthen the magnetic field applied to the reed switch contacts, and the contacts close. 
     To prevent undesired actuation of reed switch  111  from the external magnetic field associated with conductor  25  the switch is preferably aligned with its axis generally parallel to the axis of the monitored conductor. With this alignment, to avoid actuation of the switch by the stray magnetic field of winding  50 , the reed switch  111  is preferably contained within a cylindrical sleeve  116  of magnetically conductive material, such as copper, with bias magnetic  112  positioned on the outside surface of the sleeve with its axis parallel-spaced to the axis of the reed switch. However, where the monitored conductor is sufficiently spaced from the reed switch that the magnetic field of the conductor is not a factor, the reed switch can be aligned with its axis perpendicular to the axis of the actuator winding  70  as shown in FIG. 12 to minimize the effect of winding  70  on the reed switch. In this case the magnetic shield  116  may not be required. 
     The leads of reed switch Ill can be magnetically coupled to and electrically isolated from the magnetic poles of pole piece  110  by soldering or otherwise attaching the switch leads to metallic sleeves  117  which are fitted over sleeves  118  of electrically insulating material, such as vinyl, which in turn are fitted over the magnetic poles. 
     In accordance with the invention, a light indication of fault occurrence is obtained by connecting battery  36  through switch contacts  111  to a flasher circuit  120 , which provides a flashing signal to signal lamp  56 . Flasher circuit  120  is preferably a commercially available component adapted to power lamp  56 , which is preferably a light emitting diode (LED). 
     With LED  56  positioned as shown behind flag  40 , the light is viewable from the front of fault indicator  22  through the flag and window  41 , and from the sides of the fault indicator through the transparent end portion  55  of the indicator assembly housing  30 . To render the LED better viewable from the front, all or a portion of indicator flag  40  is preferably formed of a translucent material. 
     Battery  36  is preferably a thionyl chloride lithium battery, such as type TL-593-S manufactured by TADIRAN, Ltd. of Israel, which provides a constant 3.6 volt output to depletion. Flasher circuit  120  and LED  56  are preferably a single component, such as a type MLED-6970D13B/B manufactured by Microlamps, Inc. This component gives a flashing rate of approximately one per second. It will be appreciated that other flashing circuits may be used, including circuits discrete from the signal lamp. 
     Referring to FIG. 12, battery holder  28  preferably includes a cylindrical fixed portion  121  in which is provided a cylindrical metallic inner sleeve  122 . This sleeve is dimensioned to receive a cylindrical metallic outer sleeve  123  attached to cap  29 . When the cap is installed the outer sleeve fits coaxially within the inner sleeve to establish an electrical connection to the cap end of the battery. The outer sleeve is dimensioned to slidably receive the battery, which is engaged by a helical spring  124  within the cap, thus assisting in holding the battery in place when the cap is installed. A single transverse pin  125  establishes electrical connection to the other end of the battery. 
     It will be appreciated that while the interior indicator lamp arrangement of the invention has been shown incorporated in an inductively coupled current powered fault indicator, the inventive arrangement finds equal utility in capacitively coupled electrostatical power fault indicators such as those mounted on system test points, which utilize an electromagnetically actuated indicator. 
     Thus, a compact externally-powered fault indicator has been described which upon sensing of a fault current provides a contact closure for external signaling and control purposes. By utilizing the existing electromechanical indicator flag assembly, a minimal number of additional components are required, making the device especially well suited for economically upgrading existing fault monitoring systems. 
     While a particular embodiment of the invention has been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made therein without departing from the invention in its broader aspects, and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of the invention.