GB2286933A - Earth leakage detection circuit and differential transformer - Google Patents

Earth leakage detection circuit and differential transformer Download PDF

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Publication number
GB2286933A
GB2286933A GB9414931A GB9414931A GB2286933A GB 2286933 A GB2286933 A GB 2286933A GB 9414931 A GB9414931 A GB 9414931A GB 9414931 A GB9414931 A GB 9414931A GB 2286933 A GB2286933 A GB 2286933A
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United Kingdom
Prior art keywords
circuit
earth
sensing
earth leakage
transformer
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GB9414931A
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GB9414931D0 (en
Inventor
Gek Chua Chua
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Individual
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Individual
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Priority to TW83107373A priority Critical patent/TW288103B/zh
Publication of GB9414931D0 publication Critical patent/GB9414931D0/en
Publication of GB2286933A publication Critical patent/GB2286933A/en
Withdrawn legal-status Critical Current

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Classifications

    • HELECTRICITY
    • H02GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02HEMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H3/00Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection
    • H02H3/26Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to difference between voltages or between currents; responsive to phase angle between voltages or between currents
    • H02H3/32Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to difference between voltages or between currents; responsive to phase angle between voltages or between currents involving comparison of the voltage or current values at corresponding points in different conductors of a single system, e.g. of currents in go and return conductors
    • H02H3/33Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to difference between voltages or between currents; responsive to phase angle between voltages or between currents involving comparison of the voltage or current values at corresponding points in different conductors of a single system, e.g. of currents in go and return conductors using summation current transformers
    • H02H3/338Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to difference between voltages or between currents; responsive to phase angle between voltages or between currents involving comparison of the voltage or current values at corresponding points in different conductors of a single system, e.g. of currents in go and return conductors using summation current transformers also responsive to wiring error, e.g. loss of neutral, break
    • HELECTRICITY
    • H02GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02HEMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H1/00Details of emergency protective circuit arrangements
    • H02H1/0007Details of emergency protective circuit arrangements concerning the detecting means

Abstract

An earth leakage detection circuit includes a differential transformer 130 with primary coils 135/7/9 for sensing currents in live, neutral and earth lines and a secondary coil 140 for sensing a difference between the current in the live line and the sum of currents in the neutral and earth lines, and a trigger circuit 200 responsive to a difference signal from the secondary coil 140 for actuating a circuit breaker 100 if the difference exceeds a pre-determined level. The circuit may also include a plurality of detectors 170 each for sensing the level of earth leakage from a different source, the trigger circuit 200 actuating the circuit breaker 100 if any one of the detectors 170 detects earth leakage in excess of a pre-determined level. The secondary coil 140 of the transformer 130 is adjustable in position to obtain a null between primary coils and thus compensate for unequal dimensions/position of the primary coils. <IMAGE>

Description

AN EARTH LEAKAGE DETECTOR CIRCUIT 1. Field of the invention: The present invention relates to an electrical earth leakage circuit breaker.
2. Description of the related art: Earth leakage circuit breakers have been proposed in the prior art in numerous patents whereby a core balance (differential) current transformer is used for the detection of electrical earth faults and should any one of the two electrical supply wires leaks to the electrical earth by the pre-determined level, the circuit breaker will trip thereby alerting the user of the excess of leakage current. The primary coils of the core balance (differential) transformer usually consist of the "Live" and "Neutral" coils, a secondary sensing coil and a trigger circuit to energise the solenoid of the circuit breaker.
The circuitry is usually arranged in such a way that should the electrical leakage current exceeds the pre-determined level (usually 30 to 100 milli-amperes), the current induced in the secondary sensing coil will trigger the solenoid of the circuit breaker via the trigger circuit/mechanism to shut down the electrical supply.
The safety level at which the leakage current could pass through a human body without severe shock or injury is estimated to be below 10 milli-amperes with a duration of less than 250 milli-seconds. However, most of the electrical appliances in use in the homes and offices today do have certain degree of electrical leakage current and when they are used together with the same circuit breaker, the total leakage current could easily exceed the predetermined level of the circuit breaker.
This phenomenon poses a problem in selecting the predetermined level of leakage current because of the fact that if the electrical leakage current is set to a safe level of say, below 10 milli-amperes to ensure the safety of the user, then the circuit breaker is rendered useless as it would trip frequently when several electrical appliances with normal leakage current are used simultaneously. Conversely, if the pre-determined level of leakage current is set at a higher level to enable the electrical appliances with normal leakage current to be used, then the electrical leakage current setting would have exceeded the safety limit a human body could endure.
With such a dilemma, it is difficult to design the circuit breaker to protect the user from severe electrical shock or injuries as well as to provide a safe limit for all the electrical appliances in use. Moreover, with the increasing number of electrical appliances in use in the homes and offices, the risk of the user receiving an electrical shock is higher. Such increase ifl the use of electrical appliances also mean a higher electrical leakage current is required in order to prevent frequent tripping of the circuit breaker even though there was no electrical earth fault in all of the appliances in use.
Summary of the Invention It is the object of the present invention to overcome these disadvantages of the prior art described above by providing an apparatus to differentiate the difference between the electrical earth leakage current of electrical appliances and the electrical leakage current passing through a human body.
According to the invention in the first aspect there is provided an earth leakage detector circuit comprising means for sensing current flow in live, neutral and earth lines, and sensing a difference between the current flowing in the live line and the sum of currents flowing in the neutral and earth lines; and means responsive to the sensing means for actuating a circuit breaker if said difference exceeds a pre-determined level.
The preferred embodiment of the invention includes a differential current sensing transformer, CT with its primary coils consisting of the "Live", , "Neutral" and "Earth" wires and a secondary coil, S which is tuned to coincide with the local electrical mains supply frequency.
A voltage amplifying means to amplify the induced voltage of the tuned secondary coil, S in which the voltage amplifier is incorporated with a T-notch filter wired in the feedback loop of the voltage amplifier to serve as a band-pass amplifier which frequency is tuned to the local electrical mains supply frequency.
The described embodiment of the present invention provides an electronic circuitry to detect the difference between such leakage currents so that the circuit breaker can be made to respond by triggering a circuit with high sensitivity of say, below 5 milli-amperes when it senses that the electrical leakage current is flowing through a different earth/ground plane (ie a human body or any living thing) while allowing a normal pre-determined level of leakage current to flow through the electrical earth system (ie electrical appliances) without tripping the circuit breaker unless the pre-determined level designated for the electrical appliances have been exceeded.
According to the invention in a second aspect, there is provided an earth leakage detector circuit comprising a plurality of earth leakage detectors, each for sensing the level of earth leakage from a different source and means responsive to the detector for actuating a circuit breaker if any one of said plurality of detector detects an earth leakage in excess of a pre-determined level.
The described embodiment of circuit breaker of the first aspect of the invention can be incorporated with multiple earth leakage detectors of the second aspect for separate groups of electrical appliances in use with the same circuit breaker, each of which with a trip leakage current of, for example, 10 to 30 milli-amperes.
A preferred embodiment containing the first and second aspects of the invention may comprise a differential current sensing transformer which consists of three primary coils for the "Live", "Neutral", and "Earth" supply, and a tuned secondary coil to detect the electrical leakage when current is flowing through a human body to a different earth/ground plane, a band-pass voltage amplifier to amplify this weak electrical current to a suitable level, a buffer amplifier and an offset transformer to neutralise the potential difference between the Neutral and Earth Lines, a plurality of earth leakage current detectors to detect the earth leakage current of the appliances in use, a trigger circuit to combine the amplified signal from the differential current sensing transformer with the leakage current from the earth leakage detectors to trigger the solenoid of the circuit breaker and a low voltage power supply for the apparatus.
According to the invention in the third aspect, there is provided a differential current transformer having a plurality primary coils and a secondary coil for sensing current imbalance between the primary coils and wherein the position of the secondary coil relative to the primary coils is adjustable.
The differential transformer of a third aspect of the invention may comprise a core upon which the primary and secondary coils are mounted, the secondary coil being slidable on the core.
The adjustability of the secondary coil allows the secondary coil to be moved to a position to obtain a null between live and neutral coils and thus compensate for unequal physical dimensions/position of the primary coils.
Brief Description of the Drawings An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a block diagram of an embodiment of the circuit breaker with expandable earth leakage current detector transformers for electrical appliances.
Figure 2 is an earth leakage current flow circuit showing the difference between the electrical earth of an appliance and the earth/ground plane of a human body or living things.
Figure 3 is a band-pass voltage amplifier with tunable band-pass frequency to suit the frequency of the local electrical mains supply.
Figure 4 shows a trigger circuit with light-emitting diode indicators and with individual Reset switches for the different earth faults detectors.
Figure 5 shows a construction of a differential current sensing transformer.
Description of the preferred Embodiment A preferred embodiment of the present invention will be described in reference to Figure 1 and Figure 2. This apparatus basically consists of an electro-mechanical switch, 100 which serves as a circuit breaker. The input terminals, L1/N1 of the circuit breaker, 100 are connected to the "Live" and "Neutral" of the incoming electrical supply. The "Live" and "Neutral" terminals are further connected to a conventional low-voltage power supply circuitry, 110 via a step-down transformer, 120 to provide the necessary low-voltage supply (Direct Current supply) to operate the electronic circuitry.
The incoming earth line is connected to one terminal of the secondary winding of an offset transformer, 350 the primary winding of which is connected to the output of a buffer amplifier, 360. The input of the buffer amplifier 360 is connected to the Neutral line via capacitor 370, preset resistor 372 and resistor 374. This arrangement ensures that any "stray" voltage which appears between the neutral and earth lines is neutralised by adjusting the preset resistor, 372, thereby reducing the possibility of a false tripping. The "stray" voltage which appears between the neutral and earth lines is the result of the voltage dropped along the neutral line and/or earth resistance when electrical power is drawn between the live and neutral lines.The other terminal of the secondary winding of the offset transformer 350, together with the output, L2/N2 of the circuit breaker, 100 are connected to L3/N3/E1 of a differential current sensing transformer, 130 whose primary coils 135, 137, 139, consists of three separate and identical number of turns for the "Live", "Neutral" and "Earth" wirings. A fourth coil, 140 of the differential current sensing transformer, 130 serves as the secondary coil the resonant frequency of which is tuned to coincide with the local mains supply frequency by means of capacitor, 145. The secondary coil, 140 is connected to a band-pass voltage amplifier, 150 via resistor 155 and two clamp diodes, 157 and 159.The function of the resistor, 155 is to limit the high current surge and transient when the two clamp diodes, 157 and 159 are brought into action each time the electrical surge and transient are present in the electrical power lines.
The band-pass voltage amplifier, 150 is shown in more detail in figure 3 and comprises an integrated circuit amplifier, 400 biased by resistors 402, 404, having an input through broad band filter 406, 408, with a T-notch filter, 410 placed in the feed back path of the amplifier 400. The filter 410 is of standard band-pass construction including capacitors 412, 414, 416 and resistors 418, 420.
Variable resistor 422 connects ground to the connection between capacitors 412, 414 and is adjustable to provide maximum amplification at the band-pass frequency corresponding to the electrical main frequency (generally 50/60 hz).
The "Earth" coil terminal, E2 of the differential current sensing transformer, 130 is connected to terminals E3 (...
to Ex) of an earth leakage current detector transformer, 170(1) the output terminals of which E4(... to Ey) together with terminals L4 and N4 of the differential current sensing transformer, 130 are terminated as the electrical supply OUTPUT ready to be connected to all the electrical appliances in the conventional and well-known manner.
Under normal working condition, there is no signal output from the secondary coil, 140 of the differential current sensing transformer, 130 when an electrical appliance is connected to the output terminals, Live 1, Neutral 1 and Earth 1 (or Live 1, Neutral 1 and Earth n) of the apparatus because of the fact that the current flowing through the "Live" coil, 135, is equal and of the opposing phase to that flowing through the "Neutral" coil, 137 and "Earth" coil, 139. However, when the load current of the electrical appliance is high, slight electrical current imbalance between the "Live" and "Neutral" coils of the differential current sensing transformer, 130 would result in a small voltage being induced in the secondary coil, 140 because of the unequal physical dimensions/position of the "Live", "Neutral" and "Earth" coils.This problem is solved by a specially constructed differential current sensing transformer, 130 as shown in figure 5 in which the secondary coil, 140 is allowed to slide along/around its core 142 (which may be toroidal or as shown) to obtain a "null" between the "Live" and "Neutral" coils, 135, 139.
The current imbalance between the "Live" and "Earth" coils is insignificant because the current flowing (leakage current of the appliance) from the "Live" to the "Earth" is usually small. In fact, when the electrical leakage current of the appliance exceeds the pre-determined level (usually below 100 milli-amperes), the circuit breaker would have tripped by then.
The earth leakage current of the electrical appliance/s will appear across the terminals EL1 and EL2 of the earth leakage current detector transformer, 170(1). A plurality of earth leakage current detector transformers can be incorporated to provide separate groupings of electrical appliances connected to the same output terminals, Live 1 and Neutral 1 but having its earth wiring connected to a different earth terminal, such as Earth n of the earth leakage current detector transformer, 170(n).This arrangement enhances the reliability of the apparatus in such a way that the electrical earth leakage of each group of appliances within the same earth leakage current detector transformer are not compounded with the other groups of electrical appliances and the total electrical leakage current of all the electrical appliances in use, thereby preventing unwarranted tripping of the circuit breaker even though none of the electrical appliances in use are faulty of excessive earth leakage. Moreover, the grouping of separate earth leakage current detector transformer also facilitate easy identification of the faulty group of appliances in question. A trigger circuit 200, for actuating circuit breaker 100 in response to earth leakage current detector transformers 170, will now be described with reference to figure 4.
The output signal VO from the band-pass voltage amplifier, 150 is connected to input Es of the trigger circuit 200 of figure 4, via a variable preset resistor, 210 (Figure 1) which can be used to set the electrical shock leakage current in the range of 1 to 5 milli-amperes. Similarly, the output signals from the plurality of earth leakage detector transformers, 170(1) to 170(n), are connected to the inputs PS1, PS2, ... PSn of the trigger circuit 200, via the individual appliance earth leakage current variable resistor preset, 220(1) - 220(n) (Figure 1) which have the earth leakage current limit set in the range of 10 to 30 milli-amperes or any other leakage current of practical limits.
The trigger circuit basically consists of a SN74LS14 Schmitt trigger circuit 230 to toggle a SN74LS00 wired as RS Flip-flop circuit 240. The earth leakage current signals from the voltage amplifier, 150 and the plurality of the earth leakage current detector transformers, 170(1) - 170(n) are connected to the inputs of respective Schmitt triggers 230 via respective transistor emitter-follower circuits 250. The outputs Q from all the RS Flip-flop circuits, 240 are connected to a two-stage transistor driver 270 to energise the solenoid of the circuit breaker 100 via respective diodes 280. The other output Q1 from each RS Flip-flop circuit, 240 is used to drive a respective light-emitting diode indicator, 290 to facilitate easy identification of the faulty appliance.
Once the fault has been identified and rectified it is then reset by activating respective Reset switch 295 (Figure 4) before switching on the circuit breaker 100 again.
In figure 2, the earth wire connected to the electrical appliance 300 is shown to have been disconnected accidentally (marked X) and it is easy to discover that the chassis of the electrical appliance has become LIVE. The live chassis of the unearthed electrical appliance will cause an unequal current flow between the three coils 135, 137, 139 when the chassis of the unearthed electrical appliance 300 is touched by the unaware user because of the fact that the electric current has leaked through the user to a different earth/ground plane (the floor/ground) thereby causing the current flowing through coil 135 to be greater than the current flowing through coil 137 and coil 139. Such unequal flow of electric current in the three coils causes a voltage to be induced in the secondary coil, 140 of the differential current sensing transformer, 130.
The same applies when the live wire is accidentally touched by the user.
The induced voltage from the secondary coil, 140 of the differential current sensing transformer, 130 is amplified by the band-pass voltage amplifier, 150 in the manner as described earlier. The amplified signal is made adjustable and calibration can be made to correspond the triggering voltage with the desired limits of the electrical leakage current flowing through a human body.
The test switches, 300 (Appliances) and 310 (Electrical Shock) are also incorporated to facilitate periodical testing of its circuitry as shown in Figure 1, these operating by providing a short from live to earth via respective resistors connected to the output earth 1 terminal and El on either side of transformer, 130.
As can be understood from the above, the earth leakage circuit breaker according to the present invention can be of a simple configuration, ie - single earth leakage current detection with a differential current sensing transformer as described in the above invention with a fixed secondary coil, for low current operation or a more elaborate configuration with multiple earth leakage current detection terminals for multiple groups of appliances connected to the same circuit breaker and a sliding secondary coil, 140 of the differential current sensing transformer as shown in figure 5 for higher current operation.
It must be noted that the details of the design and construction of the invention may be varied and therefore it does not limit the patent hereon granted other than as indicated by the scope of the appended claims.
For example, the described embodiment combines means for sensing a leakage current on the earth lead so that any difference between live and the sum of neutral and earth currents will indicate a current leakage through another path which could be the human body and, also, the provision of multiple earth leakage current detectors for different groups of appliances to facilitate (1) easy identification of faulty appliances or groups of appliances, (2) separate and adjustable leakage current setting (sensitivity) for different loads and (3) higher reliability by ensuring that the "trace" leakage currents from one application or a group of appliances do not sum up together with other groups of appliances. However, as will be apparent to one skilled in the art, these features are independent and may be used separately one from the other.

Claims (23)

1. An earth leakage detector circuit comprising means for sensing current flow in live, neutral and earth lines; and sensing a difference between the current flowing in the live line and the sum of current flowing in the neutral and earth lines; and means responsive to the sensing means for actuating a circuit breaker if said difference exceeds a pre-determined level.
2. A circuit is claimed in claim 1 wherein the sensing means comprises a differential current sensing transformer having a plurality of primary coils corresponding to the live, neutral and earth lines and a secondary coil for sensing said difference.
3. A circuit is claimed in claim 2 wherein the secondary coil is adjustable in position relative to the primary coils.
4. A circuit is claimed in claim 3 wherein the primary and secondary coils are mounted on a yoke and the secondary coil is slidable on the yoke.
5. A circuit is claimed in any one of the preceding claims wherein the means responsive to the sensing means comprising a trigger circuit for actuating said circuit breaker when said difference exceeds the pre determined level.
6. A circuit is claimed in any one of the preceding claims further comprising means for adjusting said pre-determined level.
7. A circuit is claimed in claim 6 wherein said adjusting means comprises a variable preset resistor.
8. A circuit is claimed in any one of the preceding claims further comprising amplifier means connected between said sensing means and said response means.
9. A circuit is claimed in any one of the preceding claims further comprising a plurality of earth leakage detectors, each for sensing the level of earth leakage from a different source, the detectors being connected to said responsive means for actuating the circuit breaker when a said earth leakage exceeds a pre determined level.
10. A circuit is claimed in claim 9 wherein the earth leakage detectors each comprises a transformer for sensing current flow on a respective earth line.
11. A circuit is claimed in claim 9 or claim 10 wherein the responsive means comprises a trigger circuit having independent trigger means corresponding to each detector.
12. A circuit is claimed in any one of claims 9 to 11 further comprising means for adjusting said pre determined level of earth leakage.
13. A circuit is claimed in claim 12 wherein the means comprises a variable resistor.
14. A circuit is claimed in any one of the preceding claims wherein the responsive means includes indication means to indicate when the circuit has been triggered.
15. A circuit is claimed in claim 14 wherein the indication means comprises a light emitting diode.
16. A circuit as claimed in any one of the preceding claims further comprising voltage compensation means for compensating for voltage difference between the neutral and earth lines.
17. A circuit as claimed in claim 16 wherein said voltage compensation means comprises voltage sensing means, amplifying means for producing a compensation voltage and means for applying said compensation voltage to the earth line.
18. A circuit as claimed in claim 17 wherein said applying means comprises a transformer.
19. A circuit as claimed in 17 or claim 18 wherein said sensing means comprises an tunable RC circuit.
20. An earth leakage detector circuit comprising a plurality of earth leakage detectors each for sensing the level of earth leakage from a different source and means responsive to the detectors for actuating a circuit breaker if any one of the said plurality of detectors detects an earth leakage in excess of a pre determined level.
21. A differential current transformer having a plurality of primary coils and a secondary coil for sensing current imbalance between the primary coils and wherein the position of the secondary coil relative to the primary coils is adjustable.
22. An earth leakage detector circuit substantially as herein as described for the reference to the accompanying drawings.
23. A differential current transformer substantially as herein as described with the reference to the accompanying drawings.
GB9414931A 1994-02-23 1994-07-25 Earth leakage detection circuit and differential transformer Withdrawn GB2286933A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
TW83107373A TW288103B (en) 1994-02-23 1994-08-12

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB9403463A GB9403463D0 (en) 1994-02-23 1994-02-23 An electrical earth leakage circuit
PCT/SG1995/000001 WO1996026567A1 (en) 1994-02-23 1995-02-23 An earth leakage detector circuit

Publications (2)

Publication Number Publication Date
GB9414931D0 GB9414931D0 (en) 1994-09-14
GB2286933A true GB2286933A (en) 1995-08-30

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GB9403463A Pending GB9403463D0 (en) 1994-02-23 1994-02-23 An electrical earth leakage circuit
GB9414931A Withdrawn GB2286933A (en) 1994-02-23 1994-07-25 Earth leakage detection circuit and differential transformer

Family Applications Before (1)

Application Number Title Priority Date Filing Date
GB9403463A Pending GB9403463D0 (en) 1994-02-23 1994-02-23 An electrical earth leakage circuit

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WO (1) WO1996026567A1 (en)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2370433A (en) * 2000-08-16 2002-06-26 Ford Global Tech Inc Leakage current cancellation device
EP2184827A1 (en) * 2007-07-24 2010-05-12 Panasonic Electric Works Co., Ltd Charge monitoring device

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
RU204520U1 (en) * 2021-04-22 2021-05-28 Евгений Николаевич Коптяев LEAKAGE CURRENT SENSOR
RU206047U1 (en) * 2021-06-12 2021-08-17 Евгений Николаевич Коптяев IMPROVED LEAKAGE CURRENT SENSOR
RU206272U1 (en) * 2021-06-13 2021-09-02 Евгений Николаевич Коптяев LEAKAGE CURRENT SENSOR WITH INCREASED SENSITIVITY

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Publication number Priority date Publication date Assignee Title
GB1448934A (en) * 1973-03-28 1976-09-08 Cutler Hammer Inc Ground fault interrupter
GB1504595A (en) * 1974-04-15 1978-03-22 Rca Corp Ground fault detection apparatus
US3996513A (en) * 1975-04-24 1976-12-07 Butler Fred C Differential microampere current sensor
GB2108339A (en) * 1981-07-07 1983-05-11 Secr Defence Electric protective circuits
GB2178915A (en) * 1985-08-05 1987-02-18 Mk Electric Ltd Power supply apparatus

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2370433A (en) * 2000-08-16 2002-06-26 Ford Global Tech Inc Leakage current cancellation device
GB2370433B (en) * 2000-08-16 2004-12-15 Ford Global Tech Inc Leakage current cancellation device
EP2184827A1 (en) * 2007-07-24 2010-05-12 Panasonic Electric Works Co., Ltd Charge monitoring device
EP2184827A4 (en) * 2007-07-24 2012-11-28 Panasonic Corp Charge monitoring device

Also Published As

Publication number Publication date
WO1996026567A1 (en) 1996-08-29
GB9414931D0 (en) 1994-09-14
GB9403463D0 (en) 1994-04-13

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