GB2376304A

GB2376304A - Electrical Circuit Testing Aid

Info

Publication number: GB2376304A
Application number: GB0207353A
Authority: GB
Inventors: Iain Edward Welch
Original assignee: Individual
Current assignee: Individual
Priority date: 2001-03-30
Filing date: 2002-03-28
Publication date: 2002-12-11
Anticipated expiration: 2022-03-28
Also published as: GB0207353D0; GB2376304B

Abstract

An electrical circuit testing aid, particularly for conducting Earth Loop Impedance Tests and Polarity Tests on circuits for industrial, commercial or domestic buildings, enabling fewer trips between each circuit outlet and its power distribution board. The testing aid 30 comprises a remotely controllable 2-way switch 32 allowing either output terminal of the switch 42 or 46 to be connected to input terminal 36. A remote controller 34 controls the switch by means of an aerial signal, such as a 433 MHz radio wave. With the switch connecting outgoing live wire 16 to earth terminal 21 (terminals 36 and 42 connected) an R1 test is performed, and a Polarity test is performed at a circuit outlet using continuity tester 28. The switch is then operated to connect for normal circuit operation (terminals 36, 46 connected), and Earth Loop Impedance test is performed on the live circuit at the outlet.

Description

Electrical Circuit Testing Aid The present invention relates to an electrical circuit testing aid and more particularly, but not exclusively, to an electrical circuit testing aid for use in the testing of electrical installations in domestic, commercial and industrial buildings.

Electricians are regularly required to carry out two types oftest on electrical installations in the United Kingdom. The first test, called the Earth Loop Impedance Test, is carried out at an electrical outlet positioned at the furthest point in a circuit from its power supply, for example a distribution or fuse board, whilst the circuit is live. An instrument, commonly known as an earth loop impedance tester is connected across the live, neutral and earth terminals ofthe outlet, and is used to measure the earth loop fault. The earth loop fault is the electrical resistance ofthe earth wire from the point of test, ie the outlet, to the power supply, and back to the point oftest via the live wire. The resistance measurement is recorded, and should fall within statutory limits for continued safe use of the circuit.

The second test is called the Polarity Test or Rl and R2 Test, and is also carried out at an electrical outlet positioned at the furthest point in a circuit from its power source, i. e. the distribution board.

The power supply is disconnected form the circuit being tested and a conductive link is fitted between the live and earth wires of the circuit. In practice, this is achieved by connecting a link between the live and earth terminals at the distribution board. A continuity tester, more commonly known as a megger, is used to measure the resistance ofthe connected live and earth wires from the electrical outlet. As with the Earth Loop Impedance Test, the resistance measurement is recorded, and should fall within statutory limits for continued safe use ofthe circuit. After taking the test, the link is removed from the terminals of the distribution board, and the power supply to the circuit is re-connected.

Currently, it is time consuming for an electrician to carry out both the Earth Loop Impedance Test and the Polarity Test on one or a number of circuits supplied from a distribution board in a building.

For example, when testing a lighting circuit, firstly for the Earth Loop Impedance Test, the electrician dismantles the light fitting positioned in the circuit at the furthest point from the distribution board while the circuit is live. He then measures the earth loop impedance as described above.

Then, secondly, for the Polarity Test, the electrician must walk to the distribution board, turn off the circuit being tested, and fit a temporary conductive link between the live and earth terminals of the distribution board as described above. He then walks back to the test position at the light fitting and measures the resistance ofthe live and earth wires as described above. After testing, he reassembles the light fitting, walks back to the distribution board, removes the temporary link and switches the power supply to the lighting circuit back on.

Therefore, if the electrician is at the distribution board, he must walk to the point of test for the Earth Loop Impedance Test, back from the point of test to the distribution board in order to turn o ffthe power supply and fit a temporary conductive link for the Polarity Test, back to the point of test to carry out the Polarity Test, and finally back to the distribution board in order to remove the temporary link and turn the power supply back on.

According to the broadest aspect of the present invention there is provided an electrical circuit testing aid comprising a remotely controllable switch, first, second and third leads connected to the switch for connection to a circuit to be tested, and a remote controller for controlling the switch by means of an aerial signal.

It is an advantage of the invention that when the electrical circuit testing aid is connected to an outgoing live supply wire of a circuit, and to the live and earth terminal of a distribution board, then an electrician does not have to walk back to the distribution board from a test position m the circuit in order to carry out both an Earth Loop Impedance Test and a Polarity Test.

The aerial signal is a preferably a radio wave having a frequency of substantially 433 MHz.

Preferably, the switch is a 2-way switch. The switch maybe provided by a pair of sequentially

switching relays.

A fourth lead may be provided, the third and forth leads being adapted to connect to the live and neutral terminals of a power supply for powering the testing aid.

Preferably, the first lead is connected to the input terminal ofthe 2-way switch and is adapted to connect to a wire of a circuit to be tested, the second lead is connected to a first output terminal of the 2-way switch and is adapted to connect to an earth terminal ofthe power supply, and the third lead is connected to a second output terminal of the 2-way switch.

The terminals of the power supply are preferably arranged on a distribution board.

Preferably, at least one fuse is provided for overload protection. The fuse may be an electronic fuse and/or a cartridge fuse.

A timer circuit is preferably provided for bypassing the or each fuse for a given period oftime.

Conveniently, the timer circuit may be set to bypass the or each fuse for up to between 5 and 6 seconds from when power is supplied to the testing aid.

Preferably, a warning light is provided, which indicates when the fuse has been overloaded.

The present invention also provides a method of conducting an Earth Loop Impedance Test and a Polarity Test on a circuit using an electrical circuit testing aid having first, second and third leads connected to a switch for connection to a circuit to be tested, comprising the steps of : connecting a first lead of the testing aid to a circuit's outgoing live supply wire having been disconnected from a live terminal of a distribution board, connecting a second lead of the testing aid to an earth terminal of the distribution board, and connecting a third lead to a live terminal of the distribution board, operating a remote controller, for controlling the switch by means of an aerial signal, the switch being controlled to connect the first and second leads thus making a conductive link between the outgoing live supply wire and the earth terminal of the distribution board, conducting a Polarity

Test using a continuity tester at an outlet in the circuit, operating the remote controller to throw the switch thus connecting the outgoing live supply wire to the live terminal of the distribution board as in the usual operation of the circuit, and conducting an Earth Loop Impedance Test at the outlet using an earth loop impedance tester.

The invention will now be described byway of example onlywith reference to Figs 1 to 5B ofthe accompanying drawings in which ; Fig 1 shows a diagrammatic view of an electrical circuit including an outlet connected to a distribution board by live, neutral and earth wires and being conventionally tested by an earth loop impedance tester; Fig 2 shows a diagrammatic view ofthe electrical circuit of Fig 1 with a temporary link in the distribution board and being conventionally tested by a continuity tester; Fig 3 shows a diagrammatic view of an electrical circuit testing aid according to the invention, connected to the electrical circuit as shown in Figs 1 and 2; Fig 4 shows a diagrammatic view of a switch of the electrical circuit testing aid; Fig 5 shows a diagrammatic view ofthe switch of Fig 4 consisting of a pair of relays in a first position; Fig 5A shows a diagrammatic view of the switch of Fig 5 with the relays in a second position; Fig 5B shows a diagrammatic view of the switch of Fig 5 with the relays in a third position; Figure 6 is a schematic diagram of a remote controller of the testing aid of Figure 3; Figure 7 is a detailed schematic diagram of a practical form of base station of the testing aid

of Figure 3; Fig 8 is a view similar to that of Figure 5 ofthe switch of Figure 7 consisting of a pair of relays in a first position; Fig 8A shows a diagrammatic view of the switch of Fig 8 with the relays in a second position; Fig 8B shows a diagrammatic view of the switch of Fig 8 with the relays in a third position; Referring firstlyto Fig 1, an electrical circuit is indicated generally at 10, and comprises a light fitting 12 connected to a distribution board 14 with live, neutral and earth wires, referenced 16,18, 20 respectively. The distribution board has live, neutral and earth terminals referenced 17, 19 and 21 respectively. A switch 22 is connected in the live wire 16 in the manner of a conventional domestic lighting circuit. An earth loop impedance tester 24 is connected to live, neutral and earth terminals of the light fitting 12 in order to take an Earth Loop Impedance Test in conventional manner with the power supply to the circuit 10 switched on.

Referring now to Fig 2, the electrical circuit 10 of Fig 1 is shown with a temporary conductive link

26, eg a length of insulated wire, connecting the live terminal 17 and the earth terminal 21 ofthe distribution board 14. The power supply to the circuit 10 is switched off. A continuity tester 28 is connected to the live and earth terminals of the light fitting 12 in order to take a Polarity Test, or R1 andR2 Test, in conventional manner. After taking ofthe test, the temporary link 26 is removed from the circuit 10 and the power supply switched back on.

The invention will now be described with reference to Fig 3. Common reference numerals will be used to indicate parts of me lighting circuit 10 in common with the parts shown in Figs 1 and 2. An electrical circuit testing aid is indicated generally at 30 and comprises a 2-way switch shown diagrammatically at 32, which is operable by a remote controller 34, and is mounted on a base station 31.

A first output terminal 42 of the switch 32 is connected to a first or earth lead 44, which is connected to the earth terminal 21 of the distribution board 14. The second output terminal 46 of the switch 32 is connected to a second or live lead 48, which is connected to the live terminal 17 of the distribution board 14. The second output terminal 46 is also connected to electronics ofthe testing aid, indicated schematically at 50. A third or neutral lead 52 is also connected to the electronics 50, azid is connected to theneutral terminal 19 ofthe distributionboard 14. Therefore electrical power is supplied to the electronics 50 through the live and neutral leads 48,52 from the live and neutral terminals 17,19 of the distribution board 14.

An input terminal 36 ofthe switch 32 is connected to athird of load lead 38 having a connector 40, at its distal end. In use, the connector 40 is connected to the end of the live wire 16, which has been disconnected from the live terminal 17 ofthe distribution board 14. An internal transformer (not shown) reduces the supply voltage to a suitable level, for example between 6 and 12 volts, and the supply is subsequently conditioned from AC to DC by rectification.

The switch 32 is provided by a pair of sequentially switching relays 66,68, shown schematically in Fig. 5. The first relay 66 switches the first output terminal 42 (connected to earth), to the input terminal 3 6 (connected to the outgoing load wire 16). The second relay 68 switches the second output terminal 46 (connected by the live wire 48to the live terminal 17 ofthe distribution board), to the input terminal 36. On receiving a signal to switch, the first relay 66 switches to the position shown in Fig 5A, with neither ofthe terminals 42,46 being connected to the output terminal 36. After a short time delay, for example 0.5 seconds, the second relay 68 switches to the position shown in Fig 5B, thus connecting the terminal 46 to the terminal 36.

When the relays 66,68 receive a signal to switch back to the position shown in Fig 5, the second relay 68 switches first, followed by the first relay 66. The use of two relays 66,68 minimises the risk of arcing from the live terminal 46.

The ends of the earth, live, load and neutral leads 44, 48, 38 and 52 are connected to the pins of a 4-pin plug respectively (not shown), which locates i : : a socket (not shown) provided in the end ofthe base station 31. The socket and plug are arranged to prevent incorrect connection of the

leads 44,48, 38 and 52, with the socket only being capable of receiving the plug in one orientation.

When the plug is located in the socket, a rotary lock retains the plug in the connected position.

The other end of the live lead 48 is provided with a short electrically conducting pin, which can easily be inserted into and clamped by a screw of the live terminal 17 of the distribution board 14.

The connector 40 at the end of the load lead 38 is an insulated connector block having a spring loaded cable clamp, for ease of connection o the disconnected tail of the circuit's outgoing live wire 16. The earth lead 44 has a spring clip, for example a crocodile clip, at its end for ease of connection to the earth terminal 21 of the distribution board, and the neutral lead 52 has an Insulated spring clip, for example an insulated crocodile clip, at its end for ease of connection to the neutral terminal 19 of the distribution board. The leads 44,48, 38 and 52 are colour coded for added ease of identification.

The base station 31 is provided with an electronic fuse (not shown), including an internal current sensor for overload protection of the testing aid 30, which checks the load on the outgoing live lead 38. The sensor is positioned in the connection between the input terminal 36 of the switch 32, and the plug and socket connection to the load lead 38 of the testing aid 30. If the load exceeds 5.8 amps, then the connection is broken, an overload lamp 100 will illuminate, and a warning buzzer 102 will sound until the power supply to the base station is switched off or disconnected. An internal cartridge fuse (not shown) is also provided, which adds further protection. The cartridge fuse is rated at 6 amps.

A timer circuit is also provided in the connection between the input terminal 36 of the switch 32, and the plug and socket connection to the load lead 38, which is capable of bypassing the electronic and cartridge fuse for a given period oftime. Typically, the timer circuit may be set to bypass the fuses for up to between 5 and 6 seconds from when power is supplied to the testing aid.

This bypass is necessary when testing a fluorescent light fitting, because of the voltage surge from the starting capacitor of the light fitting, which is required to start the fluorescent light when first

turned on. Such a voltage surge causes a surge of current through the testing apparatus, which would at least trip the electronic fuse, if not bypassed. The bypass can also be used when testing other electrical circuits which have an increased starting voltage.

If the base station 31 is overloaded, then usually the electronic fuse will trip before the cartridge fuse blows, and therefore the electronic fuse can simply be reset. Otherwise, if the cartridge fuse is overloaded, it must be replaced. The base unit 3 i is also provided with a Polarity Test indication light 62, an Rl indicator light 60 (described below), and an Earth Loop Impedance Test light 64.

The remote controller 34 has two test push buttons 54,56, an indicator light 58, and is powered by an internal 6-volt battery 80. The remote controller 34 also has an address select switch panel 82, an encoder integrated circuit 84 and a transmitter module 86 for transmitting a signal to the base station. The address select switch panel 82 allows a pre-selected code to be applied to the encoder integrated circuit 84 by suitable selection ofthe positions ofthe switches on the panel. In Figure 6, the illustrated example code is 2567.

Pressing each ofthe switches 54, 5 6 also generates a signal unique to that switch and that signal, together with the code are encoded by the integrated circuit 84 and applied to the transmitter module 86 for transmission to the base station. The remote controller 34 operates using a one-way radio link at approximately 433 MHz, indicated at 70 in Fig 3, which is transmitted from the remote controller to the base station 31. If either of the test push buttons 54,56 is depressed, the indicator light 5 8 illuminates, which indicates that the remote controller 34 is transmitting correctly, and that the battery is not flat. The power required for each transmission is low, and it is expected that the battery will have a reasonably long life, for example at least 6 months if used daily.

In operation, two sequential radio signals are transmitted to the base station 31, one being the code 2567 in this example, when either of the test push buttons 54,56 are depressed. The remote controller 34 and base station 31 are preset to the same frequency, which is unique to that apparatus. A receiver 88 in the base station 31 receives and confirms that both ofthe signals are ofthe correct frequency, and if so, subsequently operates the switch 32 through the electronics 50

in the manner signalled by the remote controller.

Figures 6,7 and 8 to 8B show in detail a practical embodiment of the invention.

The receiver 88 has a receiver module 90 which receives the signal from the remote controller 34 and applies it to a decoder integrated circuit 92. The decoder 92 checks the received code against a code applied from an address select switch panel 94, in which the various switches have been set to duplicate the code ofthe remote controller 34. In this example the code is 2567. The output of the decoder 92 is then applied to a microprocessor 94, which controls the lights 62,64 in the form ofligm omitting diodes and the R1 indicator light 60, also a light omitting diode, and light omitting diodes 98,100, together with an audible warning device 102.

The operation of the electrical circuit testing aid 30 will now be described, with reference in

particular to Figs 3 and 4. Firstly, the power supply is switched off at the distribution board 14 and the leads 44, 48, 38 and 52 of the base station 31 are connected to the circuit 10 as described above. Thus, the load lead 38 is connected to the outgoing live wire 16, the earth lead 44 to the earth terminal 21, the live lead 48 to the live terminal 17, and the neutral lead 52 to the neutral terminal 19. The effect of the connections is that either the circuit 10 is connected for normal operation, with the terminals 36, 46 of the switch connected together by the contact 33, or the outgoing live wire 16 and the earth terminal 21 are connected by use of the load and earth leads 3 8, 44.

In the first instance, the contact 33 ofthe switch 32 is positioned such that the input terminal 36 is connected to the output terminal 42, that is, with the outgoing live wire 16 and earth wire 20

electrically connected (Figs 3 and 5). The power supply is then switched back on.

1. 2 When the power supply is switched on, the base station 31 immediately checks the outgoing live wire 16 (using the opto coupler 63), via load lead 3 8, for a voltage. This is known as an Rl test.

Should this wire 16 already be live, lion the tester 30 will not allow any further tests, the Rl indicator light 60 illuminates, and the warning buzzer 102 sounds until the power is switched offor

disconnected. The wire 16 is sometimes live, for example, because the wire is part of a ring main, and the other end of the ring main is connected to the distribution board 14 and is still live.

For the short circuit test, once the R1 test has been completed, the base station 31 measures the resistance between the outgoing live wire 16 and the earth terminal 21. If the resistance measured is less than 0.5 ohms, then the base station 31 determines that there is a short circuit between the outgoing live wire 16 and the earth terminal 21, the tester 3 0 will not allow any further tests, the short circuit indicator light 98 illuminates, and the warning buzzer 102 sounds until the power is switched off or disconnected. A short circuit is typically caused by a fault in the cable between the distribution board 14 and the outlet 12.

Once the RI test and the short circuit test have been completed, the electrician then walks to the furthest point in the circuit, in this case the light fitting 12. He dismantles the light fitting 12 and takes a Polarity Test in conventional manner using a continuity tester 28 as described above.

The electrician then presses the push button 54 ofthe remote controller 34, and the contact 33 of the switch 32 is thrown to the position shown in Figs 4 and 5B and Fig 8B, that is, with the input terminal 36 connected to the output terminal 46. This is effected by the sequence shown in Figs 5,5A and 5B as described above and Figs 8,8A and 8B. In this position, the live wire 16 is connected to the live terminal 17 of the distribution board, as in the usual operation ofthe circuit. The earth loop impedance tester 24, see Fig 1, can then be connected to the terminals ofthe light fitting 12 and an Earth Loop Impedance Test effected in the conventional manner.

After taking the Earth Loop Impedance Test, the electrician presses the push button 56, which returns the contact 33 of'. he switch 32 to its original position, that is, between terminals 3 6 and 42. He then re-assembles the light fitting 12, walks back to the distribution board 14, and disconnects the leads 44,48, 38 and 52, and reconnects the live wire 16 with the live terminal 17 of the distribution board 14.

Therefore, in order to take both the Polarity Test and Earth Loop Impedance Test, the electrician

only has to walk from the distribution board 14 to the light fitting 12, and back again, when using the electrical circuit testing aid of the invention. In large buildings, the furthest outlet in each electrical circuit may be a large distance from its respective power distribution board, and consequently by reducing the number of trips required between each outlet and its power distribution board, large time savings can be made. These time savings result in lower cost testing of circuits.

When the testing aid is in use, the electronic fuse constantly monitors current passing through the base station 31 to the outgoing live wire 16. If the current exceeds 5.8 amps, for example, due to a person other than the tester turning on a large load on the circuit, then the base station will shut down as described above.

Claims

CLAIMS 1. An electrical circuit testing aid comprising a remotely controllable switch, first, second and third leads connected to the switch for connection to a circuit to be tested, and a remote controller for controlling the switch by means of an aerial signal.
2. An electrical circuit testing aid as claimed in claim 1, in which the aerial signal is a radio wave having a frequency of substantially 433 MHz.
3. An electrical circuit testing aid as claimed in claim 1 or claim 2, in which the switch is a 2- way switch.
4. An electrical circuit testing aid as claimed any of claims 1 to 3, in which the switch comprisesa pair of sequentially switching relays.
5. An electrical circuit testing aid as claimed in any of claims 1 to 4, in which a fourth lead is provided, the third and fourth leads being adapted to connect to the live and neutral terminals of a power supply for powering the testing aid.
6. An electrical circuit testing aid as claimed in claim 5, in which the first lead is connected to the input terminal of the 2-way switch and is adapted to connect to a wire of a circuit to be tested, the second lead is connected to a first output terminal ofthe 2-way switch and is adapted to connect to an earth terminal of the power supply, and the third lead is connected to a second output terminal of the 2-way switch.
7. An electrical circuit testing aid as claimed in claim 5, in which the terminals of the power supply are arranged on a distribution board.

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8. An electrical circuit testing aid as claimed in any one of claims 5 to 7 in which the first, second, third and fourth leads are connected to a base station of the testing aid by a four pin plug.
9. An electrical circuit testing aid as claimed in any preceding claim, in which at least one fuse is provided for overload protection.
10. An electrical circuit testing aid as claimed in anypreceding claim, in which an electronic fuse is provided for overload protection.
11. An electrical circuit testing aid as claimed in any preceding claim, in which a cartridge fuse is provided for overload protection.
12. An electrical circuit testing aid as claimed in any one of claims 9 to 11, in which a timer circuit is provided, which bypasses the or each fuse for a given period of time.
13. An electrical circuit testing aid as claimed in claim 12, in which the timer circuit is set to bypass the or each fuse for up to between 5 and 6 seconds from when power is supplied to the testing aid.
14. An electrical circuit testing aid as claimed in any of claims 9 to 13, in which a warning light is provided, which indicates when the or each fuse has been overloaded.
15. A method of conducting an Earth Loop Impedance Test and a Polarity Test on a circuit using an electrical circuit testing aid having first, second and third leads connected to the switch for connection to a circuit to be tested, comprising the steps of ; connecting a first lead ofthe testing aid to a circuit's outgoing live supply wire having been disconnected from the live terminal of a distribution board, connecting a second lead of the testing aid to an earth terminal ofthe distribution board, and

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connecting a third lead to a live terminal of the distribution board, operating a remote controller, for controlling the switch by means of an aerial signal, to ensure that the switch connects the first and second leads thus making a conductive link between the outgoing live supply wire and the earth terminal of the distribution board, conducting a Polarity Test using a continuity tester at an outlet in the circuit, operating the remote controller to throw the switch thus connecting the outgoing live supply wire to the live terminal of the distribution board as in the usual operation of the circuit, and conducting an Earth Loop Impedance Test at the outlet using an earth loop impedance tester.
16. An electrical circuit testing aid substantially as described herein with reference to and as illustrated in Figs 3,4, SA, 5B, 5C, 6,7 and 8 to 8B of the accompanying drawings.
17. A method of conducting an Earth Loop Impedance Test and aPoiarityTest substantially as described herein with reference to and as illustrated in Figs 3,4, 5A, 5B, 5C, 6,7 and 8 to 8B of the accompanying drawings.