Apparatus for insulation resistance testing of an electrical circuit

Abstract

A device for insulation resistance testing of an electrical circuit, the device comprising a pair of electrical cables (12, 14), each cable being communicably coupled at one end to a connector (18a, 18b) configured, in use, to be connected to an output of an RCBO breaker (24) associated with said electrical circuit, and configured at its opposite end to be connected, in use, to the test lead (22) of a Megohmmeter, the device further comprising a permanent magnet located in each said electrical cable (12, 14) between a respective connector (18a, 18b) and said opposite end, the device being configured such that each said electrical cable (12, 14), in use, creates an electrical connection between said RCBO breaker output and said Megohmmeter, through said respective permanent magnet, when the respective connector (18a, 18b) is connected to a respective output of said RCBO breaker (24) and said electrical cable is connected at the opposite end to a said Megohmmeter.

Description

[0001] APPARATUS FOR INSULATION RESISTANCE TESTING OF AN ELECTRICAL

[0002] CIRCUIT

[0003] Field of the Invention

[0004] This invention relates generally to an apparatus for insulation resistance testing of an electrical circuit and, more particularly but not necessarily exclusively, to an apparatus and method for insulation resistance testing in a new electrical installation.

[0005] Background of the Invention

[0006] Insulation resistance testing is an essential procedure used to assess the effectiveness of insulation surrounding electrical conductors such as cables. Insulation resistance refers to the measured value in Ohms of the insulating material surrounding electrical conductors. When electric current flows through conductors, it can either pass directly through the insulator material or around its surface, and the amount of current flow depends on the magnitude and nature of voltages being used. Adequate insulation between conductors and other surrounding objects is crucial to prevent problems such as short circuits, flash arcing, overheating, fire and electrocution.

[0007] An insulation tester (also knowns as a Megohmmeter) is used for this purpose. The principle involves applying a known DC voltage to the conductor and measuring the resulting current flow. The voltage across a conductor is directly proportional to the current flowing through it (assuming physical conditions and temperatures remain constant).

[0008] A Megohmmeter is made up of combining a series-type ohmmeter and a DC generator. More specifically, two coils, V1 and V2, and one current coil constitute a Megohmmeter. The electric current drawn by the circuit under test would pass through a deflecting coil or current coil connected in series.

[0009] Accordingly, a Megohmmeter has two terminals and resistance is measured across the terminals, i.e. connected in series with the deflecting coil and across the (DC voltage) generator. When current is supplied to the coils, then they have torque in opposite directions. A pointer is provided to indicate the measured resistance, and acceptable resistance values are typically 1 to 10 Megaohms, depending on the standards referenced.

[0010] In general, the first step when using a Megohmmeter, is to remove all power from the wires or circuit to be tested. Next, it is necessary to uninstall all wires that are to b tested. One of the Megohmmeter’s terminals is connected to a first element of the system (depending on the installation being tested), and the other of the Megohmmeter’s terminals is connected to another element of the system, such that the deflecting coil can provide a reading via the pointer.

[0011] Historically, in a domestic or even industrial a system installation process, Insulation Resistance testing of a circuit on a new installation is carried out in three steps;

[0012] Step 1 : Line to Neutral

[0013] Step 2: Line to Earth

[0014] Step 3: Neutral to Earth

[0015] Thus, on a single phase system, in step 1 , the line (Brown) conductor is tested against the neutral (Blue) conductor; in step 2, the line conductor is tested against the CPC (earthing conductor), and in step 3, the Neutral is tested against the CPC. Tis process is illustrated schematically in Figure 1 of the drawings.

[0016] In recent years, there has been an increase in the installation of accessories that influence Insulation Regulation readings during testing; accessories such as sockets with integrated USB chargers and LED lighting being among the most common. These accessories are also susceptible to damage during Insulation Resistance testing of Line to Neutral if precautions are not taken,

[0017] As is impractical to remove these types of accessories after installation, for testing, Guidance Note 3 was issued in relation to the IET Wiring Regulations, which provides an alternative test method which eliminates the need to test Line to Neutral. Said Guidance Note 3 is provided below for reference:

[0018] Thus, and as indicate above, the second stage of such Insulation Resistance testing requires the Line and Neutral conductors to be connected together and tested against the CPC (earthing conductor). The image illustrated in Figure 2 of the drawings, derived from NAPIT, shows the conductors being removed and linked for this purpose.

[0019] It will be evident that this process would be very time consuming for an electrician, and also potentially frustrating after they have spent a significant amount of time dressing the board neatly.

[0020] Aspects of the present invention seek to address at least one or more of these issues. Statements of Invention

[0021] According to a first aspect of the invention, there is provided a device for insulation resistance testing of an electrical circuit, the device comprising a pair of electrical cables, each cable being communicably coupled at one end to a connector configured, in use, to be connected to an output of an RCBO breaker associated with said electrical circuit, and configured at its opposite end to be connected, in use, to the test lead of a

[0022] Megohmmeter, the device further comprising a permanent magnet located in each said electrical cable between a respective connector and said opposite end, the device being configured such that each said electrical cable, in use, creates an electrical connection between said RCBO breaker output and said Megohmmeter, through said respective permanent magnet, when the respective connector is connected to a respective output of said RCBO breaker and said electrical cable is connected at the opposite end to a said Megohmmeter.

[0023] In an embodiment, the device may comprise a housing having, at one end, connection means for connecting the housing to a test lead of a Megohmmeter, the proximal ends of said electrical cables being housed within said housing and electrically insulated from each other therein, and being coupled to a respective connection means. The housing is beneficially formed of a non conductive plastics material, such as polyvinylchloride.

[0024] In an embodiment, each electrical cable may comprise a wire of highly conductive material, such as copper, covered in a non conductive material, such as butyronitrile.

[0025] Beneficially, each cable may comprise, at its distal end, a casing within which said permanent magnet is housed, and from which a respective connector extends, each said connector being coupled to a respective permanent magnet. Advantageously, each casing may be formed of a non conductive material, such as polyvinylchloride.

[0026] In an embodiment, each said permanent magnet may comprise a rare-earth magnet.

[0027] Advantageously, at least one (and preferably both) of said permanent magnets may be formed of neodymium.

[0028] These and other aspects of the invention will become apparent from the following detailed description.

[0029] Brief Description of the Drawings

[0030] Embodiments of the invention will now be described, by way of examples only, and with reference to the accompanying drawings, in which:

[0031] Figure 1 is a schematic illustration of a Megohmmeter in use in an insulation resistance test of a final circuit, in accordance with the prior art;

[0032] Figure 2 is a schematic illustration of an Insulation Resistance testing method with a 250V DC test voltage showing the line and neutral conductors connected together, in accordance with the prior art; Figure 3 is a schematic diagram illustrating a device according to an exemplary embodiment of the invention, in use when performing an IR test in relation to a RCBO; and

[0033] Figure 3A is schematic diagram illustrating the housing of the device of Figure 3 connected to a conventional test lead of a Megohmmeter.

[0034] Detailed Description

[0035] In the following description of various exemplary embodiments of the invention, reference is made to the accompanying drawings that form a part hereof, and in which are shown, by way of examples and illustration, specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that variations and modifications may be made, without departing from the scope of the invention as defined in the appended claims. The following detailed description is therefore not to be taken in a limited sense.

[0036] The specification may refer to “an”, “one” or “some” embodiment(s) in some parts. This does not necessarily imply that each such reference is to the same embodiment(s), or that the feature applies to only one embodiment. Single features of different embodiments may also be combined to make another embodiment.

[0037] As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless expressly stated otherwise. It will be further understood that the terms “includes”, “comprises”, “including” and / or “comprising”, when used in this specification, specify the presence of stated features, integers, steps, operations, elements and / or components, but do not preclude the presence or addition of one or more other features, integers, operations, steps, elements, components and / or groups thereof As used herein, the term “and / or” includes any and all combinations and arrangements of one or more of the associated listed items.

[0038] Directional descriptors such as upper, lower, left, right, clockwise, anti-clockwise, front, rear and other similar adjectives are used for clarity and refer to the orientation of the invention as illustrated in the drawings, however it will be clear to those skilled in the art that the invention may not always be oriented as illustrated and the invention is not intended to be limited in this regard.

[0039] Aspects of the invention seek to make the statutory insulation resistance testing and, specifically, the second part of the testing process set out in Guidance Note 3 of the IET Wiring Regulations, much quicker and easier by offering an alternative method to link together the live conductors (Line and Neutral) without taking them out of an RCBO (Residual Current Breaker with Over-Current) orAFDD (Arc Fault Detection Device).

[0040] Referring now to Figure 3 of the drawings, there is provided a device for use in insulation resistance testing that mitigates at least one or more of the issues described above in relation to the prior art.

[0041] The illustrated IR testing device of Figure 3 comprises a lead connector 10 formed of, for example PVC or other non-conductive material. First and second cables 12, 14 extend from the lead connector 10. Within the body of the lead connector, the first and second cables 12, 14 are electrically insulated from each other. The first and second cables 12, 14 may comprise copper wire, for example, coated with a non-conductive material such as butyronitrile or the like. Alternative suitable materials will be apparent to a person skilled in the art.

[0042] At the end of each of the first and second cables 12, 14, there is provided a respective generally cylindrical housing 16a, 16b. Wthin each said housing 16a, 16b, there is provided a super strong permanent magnet, for example, a neodymium magnet, electrically connected to the (e.g. copper) wire within the respective cable 12, 14. The proximal ends of the (e.g. copper) wires within each cable are connected (within the lead connector) to a conventional connector 22 for connection to a Megohmmeter.

[0043] At the distal end of each cable 12, 14, adjacent the distal end of each respective cylindrical housing 16a, 16b, which may again be formed of, for example, PVC or similar non conductive material, there is provided a respective connector 18a, 18b configured to be connected to a respective conventional load connection point 20a, 20b of a RCBO breaker 24 found in most fuse boards. The connectors 18a, 18b may, for example, be formed of steel, e.g. ASTM1214 steel, although this may not be essential and alternatives may be envisaged, especially as Regulations move on and change. By connecting a cable 12, 14, via the respective connector 18a, 18b, to the correct load connection point 20a, 20b of a RCBO breaker 24, a connection is made to the magnet and, through the magnet, to the Megohmmeter connected, via its conventional lead 22, to the proximal end of the lead connector 10 (as illustrated in Figure 3A of the drawings).

[0044] As a result, it is possible to connect the line and neutral of an RCBO breaker to a single test lead without the need to remove conductors from the RCBO. The device facilitates testing in line with the latest BS7671 requirements, saves time during testing, eliminates the risk of damaging connections and speeds up EICRs.

[0045] It will be apparent to a person skilled in the art, from the foregoing description, that modifications and variations can be made to the described embodiments without departing from the scope of the invention as defined by the appended claims.

Claims

CLAIMS1 . A device for insulation resistance testing of an electrical circuit, the device comprising a pair of electrical cables, each cable being communicably coupled at one end to a connector configured, in use, to be connected to an output of an RCBO breaker associated with said electrical circuit, and configured at its opposite end to be connected, in use, to the test lead of a Megohmmeter, the device further comprising a permanent magnet located in each said electrical cable between a respective connector and said opposite end, the device being configured such that each said electrical cable, in use, creates an electrical connection between said RCBO breaker output and said Megohmmeter, through said respective permanent magnet, when the respective connector is connected to a respective output of said RCBO breaker and said electrical cable is connected at the opposite end to a said Megohmmeter.

2. A device according to claim 1 , comprising a housing having, at one end, connection means for connecting the housing to a test lead of a Megohmmeter, the proximal ends of said electrical cables being housed within said housing and electrically insulated from each other therein, and being coupled to a respective connection means.

3. A device according to claim 2, wherein said housing is formed of a non conductive plastics material, such as polyvinylchloride.

4. A device according to any of the preceding claims, wherein each electrical cable comprises a wire of highly conductive material, such as copper, covered in a non conductive material, such as butyronitrile.

5. A device according to any of the preceding claims, wherein each cable comprises, at its distal end, a casing within which said permanent magnet is housed, and from which a respective connector extends, each said connector being coupled to a respective permanent magnet.

6. A device according to claim 5, wherein said casing is formed of a non conductive material, such as polyvinylchloride.

7. A device according to any of the preceding claims, wherein each said permanent magnet comprises a rare-earth magnet.

8. A device according to claim 7, wherein at least one of said permanent magnets is formed of neodymium.

9. A device according to claim 8, wherein each permanent magnet is formed of neodymium.

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