GB2196746A - Earth-fault testing apparatus - Google Patents

Abstract

Apparatus for testing for an earth fault (5a,6a) on either one of two conductors (5,6) comprises two voltmeters (1,2) connected between earth and the ends of the conductors. When the same voltage (v) is applied to both conductors (5,6) any difference in reading between the two voltmeters indicates the presence of an earth fault on one of the conductors. <IMAGE>

Description

SPECIFICATION Electrical testing apparatus The present invention relates to apparatus for testing for the presence of earth faults in electrical conductors.

Conventionally, a single voltmeter with probes is used to test for earth faults in electrical conductors. This type of device is portable, and is not permanently wired into the conductor. This has certain disadvantages in that it is time consuming and inconvenient.

It is therefore the aim of the present invention to provide apparatus for testing for earth faults in electrical conductors which overcomes the above mentioned disadvantages.

According to the present invention there is provided apparatus for testing for the presence of an earth fault on an electrical conductor, the apparatus comprising two voltmeters each connected between earth and the end of a conductor, each of the conductors having applied thereto the same standard voltage, whereby a difference between the readings on the two voltmeters indicates the presence of an earth fault on either one of the conductors.

Preferably the apparatus also includes switch means enabling a number of different conductors to be tested successively.

Preferably, the apparatus also includes an ammeter connected across two of said conductors to measure output current.

The present invention is particularly suited for, though not restricted to, use with multicore electrical cables, such as those used with mining equipment. In this case, each core is individually tested in succession.

The voltmeters may be digital or non-digital, and they may also be centre-reading.

An embodiment of the present invention will now be described by way of example only, with reference to the accompanying drawings in which; Figure 1is a schematic of apparatus according to the present invention Figure is an equivalent circuit of the arrangement shown in Fig. 1.

Referring to Fig. 1, in one embodiment of the present inventiorl, two voltmeters 1,2 are connected in series and earthed at point 3. A standard, positive reference voltage, +v volts is applied to both voltmeters 1 and 2, via conductors 5,6. Voltmeter 1 then reads +v volts.

Voltmeter 2 is connected, via a multi-switch 4, to any one of a number of other conductors 6, for example individual cores of a multicore cable. When there are no earth faults on either conductor 5 or 6, the voltmeter 2 reads the same as voltmeter 1, i.e. +v volts. However, if an earth fault 5a is present on conductor 5, there will be a voltage drop which depends on the resistance of the fault, and then the reading on voltmeter 1 will be lower than that on voltmeter 2. If there is an earth fault 6a on conductor 6, the reading on voltmeter 2 will be lower than that on voltage 1.

In a preferred arrangement, an ammeter can be connected across two adjacent cores to check the output current, the multi-switch 4 rendering the ammeter active wheneit is turned to a certain position.

The whole apparatus is arranged within a box (not shown), and another box (not shown) may be provided with sockets into which all the individual cores of the multi-core cable are plugged, the two boxes being connected together electrically.

1. Apparatus for testing for the presence of an earth fault on an electrcial conductor, the apparatus comprising two voltmeters each connected between earth and the end of a conductor, each of the conductors having applied thereto the same standard voltage, whereby a difference between the readings on the two voltmeters indicates the presence of an earth fault on either one of the conductors.

2. Apparatus according to Claim 1 and including switch means enabling a number of different conductors to be tested successively.

3. Apparatus according to Claim 1 or Claim 2 and including an ammeter connected across two of said conductors to measure output current.

4. Apparatus according to any of the preceding Claims in which the voltmeters are centre-reading.

5. Apparatus according to Claim 1 and substantially as herein described.

6. Apparatus for testing for the presence of an earth fault on an electrical conductor, the apparatus being substantially as herein described with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (6)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Electrical testing apparatus The present invention relates to apparatus for testing for the presence of earth faults in electrical conductors. Conventionally, a single voltmeter with probes is used to test for earth faults in electrical conductors. This type of device is portable, and is not permanently wired into the conductor. This has certain disadvantages in that it is time consuming and inconvenient. It is therefore the aim of the present invention to provide apparatus for testing for earth faults in electrical conductors which overcomes the above mentioned disadvantages. According to the present invention there is provided apparatus for testing for the presence of an earth fault on an electrical conductor, the apparatus comprising two voltmeters each connected between earth and the end of a conductor, each of the conductors having applied thereto the same standard voltage, whereby a difference between the readings on the two voltmeters indicates the presence of an earth fault on either one of the conductors. Preferably the apparatus also includes switch means enabling a number of different conductors to be tested successively. Preferably, the apparatus also includes an ammeter connected across two of said conductors to measure output current. The present invention is particularly suited for, though not restricted to, use with multicore electrical cables, such as those used with mining equipment. In this case, each core is individually tested in succession. The voltmeters may be digital or non-digital, and they may also be centre-reading. An embodiment of the present invention will now be described by way of example only, with reference to the accompanying drawings in which; Figure 1is a schematic of apparatus according to the present invention Figure is an equivalent circuit of the arrangement shown in Fig. 1. Referring to Fig. 1, in one embodiment of the present inventiorl, two voltmeters 1,2 are connected in series and earthed at point 3. A standard, positive reference voltage, +v volts is applied to both voltmeters 1 and 2, via conductors 5,6. Voltmeter 1 then reads +v volts. Voltmeter 2 is connected, via a multi-switch 4, to any one of a number of other conductors 6, for example individual cores of a multicore cable. When there are no earth faults on either conductor 5 or 6, the voltmeter 2 reads the same as voltmeter 1, i.e. +v volts. However, if an earth fault 5a is present on conductor 5, there will be a voltage drop which depends on the resistance of the fault, and then the reading on voltmeter 1 will be lower than that on voltmeter 2. If there is an earth fault 6a on conductor 6, the reading on voltmeter 2 will be lower than that on voltage 1. In a preferred arrangement, an ammeter can be connected across two adjacent cores to check the output current, the multi-switch 4 rendering the ammeter active wheneit is turned to a certain position. The whole apparatus is arranged within a box (not shown), and another box (not shown) may be provided with sockets into which all the individual cores of the multi-core cable are plugged, the two boxes being connected together electrically. CLAIMS

1. Apparatus for testing for the presence of an earth fault on an electrcial conductor, the apparatus comprising two voltmeters each connected between earth and the end of a conductor, each of the conductors having applied thereto the same standard voltage, whereby a difference between the readings on the two voltmeters indicates the presence of an earth fault on either one of the conductors.

2. Apparatus according to Claim 1 and including switch means enabling a number of different conductors to be tested successively.

3. Apparatus according to Claim 1 or Claim 2 and including an ammeter connected across two of said conductors to measure output current.

4. Apparatus according to any of the preceding Claims in which the voltmeters are centre-reading.

5. Apparatus according to Claim 1 and substantially as herein described.

6. Apparatus for testing for the presence of an earth fault on an electrical conductor, the apparatus being substantially as herein described with reference to the accompanying drawings.