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LOCALIZATION OF CABLE FAULT TEST

All the localisation tests normally involves somecalculations of some kind and slide-rule accuracy

is sufficient for tests on short length cables.

Where cables are long, log tables or handcalculations are best for a really accurate pin-

pointing of the fault position.Most common fault in a cable is a fault to earth,

affecting either one or more cores.

Open circuit faults and short circuit faults aremuch less common.

The first step in the fault location procedure is todetermine the characteristic of the fault,

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Murray Loop Test

Murray Loop Test Circuit.

The circuit diagram to locate fault by Murray loop test methodis shown in the figure above ( earth fault ).

P and Q are two ratio arms consisting of resistors, G is a

galvanometer, E is a battery and S1 is a battery key.

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Murray Loop Test

Murray loop for location of ground fault.

A known good conductor is joined to the faulty conductor at aconvenient point beyond the fault but at a known distance from

the test connection.

One terminal of the test battery is grounded.

The resulting Wheatstone bridge is then balanced by adjusting

RB until a null is obtained.

Ratio RA/RB is then known.

For a circuit having a uniform ratio of resistance with length,

circuit resistance is directly proportional to circuit length

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Murray Loop Test

Fig. Murray loop for location of ground fault.

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