5762 High Resistance Fault Locator.
The High Resistance Fault Locator, Type 5762, utilizes a conventional Wheatstone Bridge circuit in which the two sections of the faulted conductor, one on each side of the fault, comprise the two external 
arms of the bridge. 

Introduction

The other two arms of the bridge are 
contained in the instrument.
 
By use of a detector circuit, of extremely 
high input resistance it is possible to locate
high resistance faults without loss of sensitivity. 

With this bridge arrangement, faults having resistance from zero up to 200 MΩ in dielectrics such as rubber and polythene, can be located with an accuracy to well within ±0.5%, a typical error being 6” in 500 feet (150mm in 150m) or ±0.1%. The limitation is determined by the uniformity of the conductor.

Accuracy

Well within ±0.5%, a typical error being 6” in 500 feet (150mm in 150m) or ±0.1%.

Connection Methods

a. WHEN BOTH ENDS OF THE FAULTED CONDUCTOR ARE TOGETHER, as in cable manufacture, or when the cable is on a cable reel. (Fig I and Fig.2)

b. WHEN THE ENDS OF THE FAULTED CONDUCTOR ARE NOT AVAILABLE AT THE SAME POINT, as in the case of a cable in service.

Two methods may be used. The preferred method is to run out two insulated wires to the distant end to serve as current and potential leads. The resistance of these leads should be as low as possible, e.g. less than I Ohm. Alternatively, a good conductor in the cable may be used. Connect the good conductor and the faulted conductor solidly together at the distant end and adequately insulate the joint from earth. Make connections at the near end as shown in Fig.3.

Fault Location 

i) With all the connections made as in (2) switch on the fault locator and allow the instrument to settle for one minute.

ii) By means of the zero control adjust the instrument until the microammeter reads zero.

iii) Connect the second current lead to the battery.

iv) Adjust the Fault Locator main dial for zero reading on the microammeter.

The reading of the main dial then indicates the location of the fault as a percentage of the total length of cable loop from the end connected to the “+“ terminal on the instrument.

v) Reverse the connections to the conductor terminals and rebalance. The sum of the readings obtained in (iv) and (v) should add to 100%.

Note:

The total length of the cable loop means the total length of cable between the potential points, that is the points at which the leads to the terminals of the instrument are connected to the cable. 
This is equal to the length of the cable in the case shown in Figs I and 2 but is equal to twice the length of cable in the case shown in Fig. 3.