What is principle the Murray Loop Test?

A Murray Loop Test is used to locate faults in networks of cables such as three-phase services, groups of underground cables, etc.

It works by using the principle equation on which the Wheatstone bridge is based: when the galvanometer is in a null condition, R1/R3=R2/R4.

The location of a cable fault within a network can be found by using a process of elimination: good connections are identified and are then excluded from further iterations of the Murray Loop Test.