Insulation Resistance of a System Interview Questions and Answers:

1. What are the faults that are likely to occur in cables ?

Ans. The faults which are likely to occur in cables are open circuit, short circuit and ground faults.

2. What is meant by ‘ground fault’ in cables ?

Ans. When the current starts flowing from core to earth or to cable sheath because of damage to the cable insulation, the fault is known as ground or earth fault.

3. What is meant by ‘short-circuit’ fault in cables ?

Ans. When the current starts flowing from one cable to another cable or from one core to another core of a multi-core cable due to damage to the cable insulation, the fault is called the cross or short-circuit fault.

4. What is meant by ‘open-circuit fault’ in cables ?

Ans. When the conductor of a cable is broken or joint is pulled out, the fault is called the open-circuit fault.

5. What principle do Murray loop and Varley loop tests employ ?

Ans. Murray loop and Varley loop tests employ the principle of Wheatstone bridge.

6. What is the essential difference between Murray and Varley loop tests ?

Ans. The difference between Murray and Varley loop tests is that in Varley loop test provision is made for the measurement of total loop resistance instead of obtaining it from the relation R = ρ l/a.

7. In what way Varley loop test is advantageous over Murray loop test?

Ans. In Murray loop test sound cable resistance must be known whereas in Varley loop test it is not so.

8. What is the essential requirement for performing capacity tests on cables ?

Ans. The essential requirement for performing capacity tests on cables is that the core to be tested has a good insulation resistance.