36 Chapter 2 • Cable joints and switchgear


Exercise 2.5 1. Mention two types of disconnectors referred to in SANS 10142.


2. With reference to SANS 10142, on which side of the main circuit-breaker must the switch-disconnector be connected?


3. Briefly describe what a relay is. 4. Briefly describe what a contactor is. 5. What is the main difference between a contactor and a relay?


6. Briefly describe the differences, with regard to the operational features, of a disconnector, a relay and a contactor.


7. Briefly describe the constructional differences that exist be among a disconnector, a relay and a contactor.


8. What is the function of a disconnector? 9. What is an isolator used for? 10. Briefly explain how a relay operates. 11. Give one example of the use of a relay in practice. 12. What is the main functional difference between a relay and a contactor?


13. Consider a disconnector and a contactor. Which would be used to control a circuit and which would be used to isolate a circuit?


2.7 Miniature Circuit Breakers (MCB)


Low tension circuit-breakers of the domestic and small industrial type may be of the single-phase or three-phase type.


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