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Class 2 (2nd Engineer) MET 📅 Feb 2026

Exam Question

(a) Describe the circuit breaker for an a.c. generator using a sketch to show how arcing is Controlled. (b) Explain the sequence of events that might occur if the breaker opens on a short circuit and state the check you would require following such event (c) Give a safe procedure to follow should a main circuit breaker fail to open under fault Condition.

Reference Answer

### (a) Description of an AC Generator Circuit Breaker and Arc Control
An Air Circuit Breaker (ACB) is the primary protection and switching device for a marine AC generator. It is designed to make and break the circuit under normal load conditions and to automatically interrupt the circuit under fault conditions like overload and short circuit.
**1. Main Components:**
* **Main Contacts:** These are silver-plated copper contacts designed for low resistance and continuous current carrying. They are the first to make and the last to break.

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