Q11. (a) Explain, with the aid of a sketch, the principle of operation of an earth leakage detection system of the instrument type (6)
(b) Explain why an insulated neutral system is used extensively on-board ships (2)
(c) State, with reasons, why a single earth fault on an insulated neutral system should always be cleared as soon as possible (2)
Simple & easy question to score marks. Draw a neat sketch for ‘a’.
>> Question ‘a’ - This was where a number of candidates went badly wrong. The question asked for an instrument type earth leakage detection system and they produced earth lamps. That's six marks lost straight away. If you look in Practical Marine Electrical Knowledge page 2/8, just after the bit about earth lamps, Mr Hall sketches and describes what he calls 'instrument type' earth leakage detection systems. It's a fairly simple system and I would have thought it would be in the student notes issued by the colleges. This question will be used again, and hopefully this message will have got through by then.
In summary, the candidates who did not answer question 9 fared worse because a lot of marks were lost in 10 and 11.
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