$($a$)$ With reference to marine electrical distribution, explain EACH of the following terms:

$($i$)$ earth fault;

$($ii$)$ insulated neutral;

$($iii$)$ neutral earthing resistor.

$($b$)$ Sketch a labelled circuit diagram to show how a d$.$c$.$ voltage, derived from the three$-$phase supply, can be used to monitor the insulation resistance of the system.

$($c$)$ Describe the indication obtained from the arrangement sketched in Q$8($b$)$ for EACH of the following situations:

$($i$)$ no earth faults;

$($ii$)$ an earth fault on one line.