Finding an Earth Fault on a 220V circuit is comparatively difficult than a 440V circuit. The main reason being the lighting circuits found all round the vessel. However, any earth fault alarm with respect to a 220V circuit is usually treated as important but not an emergency.
- Check the trueness of the alarm.
- Isolate the complete Group start panel for a lighting division one by one.
- Check the Earth Fault indicator for status (still faulty or normal).
- If faulty, then put on the breaker which is put off earlier and isolate other group start panel for lighting circuit.
- Once the group start panel is identified, then individual lighting switches are turned off one by one and checked for the alarm condition.
- When any switch when turned off and thus the condition becomes normal, then this lighting circuit is marked and then inspection is done on the particular light for abnormalities.
Ingress of moisture is most common reason for an earth fault.
Alternate Idea: Instead of turning off breakers one by one for the lighting circuit, I followed a method where I turned off all lighting circuit of a particular doubted area. This method helps usually when there are two or more earth faults in 220V lighting circuit. By turning off all the breakers of a particular area, then switching on the breaker one by one will eliminate multiple earth faults.
When I turned off lighting switches one by one, it was difficult for me to identify multiple earth faults.
Once the particular faulty circuit is spotted, then we have to further break them into individual dividable pieces and check them for earth faults. For this as usual, we use megger against earth.
By removing fuse of the two phase lines, each line can be tested and the fault pinned down.