Know the earth Circuit fault using earth lamps

• Assume that the earth lamp switch is in off position.
  
• Now the neutral of the star connected primaries of the three transformers is disconnected from the earth.
• Hence the voltage across transformer primary is the same even if there is an earth fault in the ships electrical system or not.
• Hence the three indicator lamps connected to the respective transformer secondary's burn at the same brightness.
• To test the the insulation resistance of the ships electrical system to Earth, turn on the ELS to test position.
  
• Now the neutral of the star connected primaries of the the lamp Transformers is connected to earth.
• Assume that there is an Earth fault in phase R, the lamp R would be less brighter than the other two lamps, B and Y.
  
• If it is a solid Earth fault, the lamp R good go off totally.
• If there is no earth fault, all the lamps would continue to burn with same brightness.