Hi Houses4Rent a lot of people, I would go so far as to say that the majority of people [I]electricians [I]included do not understand the purpose of a earth leakage unit and consider it unecessary and causes nuisance tripping. Unknown to them the tripping function is there as a protective device and by functioning properly is indicating that there is a fault on the circuits or part of the circuits that are being supplied by the E.L.U. So basically an E.L.U. is a essential safety device designed to protect life and property. Lighting circuits in some installations are not covered by E.L.U. as a safety precaution (make sense, you must have illumination)