If you are looking for warratie the continous service of the plant, IT Earthing system is the solution, but the main problems are:
– Once your have the first failure, its dificult/expensive to find where is the fault.
– The defect current is low, but the voltage arrise is high, so the life of the components will be longer by the lower temperature stress, but the life of the component will be shorter due the isolating stress. 400V will not have problem, but 690V could be.
– Every electronical component which has a electromagnetic compatability filter (mandatory in Europe) send high frequency current to earth. If the installation has many electronic components you must set your isolating meter at a value that cannot detect a real isolating defect.