Knowing status of an earthing switch in MV switchgear, contact visibility or positive mechanical indication?

Safety of personnel operating or maintaining MV switchgear is crucial. When work needs to be done on an electrical installation, the equipment must be earthed, since earthing is what ensures the equipotentiality of the working area. Knowing the status of the earthing switch is then critical. The paper critically reviews the different ways to get the information on the status, coming to the conclusion that the positive mechanical indication is the most reliable.