This can result in disconnection of a large(r) area or more damage to the switchgear in a MV/MV substation. To determine the chance that this will happen, in the first place the chance on failing of the relay itself is relevant. But, as long as there is no fault in the network that has to be switched off, there is no large(r) outage or damage. Therefore additionally it is necessary to determine the chance that during the time that the relay is defect, a fault in the network will occur. When the failure of the relay is detected in time, for example during periodic maintenance, and the relay is then repaired or replaced, there will be no problem. The chance that a latent relay defect will result in an actual failure is called ‘manifesting chance’.