Class II protectors operating on rcd The V-Check D range of surge protective devices has been designed for combined protection both against transient and permanent (a.k.a. TOV) overvoltages in single-phase or three-phase TT electrical power networks. 2D ONE-FASE PROTECTOR The V-CHECK 2D series of surge protective devices has been desgined for combined protection both against transient and permanent (a.k.a. TOV) overvoltages in single-phase electrical power networks. This series actuates the RCD of the installation. 4D THREE-FASE PROTECTOR The V-CHECK 4D series of surge protective devices has been designed for combined protection both against transient and permanent (a.k.a. TOV) overvoltages in three-phase electrical power networks. This series actuates the RCD of the installation.