Additional protection for devices belonging to overvoltage category II
If devices belonging to overvoltage category II need to be installed in the main distribution, you must ensure a voltage protection level of less than 2.5 kV.
If it is not possible to bring the voltage protection level in the control cabinet below 2.5 kV with the first SPD, you must install an additional SPD. This will protect devices with low rated surge voltage.
The same also applies to devices outside of the main distribution. These usually belong to overvoltage category II and therefore have a rated surge voltage of 2.5 kV in the 230/400 V network. If you cannot bring the voltage protection level below 2.5 kV with the first SPD, you must install an additional SPD, so as to protect devices with low rated surge voltage. This can be done in a subsequent distribution, e.g., a subdistribution. In general, it is much easier to connect the SPD with short cables there.