Installation of SPDs in TN-, TT-, and IT-Systems according to HD 60364-5-534

The installation of SPDs in a specific power distribution system must be coordinated with the protective measures against indirect contact (fault protection) and with the corresponding protective devices and their capability to withstand impulse currents.
This coordination depends on the type and earthing arrangement of the power system, as there are TN-, TT- and IT-systems according to HD 60364-1 and the corresponding protective devices may be:
• overcurrent protective devices;
• residual current protective devices;
• insulation monitoring devices.

spds installation in tn, tt and it systems



1: OCPD 1 OverCurrent Protective Device at the origin of the installation (e.g. in the main distribution board)
2: Main Distribution Board (MDB)
3: Main Earthing Terminal
4: Surge Protective Device(s) (SPDs)
4a: Surge Protective Device connected N to PE (N-PE SPD) when connection type CT2 (3+1 connection) is applied
5a/5b: Alternative connections to PE (preferably the shortest route, or even both connections as required in some countries)
6: Equipment to be protected
7: Residual Current Device (RCD) (in most cases this will be a RCCB or a RCBO)
7a: Selective Residual Current Device (e.g. type S RCD)
F: OCPD 2 OverCurrent Protective Device required by the SPD manufacturer
Ra: Earthing resistance of the (consumers) installation
Rb: Earthing resistance of the power supply system

spds installation in systems 

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