surge protection device (SPD) can be connected to between the L (phase), N (neutral), PE (protection line), such as L-L, L-N, L-PE, N-PE, these connections is called protection mode, which has relation of power supply system grounding type.
According to IEC61643-11:2005, the grounding type of power supply system can be divided into: TN-S system (three-phase five-wire), TN-C system (three-phase four-wire) TN-CS system (replaced by a three-phase four-wire three-phase five-wire), IT System (three-phase three-wire) and the TT system (three-phase four-wire, power supply and ground has little direct connection, the load side of the electrical equipment exposed to conductive part of the grounding and power connections without electrical grounding contact.)
Currently, the protection-mode of surge protectors has 4 protection modes (L-PE, N-PE), which are three Fire Wire connect to the protection line, neutral line connect to protection line.
Some of the protection mode is full mode protection (L-L, L-N, L-PE, N-PE), which is connected between three Fire Wire, three Fire Wire Line connected to neutral line respectively, neutral line connected to protection line. All models up to 10 models, in common 3-phase star-grounded is 10 models.
The protection mode commonly used in China is 4 modes of protection (the reference to IEC standard). 4 mode surge protection device does not protect all possible circuit which current will go through, such as between Fire Wire to FireWire between the (L1-L2, L1-L3, L2-L3), FireWire to neutral line (L1-N, L2-N, L3-N).