There are three key elements to select:

1.  Maximum continuous operating voltage Uc

No effect on the existing system when there is no surge.

Maximum continuous operating voltage Uc ≥ System’s maximum continuous operating voltage that may occur.

When surge occurs, power SPD can quickly discharge surge, play sprotective role.

Discharge capacity (In/Imax etc) should meet the requirements of the system design; The voltage protection level Up should match the voltage-resistant Uw of the protected system. Up＜0.8*Uw

2.    Discharging capacity

Select nominal discharge current (In) or impulse current (Iimp).

In is the maximum surge current that SPD will not damage when passing the standardexperiment waveform current and the specified number of experiments.

Iimp is the current defined by the three parameters of peak current, charge and W /R

Normally for power distribution system，we use 3 stages SPD for protection, one SPD for one stage. For example, the main cabinet, which is normally at the boundary of LPZ0 and LPZ1, Iimp=15kA is recommended.

The distribution cabinet, which is normally at the boundary of LPZ1 and LPZ2, In=20kA is recommended.

3.    Combination

Make sure what power supply system is. For example,

Remark: what's the meaning like "TN-C" ?

First letter represents the grounding status of the power:

T：Grounded

I：not grounded or grounded by high resistance.

Second letter represents the grounding status of exposed conductive part of the equipment's.

N: Grounded through power’s.

T: Grounded directly nearby, without connecting to power’s

C-combination，N and PE are combined.

S-separation，N and PE are separated.