This surge arrester, surge protective device protector one pole: Provide protection against surge current of circuit single phase 220V.
Two pole: Provide protection against surge current of L and N phase to earth of circuit single phase 220V resulted from lightning.
Three pole: Provide protection against surge current of S phase of TT, TN-S system 380V, and also protect S to earth of IT TN-C system of 380V
Four pole: Provide protection against surge current against S, N to earth of TT TN-S system of 380V.