Citel ds440 230 g 3 phase 4 pole ac surge protector type 2 citel ds440 230 g p citel ds440 type 2 surge protectors are compact devices designed to protect 3 phase neutral networks at the main switchboard p p they provide common or common differential mode protection and use high energy varistors equipped with thermal disconnectors and failure indicators to comply with standards the ds440 is din rail compatible and constructed with a fixed base that houses a replaceable plug in module f