The ETITEC D series unit is a surge arrester primarily used for interior purposes. The ETITEC D series Group D surge safety is as per the norms of VDE category D and this safety compliments to IEC class III.
The ETITEC D series unit must be set up instantly prior to the protected load. This is to protect it from indirect thunder hits. If at all there is a constant arrester loss, thermal safety of the unit is triggered, that indicates the damaged arrester. In such cases where arrester has been damaged, you'll need to to change the varistor overvoltage insert. The basic cover stays on the top hat fitting DIN rail.