surge arrester installation

[pist0n]

I heard that when installing a varistor for surge protection in an electrical installation, a HRC fuse should be connected in series with the varistor. I coudn't understand the requirement of this series HRC fuse. Anybody know the reason ?

[Mr2Mike]

Because a varistor can only absorb relatively small amounts of energy. If you get a sustained surge or multiple short surges in succession, it will undergo "catastrophic deconstruction". The idea is that the HRC fuse ruptures before the varistor spits its guts everywhere.

[anonymous-user]

It also depends upon if your varistor (or TVS, Transorb, MOV etc) is placed in series or parrallel with the line to be protected.

[Mr2Mike]

Max_Torque said:

It also depends upon if your varistor (or TVS, Transorb, MOV etc) is placed in series or parrallel with the line to be protected.

I can't see a varistor being of any use in a series connected circuit since it's a voltage dependent device rather than current driven.