Upstream Breaker/Fuse for Surge Arrester

If my guess is correct, the surge arrester would have been connected between phase and earth and not between phases. If true, the phase-to-earth voltage in a 400V system is 230V and thus there may not be any problem with 350V arrester.

The fuse is selected to protect the cable in case of feeders and to protect the arrester in case of surge arrester. Thus the fuse rating doesn't depend on the cable short time withstand and instead on the discharge rating of the arrester.

Hope the above is helpful.

Phase to ground is ok with selected device.

Phase -to- phase will of course, require an appropriate higher rating. However, most systems use 3 Mode protection,which includes phase to phase protection as well as phase to ground, and ground to neutral.The fuse is used to prevent catastrophic failure of the surge suppressor. They are designed to absorb a very brief surge, but sometimes they will weld in the shorted condition and if not fused, they will explode and cause further damage.

The status of a surge suppressor can not be determined by looking at it.

Size your fuse to protect the wire feeding the surge suppressor.A quick acting non time delay fuse is recommended.An excluder type fuse holder is recommended to prevent replacement with a standard fuse.

I recommend a neon indicator(with proper resistors in series) across each suppressor.When light is on, suppressor is ok.

These indicators should be panel mounted so as to be readily visible externally.

If light is off,a failure has occurred and the suppressor must be replaced.These devices are good for one-time only, and are not reliable after absorbing a surge.

Hope this helps.

Dear All,

Thank you very much for your comments.