I think this question should have some serious discussion with the manufacturers, because it points to a potential difficulty with SPDs fitted on larger systems. Whilst I think that failure dead short of a device is very unlikely, it seems to be a serious snag and cost to have to fit a series fuse to limit potential fault levels. A simple design feature such as a fusible connection, would fail open at extreme fault level and even if an arc is formed would reduce current to manageable levels. In fact I would be more worried that short circuit failure would result in perhaps a few 10s of milliohms and the resulting dissipation start a serious fire, but with little possibility of an upstream CPD operating. In many ways I am far from convinced that SPDs at the supply end of an installation are necessary, and the idea that this may prevent damage to appliances, such as VFDs will work. Semiconductor designs already contain features to limit surge damage, and are in general very reliable unless there is a direct lightning strike, and in that case an SPD is unlikely to make much difference anyway.

I think this question should have some serious discussion with the manufacturers, because it points to a potential difficulty with SPDs fitted on larger systems. Whilst I think that failure dead short of a device is very unlikely, it seems to be a serious snag and cost to have to fit a series fuse to limit potential fault levels. A simple design feature such as a fusible connection, would fail open at extreme fault level and even if an arc is formed would reduce current to manageable levels. In fact I would be more worried that short circuit failure would result in perhaps a few 10s of milliohms and the resulting dissipation start a serious fire, but with little possibility of an upstream CPD operating. In many ways I am far from convinced that SPDs at the supply end of an installation are necessary, and the idea that this may prevent damage to appliances, such as VFDs will work. Semiconductor designs already contain features to limit surge damage, and are in general very reliable unless there is a direct lightning strike, and in that case an SPD is unlikely to make much difference anyway.