However, I'm not sure about the intent of the blank. It seems really unlikely that it would be meant to fire during normal operation, doesn't it? Destroy the arrester on the first surge? Hmmm... maybe it was intended to destroy the arrester only after long-duration operation, such as when the arrester failed to open following a surge? I'm even a bit unsure what "destroy" means in this case, since the position of the blank is so odd. It's separated from the "guts" by a large metal plate (see top picture), and the guts are spring-loaded, too, so it seems like they'd be protected pretty well. I'm left to wonder if the terminal containing the blank was meant to be completely blown off (seems really unlikely), or if the blank's firing was simply intended to "poison" the atmosphere within the arrester, making it non-conductive ...? Maybe the blank contains some special "stuff" Well, it is an interesting little mystery, isn't it?

Finally, just because it's kind of neat, here's a picture of the SiC cyllinder (the actual varistor element):

So... if anybody wants one of these, just make sure it's not illegal for me to ship you live ammunition!