Isolating Capacitors

[David Dunlop]

These little wonders just popped up a few days ago in Kevin's No. 11 Set thread I believe and they seem to have generated a lot of comments.

These items show up on a very regular basis it seems on eBay, nearly always ID'd as being a No. 19-Set item, sometimes the 22-Set, or less common, the 18-Set, and quite often flogged with horizontal aerials. Never seen them listed in any 19-Set manuals (standard sets at least), so other than the 19-Set HP, what other sets were they issued for as part of the kit?

Were these caps a standard size/shape and rating?

The intent for protection from overhead hydro lines strikes me as a bit odd. I have seen a number of photos of empty hydro poles and wall bracket insulators scattered all over Europe during the war, but cannot think of any photos I have seen with intact, operating lines. So now I am wondering if these isolating capacitors were a British interwar design, developed primarily to protect the wireless equipment in vehicles as they raced around the peacetime English countryside?

David