We never had knob and tube here in the UK, but have similar issues with old properties that retain the vulcanised rubber insulated, lead sheathed cables.They were never designed with today's demand in mind and get "butchered" joints added too. Plus, you need some skill to ensure the earth (ground) continuity of the metallic sheath. Thankfully there are not too many of these installs left, but they are still there.
