Interesting possibilites. I wouldn't put 4.2A through 7/0.2. Even 16/0.2 is pushing it. It all depends on what temperature rise you can tolerate in the wire. I'd prefer 32/0.2 and that is the problem - with price and availability. I spotted CSE and their prices are good, but they charge £7.50 minimum delivery. With the conversion costing hundreds of pounds, is this a "ha'peth of tar"? Maybe I'll try the unscreened wire and see what happens. I can always re-wire.