You do not need a few LAYERS of heatshrink. That's BS. The only case where you need more than one layer is in high voltage application (1kV or more), and even then, you're doing it wrong if you're relying on heatshrink to insulate your wires/connectors, there are better things like epoxy and ceramic.
One layer is enough. Anything to keep them apart.
On the welding thing: My ooold hobby when I was younger was to make sparks. That's about it. I went from high voltage (200kV+@1mA+), to LVHC(1kV@20kJ) dead short, to HVHC(RF 500kV@20mA+). xD Then there was the LVHC transformers, where you have 50kW worth of 40VAC energy shorted, dissipating a crap ton into whatever you shorted it. Whoo for 4/0AWG wire secondaries when winding transformers around 200lb laminated iron cores from old distribution transformers!!! //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif