On 2009-03-20, N_Cook wrote:

I'm amazed they last as long as they do , 400 turns or so of paired primary
wires layed together touching and thermal cycling / chaffing possibility
along the lacquer . Certainly not produced in a clean-room so any amount of
microscopic grit between the wires, what is the thickness of 2 layers of
lacquer to resist pk-pk voltage of 350V , let alone mains surges?

peak to peak is half of that between series-connected windings.