the coil works thru induction. the trigger turns the coil ground on and off, so the primary windings magnetic force collapsing and turning back on, induces a charge in the secondary windings, and there are more secondary windings than primary's, that's how you get 40,000 volts, or 20,000 volts, whatever your working with BUT, the coil can draw 40 amps intermittantly, this is why you don't fuse.