As Dead Monky wrote - tasers can really hurt someone. I'm not really what you'd call 'a scientific mind', but as far as i remeber, tasers, and other shock weapons use high voltage impulses. And you can survive these, as they shouldn't cause any significant damage. But a Lightning Bolt/Ball spell uses something akin to their real counterpart. As with wall sockets, it's not the voltage that kills - it's the sole amount of electrical current, that hurts the target. So it's not a 'safe' (or should i write 'semi-safe') ammount of electricity. Even if a Force 3 Lighning Bolt isn't much, it's still as painfull as a .22 round. Even if your armor absorbs most of it...
And as for what Voydangel wrote, yes, but 'immunity to normal weapons' means knives, clubs, bullets, and shotgun shots. Not shoving a live wire into the spirit's manifested form... But i'd still say: magical, or no, you can't hurt a fire spirit with fire. That's just stupid...