Medvekoma

Hmm, good question, though you'd still get burned very well. 

People never understand one thing: THIS IS NOT NORMAL LIGHTNING, ITS MAGICAL CASTED STUFF!!! 

I'd find it seriously uncool to just got in RP "XY's chainmail is struck by the lightning, Faraday's law helping him to ground it without any trouble.", but in terms of physics, it kind-of breaks the whole "lightning magic is powerful against armour" cliché. Having a decent coif, gloves and pair of boots along with a shirt could essentially protect you against any voltage. High-voltage cables are repaired in chainmail. And if grounded, the metal wouldn't even heat up.

Just a thought. Yes, magical lightning! I'll defo suggest a trivia to lightning magic: FARADAY'S LAW NAY APPLIES 'ERE.

You still get burned. This method will just be an annoying meta for everyone to avoid getting killed by lightning and avoid using electrical wards. I don't want a magic with a great strength become it's weakest when it's weakest trait is the slow casting.