Depends on just how magic is powered in this setting. I imagine that this is a setting where magic interacts with ambient mana in the atmosphere rather than solely being generated by the mage, in which case, I imagine the fence works by drawing and converting mana into electricity; that or it just converts the ambient mana in a certain radius (like a couple inches) into electricity. Either way, it wouldn't really require any form of obvious power source.@BuffSoul Is it powered by some Mana stones or something.