*sigh* OK, I'm getting a little tired of repeating this, but being grounded should not even enter the discussion. I guess I'll go into this in a little more detail (inspired by AGX-17's poison chemistry up there!).
"Grounding" is an approximation. Metals have a very low resistance as compared to non-metals. When you have an unbroken link of low-resistance material to the "ground" (the place where all stray electricity goes) then you can approximate the potential at the top of this link to be the same as the ground, i.e. zero. This means that any electricity striking the top of this link is effectively going straight into the ground, ignoring any other alternative paths (through your adventurer's body). This protection is not going anywhere just because a piece of the metallic link to the ground is replaced by a non-metal. The approximation only becomes a lot worse. The metallic parts of your armour are still much lower in resistance than the human body, however sweaty. You will get shocked at those points in the link where the "grounding" is broken, but you will not feel a thing in those parts which are covered by metal. Contrast this to an adventurer wearing Enchanted Elven leather armour - the sweaty human body is probably always a lower resistance pathway for electricity than the armour. The more metal your armour contains, the fewer the parts of your body that get shocked. Sit in a car in a thunderstorm - the metal protects you from a significant amount of HP damage even though cars have rubber tires.
Josh's point about Accuracy bonuses is not exactly valid IMO. True, the more metal your armour contains, the more attractive it becomes to being struck by a bolt of electricity. But it also provides more protection from damage, even if it is not grounded. If the accuracy bonus translates into a DT penalty, the "protection" I'm talking about should translate into a high DR bonus. Does a DT penalty cancel out a DR bonus? I have no idea. I don't see how it leaves you with a net DT penalty though.