Voltmeters run you a few dollars at your local hardware store. It's advised that you check out your current and grounding every so often to make sure everything is running smoothly. Better to be safe than sorry.
And it also exemplifies the whole "unplug when not in use" idea. 1 it saves you electricity, 2 its for safety reasons.
Even more important, the overheated charger and cord didn't start a fire and burn your house down.
scifan57, iPhone Forums Moderator