The majority of my home has an ungrounded electrical system (at least, there's no green line in the boxes). However, the addition in the back of the house IS grounded. Can I ground the original wiring simply by tying the cases to the ground line in the addition, or would I be better off calling a licensed electrician for the task. Also, if I need to call someone, roughly what would the job cost, assuming I've provided adequate info for an estimate?