What Does It Mean That What Should Be 120v Outlets In My Home Measure About 158v And What Should Be 240v Measures About 317v? All My Appliances, Etc. Work Fine, But Is This Damaging On A Long Term Basis? What Can Be Done To Bring The Voltages Closer To Standard?

Today, I was issued my permit to add a sub-panel out to my detached garage. It went very smooth execpt for one issue and that pertained to the sub-panel grounding. I will be running 4 6AWG wires from the main panel in our basement to the detached garage subpanel approximately 40 feet away from the main breaker. Of course, neutral and ground will not be bonded in the subpanel. I planned on adding a grounding rod out back behind the garage in order to ground the subpanel. The inspector, on the other hand, said the grounding rod was unnecessary since I was already running 4 wires from the main panel. Is the inspector right? Do I not need a grounding rod for the detached garage sub-panel? Just an FYI, our municipality still uses the 1996 NEC, if that makes any difference. In addition, the main panel is only grounded to the cold water pipes: it does not have it's own grounding rod either. That's very typical around here.