Originally Posted by darkphader
I'm in an older house and the outlets have no real ground. Some of them have a NEMA 5-15R receptacle but a tester shows an open ground. Is this of real concern to my AV and/or computer gear...
It is a safety and code issue. If there is no ground, you need to install either 2-prong receptacles or GFCI receptacles with the label "no ground present". The ground is intended to provide a low impedance path so that the breaker in the panel will trip on a fault condition.
...how can I verify there is an effective path to earth ground?
You can hire an electrician to test the grounding electrode resistance with a megger. Electrical code almost everywhere in USA requires max of 25 ohms. Over that and a second electrode is required.
FWIW surges do not magically disappear into ground. You want a low impedance ground to allow surges such as lightning to return by their normal path, which is the ground. Other surges will return via the electrical service.
Does the open ground on my receptacles nullify the effectiveness of the whole house surge protector?
What you see at the receptacle is irrelevant to the function of a whole-house device. The quality of the ground at the service entrance is what is important.
Does the open ground nullify the effectiveness of both MOV type and series mode surge protectors at point of use?
Won't affect a single mode surge protective device, either MOV or series mode. With a 3-mode MOV-based device, you will lose 2 of the modes. You will still have L-N protection, which is what the inventor of series mode protection recommends.Edited by Colm - 3/8/13 at 4:16pm