15.4 Volts between ground and neutral gasbuddy touch


Just got this email from a NSZ reader yesterday. After talking to him we found that the campground wiring measures around 15 volts between the Neutral and Ground in every power pedestal outlet. The EGC to an ground rod is a fraction of a volt, but the Neutral measures 15 volts above earth potential. While it’s normal to see a few volts difference between Ground and Neutral on a loaded circuit, I’ve never measured 15 volts unless something was disconnected. And this appears to be on EVERY pedestal in the park, so it must be happening at the Service Panel. Do you think someone forgot to bond the Neutral and Ground together in the service panel? That’s the only thing that makes sense. This is a National Park so the Army Corp of Engineers is apparently in charge of the campground wiring. I guess they make wiring mistakes too…

I am reading 15.4 volts between the ground an neutral on an rv I am servicing for a client. I have combed through your no shock zone details and have tested everything u recommend for hot skin and reverse polarity checks. Any thoughts on what might be causing the reading?

The problem is that (last I looked anyway, which was a few years ago) there is no regulation requiring USA electricians to confirm PSCC, so most folks simply haven’t got a PSCC tester. A low resistance tester, qualified to operate on mains, that passes a significant test current is the next best thing, and measure the neutral to earth resistance, which should be low. Third best thing, but a bit dodgy, is a car battery and a headlamp bulb as a continuity tester, and use that to check the continuity of the ground to neutral; the bulb should light.

The scary thing about TN-C-S installations (which is what the USA mandates) where there is no equipotential zone and one is in contact with "real" ground, ie that soil stuff, or worse still, in water in the presence of electrical stuff, so, for example, a marina) is where there is a potential difference between the ground pin on an outlet and the soil. Then there is the very real possibility of being shocked by differences in ground potentials. There is no NEC-compliant protective device available for installation purposes that can prevent ground-to-ground shocks.

Yes, we’re doing that right now. Since this is federal land, the Army Corp of Engineers is actually the AHJ and there’s a forest ranger living on the site. The ranger has been notified and asked to contact the Army Corp of Engineers to find out which local contractor actually did the electrical work. I’ve told them to contact me ASAP to answer any questions I can about the danger of the situation.

The RV Technician who contacted me has sent a pile of pictures showing voltages he’s measuring at the pedestals, and the most he sees from the Ground wire to earth is 0.7 volts. So there’s no immediate hot-skin voltage with reference to earth potential at the moment. But he’s still reading Neutral to EGC voltages of 20 volts or more. I’m considering calling the ranger and asking them to have the RV owners unplug and evacuate the campground, but since there’s no hot-skin voltage on the RVs right now that might be premature. But I do know the RV skin voltage could change in a second, so I’ve aked the technician to monitor it closely.