ECN Forum Forums General Topics of the Trade General Discussion Area Is this safe?

I'm about a month away from changing the service in my own home. I'm going to insert a section of plastic waterline next to the meter to isolate it.

I'm in Canada and our dirt is frozen for several months out of each year. To me, that means our ground plates will be in ice instead of dirt which probably means a really high resistance. Because our ground, or in the winter, crappy-ground, is in parallel with the poco earth return, we might get a tingle voltage between ground and cement basement floor. I won't be able to measure that because all my neighbors are using the water line as ground. My understanding is that our poco target resistance for their grounding is 5 ohms. Does anyone have any experience with this? (without a Ufer ground, of course)

When I moved into this house it was far more than just tingle voltage between the EGCs and the floor. The first thing I did on day one was connected the cooktop to a cold water pipe and that fixed the problem temporarily. Later I figured out the "ground" I was using was actually the cast iron drain pipe from the stainless kitchen sink, connected continuously by metal to the earth under the slab. (Chrome over brass tailpiece and trap, copper drain pipe)
Shortly after that I drove new rods and connected new copper from the panel to them. As time went on my GES was improved. Now I think I may be the ground for the neighbors too. I have a couple of amps on the PoCo neutral with my main breaker off. There is so much stray current going around it is hard to figure out what is going on. All of the grounding leads coming down the poles carry current, all the way up my street. The worst is almost 3 amps.



I suspect that will be true anywhere that has wye distribution tho. (a whole street, ~20 transformers, fed from a single phase) All of that unbalanced current is going wherever there is a path and a 2ga neutral on the poles is not carrying all of it. I really do not think there has been nearly enough analysis of where stray current comes from and where it goes. It has been blamed for pin holing pipes here and a number of other less noticeable issues.

Greg, if you have current on the ground with the main off, you might be the return path for your neighbors or you might be the earth return for the transformers. Do you have a pool with a lot of grounding?

Yes I think that is exactly what is happening. As I said I may be the ground electrode for the neighborhood. I am the only one within a quarter mile with an in ground concrete pool and that has to be the best Ufer ground around. The poles depend on a single strand of #6 copper, stapled to the bottom of the pole and most people just have a rod or two. When I was building my pool and deck, everything was bonded and it gets tied back to the service ground via a bunch of copper EGCs. I also accidentally exposed the rebar in my garage footer doing something else and I tied that in too. Every time something becomes "available" it gets used. I now have rods at the satellite dish and also at the HVAC condenser at the far end of the house, tied into the system.
The up side of all of this is in spite of a thunderstorm about 150 days a year, I have not lost a thing.

As soon as you have a neutral/ground connection anywhere and bonded water pipes the pipes can and will become a return path. The whole stray current issue is the main reason why some distribution network operators in Europe prefer TT systems where the building grounding conductors are only connected to rods/UFER but not to the neutral. The neutral is only earthed at the transformer. The downside of TT is obviously the considerably higher impedance, requiring additional earth leakage protection (i.e. an RCD for all circuits).

Re: impedance of rods: that totally depends on local conditions but 5 Ohms is pretty low. Very low for rods in fact. When ours was newly installed it measured at slightly over 8 Ohms and I'd say we've got decent conditions here (mostly clay). By OVE standards, up to 100 Ohms are considered acceptable.

That was the thinking when the NEC stopped regrounding the neutral beyond the service disconnect. They were trying to avoid neutral current in grounding conductors. They started with "no parallel paths, then they just stopped allowing 3 wire feeders to additional buildings altogether.

When I went to school, they taught that, if a neutral and ground were both taken to a barn, they must be tied together and ground rods installed. The instructor said it is known that there is a parallel path but it is better than what can happen if they aren't tied together.

This is what can happen if they are not tied together:

You can lose the ground connection and never know because everything still works. Then, if there is a fault from hot to ground, the breaker might not trip.

With a water bowl frame tied to hot and the cattle standing in their wet poop, they will be electrocuted.

If the animals don't get it, a farmer or electrician might turn the power off to a piece of equipment but when they open it up, there is voltage between neutral and ground.

Why are we going back to a proven failure?

I assume you mean the "grounding" connection (the egc going back to the service disconnect in a 4 wire feeder) but if you have a 3 wire feeder that becomes a lot worse than in a 4 wire feeder because it is an open neutral condition along with all of the issues of a lost EGC added on. I suppose the lesson is make sure you don't have a fault in the neutral or the grounding conductor. It is not going to end well.

An open neutral is repaired immediately because the equipment quits working. An open ground remains until someone gets a shock, or something dies. The old way, that we are returning to, wasn't better.

Wouldn't a better solution be to take an insulated neutral and and ground, both of the same size and connect them together at the out-building? Then, we would have half the chance of any fault and it would never be an open ground that couldn't be detected.

Ground fault protection isn't a good solution because some equipment won't work with GFI protection. VFDs for example.

While you are providing redundancy when you reground the neutral, you are also putting neutral current on the grounding conductor. I could argue either way but 250.6 and 310.4 gets in the way of the redundancy argument.