Why is earth grounding important ?

[tortuga]

And this actually makes the case for how little the resistance of the grounding electrode system really matters. Many places of the country have lots of ungrounded Delta distribution. Most rural areas in upstate New York where I live are this way.

Interesting its here also but considered 'legacy' do they keep the ungrounded delta on upgrades?

So a building served from these won't have the massive MGN grounded in a zillion places. Instead they will just have an earth connection at the pole, with a good chance that has been cut off and stolen by thieves. That leaves the electrodes at the building as the only Earth connection. My point is I have never noticed an increase in surges, damaged equipment, less reliable operation, or anything negative whatsoever on these systems compared to one served by an MGM with its super low resistance ground.

I wonder if thats because of that big court case on Electrical Trespass or "Stray Voltage" from a what I think was a MGN system in NY. However I might have that backwards it may have been a delta system.
Some homeowners had high levels of stray voltage around a substation after it was 'upgraded' back around 2012 they sued.
I think they (the plaintiffs) proved the Utility (NYSEG) was aware the (MGN?) system caused stray voltage.
The utility tried to fix it by installing the fancy 'Ronk voltage blockers' etc.
Basically a utility is liable for 'Inverse Condemnation' when their (neutral) current leaks across a property causing a 'loss' as then you cant enjoy your new pool or your dog gets shocked etc. Even if a utility has an easement for electrical wires, they need a different easement for using the earth as a conductor. There have been recent successful suits that utility easements for electrical wires dont cover 'fiber optic', due to the exact wording of utility easements, though some may allow SWER or MGN explicitly.
I cant remember the outcome of the case but I remember it was in NY and it cost the utility millions just in legal fees, was big enough that other utilities started reconsidering upgrading to that system as 'risky'.
There have been other cases around dairy cows and pools.

 

[electrofelon]

Utilities learned early on to ground their distribution lines otherwise huge arcs would erupt from their generators at the central station. There are reports of generator mechanics getting hit by large arcs just standing nearby. Apparently the voltage gradient over miles of transmission line is huge.

I bet that grounding at the service was required by the utility just due to them being paranoid about previous insufficient grounding.

 

[electrofelon]

Utilities learned early on to ground their distribution lines otherwise huge arcs would erupt from their generators at the central station. There are reports of generator mechanics getting hit by large arcs just standing nearby. Apparently the voltage gradient over miles of transmission line is huge.

I bet that grounding at the service was required by the utility just due to them being paranoid about previous insufficient grounding.

Hmmm, that sounds like BS. For one thing there are transformers between the generators and the transmission lines, and then again between the transmission lines and distribution lines. So I don't see how the grounding topology in one "section" would effect the other. I guess I would want some more specifics on exactly which conductors are/were getting these voltage gradients and arcs. Like I said, lots of ungrounded Delta distributions still out there, geographically most of New York State. never heard of problems.

 

[electrofelon]

Interesting its here also but considered 'legacy' do they keep the ungrounded delta on upgrades?
.

The common scheme they use for upgrading, is to just upgrade the first 1/4 to 1/3 of the line (total guess, just making a point) to 13.2/7.62 KV WYE, and at the end of that hit a transformer platform that refeeds the older 4800 Delta lines. Once you start looking, you see these transformer platforms everywhere.

 

[CoolWill]

Hmmm, that sounds like BS. For one thing there are transformers between the generators and the transmission lines, and then again between the transmission lines and distribution lines. So I don't see how the grounding topology in one "section" would effect the other. I guess I would want some more specifics on exactly which conductors are/were getting these voltage gradients and arcs. Like I said, lots of ungrounded Delta distributions still out there, geographically most of New York State. never heard of problems.

Maybe, but it is the explanation given by my 1917 Hawkins Electrical Guide.

 

[electrofelon]

Maybe, but it is the explanation given by my 1917 Hawkins Electrical Guide.

I would be curious for more details. maybe they were cranking up the voltage beyond the design to overcome voltage drop? Or in a uni grounded system the potential of the grounded conductor could get pretty high. It's about all I can come up with without more specifics.

 

[kwired]

voltage to dump directly to the earth, where the lightning wanted to go anyway.

lol

a big NEGATIVE opposite effect at my son's house a few years ago, having a good ground (ufer) on the house CAUSED a lot of damage
direct lightning strike to 150 ft DFir tree 10 ft from house, big lightning gash in tree down to the roof level of the house, then lightning jumped to the grounded floodlight at the eave - blew the computers and the inverter in the heat pump, NO gash in the tree bark from huse eave level to ground, lightning jumped TO the house vs. continuing down the tree to ground!

An UNGROUNDED house would have had less equipment damage.

I have seen somewhat opposite issue with lightning before. Is a little hard to predict what will be the less resistance path or what gap may be jumped in a lightning event.

Got called to a kitchen fire many years ago that started after a lightning event. Supposedly lightning struck a pole nearby, and entered house via the electric service. This house had no grounding electrode connected to electric service. The fire started behind the range, we figured there was likely an arc between a range receptacle and a gas pipe behind the range that started the fire. Would've an electrode at the service prevented that fire? Maybe, still hard to tell for certain.

 

[kwired]

One of the "reasons" for grounding systems is supposedly static. Anyone experience real life situations where static build-up is an issue? I'm thinking that would most likely occur in arid and windy locations. Anecdotally, I heard that this was one of the issues the Army faced in the desert which directly resulted in the "invention" of the CEE by Mr. Ufer himself. Something about ammunition storage. Yeah, I could see why you might not want static discharges in ammunition storage buildings.

Satellite dish installers are fairly adamant about a grounding connection to the shield of their cables, though most of them obviously don't look at it same way electricians do when it comes to how/where they connect it. Electricians want it bonded to electric system, some simply because that is what code says but don't necessarily know why. The dish installer is doing it in his mind to minimize static buildup caused by the wind blowing past the dish.

 

[CFI]

^{I am a origin and cause fire investigator and licensed electrical contractor. Best way I can tell you is I recently investigated a house fire where the utility neutral came in contact with a primary (7200 volt). The house was heavily damaged by fire and the neutral failed from the high voltage where it came out of meter base and extended to interior main panel. I suspect weather/ uv from sunlight added to the failure. However the line fuse nor transformer opened immediately like it should have, although the house has a driven ground. If the driven ground was designed to open a fuse, it did not. The earth resistance is just too high for this to occur. The transformer is approximately 75 feet from the house and by the way, there was a driven ground in the utility pole.}

 

[petersonra]

IMHO the connection to earth is part of bonding vs high impedance 'faults', for example the tiny leakage current across the transformer from the HV distribution, 'static' charging from wind blowing across wires, etc.

If you don't _bond_ two different conductive items together, you have the possibility of a significant voltage between these two items. The connection to earth ground is IMHO simply bonding to ensure that the electrical system is not an unintended capacitor relative to the earth. Without _some_ bonding, then on a cold dry day a residential electrical system could easily float to several thousand volts relative to ground. This 'static' high voltage would cause small discharges that would damage insulation or shock people.

so why has this never happened on industrial delta systems with no ground reference.

 

[LarryFine]

Welcome to the forum.

^{If the driven ground was designed to open a fuse, it did not.}

It is not. The neutral conductor is that pathway. If it's compromised, the next-best pathway is a solid connection to an all-metal water-service system to the neighbors' neutrals.

Add to that the insulation damage caused by the primary voltage, and you have arcing to the non-grounded conductors. The entire house was effectively energized for a while.

^{The earth resistance is just too high for this to occur.}

You have answered your own question.

 

[winnie]

so why has this never happened on industrial delta systems with no ground reference.

One of the known failure modes on ungrounded delta systems is a small 'restriking' fault in a motor 'pumping' the entire system voltage to ground up to higher than the normal L-L voltage. This causes other devices on the same system to suffer insulation failures.

https://www.eaton.com/content/dam/eaton/markets/healthcare/knowledge-center/white-paper/transient-overvoltages-on-ungrounded-systems-from-intermittent-ground-faults.pdf

The tiny damage from what we ordinarily think of as static electricity is probably not noticed in industrial systems.

Back in the late 1800's and early 1900's when there were arguments about grounding, insulation systems were poorer, and there was probably more leakage across transformers, so high impedance sources of high voltage were probably a bigger issue.