Question for Lewy and Old Lineman.

[wtdoor67]

The following happened in a town I once lived in.

The local power co. had a small piece (about a mile) of 69 Kv. they had built on 138 framing. The only thing not 138 was the insulation. This line was operated several years at 69 Kv. with the future intent of converting it to 138 Kv. by increasing the insulation. Eventually this was undertaken.

A contractor sent about two 3 man crews to add the necessary insulators. This was typical H fixtures. The line was cleared and bracket grounded. A pin vibrated from the switch handle on one end and the switch closed. At the moment it happened no personnel were up any fixture and they were actually walking between structures. No one was injured, although they were shaken by the incident as they felt the step potential as they walked along. The line was H fixtures, with a static bar and a ground on each pole.

My question is do either of you think EPZ grounding would have prevented these folks from feeling the step potential?

My second question is for anyone on this board. I think Bellamy already posed this question but I will also. Has anyone ever known of an injury, fatal or otherwise that was caused by accidental energization of a grounded line while personnel were working on it?

As an aside. In the accident I described the foreman did the switching on one end and when he went back to the office he remarked to the superintendent that someone should do something about the switch that later closed. He basically told the superintendent that some maintenance should be done to the switch as he felt it was a dangerous situation. After the incident the foreman was busted back to lineman.

[BigClive]

What sort of switching device was it? Can you honestly see a switch closing because a pin shook loose?

Maybe the foreman saw or felt that the switch didn't seem to operate correctly when he operated it. In that instance he should have done something about it there and then, and maybe his raising the issue effectively implied that he knew there was a problem.

In that instance, given the guys were walking between the structures the only way they could have applied EPZ would have been if it was laid the full length of the ground between the towers, which would not have been practical. Did they actually feel step potential as in leg-discomfort, or just the thump through the ground?

[500 KVA]

All switches acted upon by gravity should OPEN when gravity has a chance to change its status, never close it.

Yes there have been many instances where men are killed from induction from transmission under the protection of grounds. The bracket style of grounding, not EPZ. The latest incident I heard about was in New York State back in the late 90's.

The EPZ method was developed in Washington State back in the late 50's because of men killed while under the protection of bracket grounds.

If you bring the grounds down to a ground rod, or down a pole ground, then there will be a step and touch potential issue for the ground personnel. I think the policy at my company is that on distribution ground personnel must stay clear 10 feet from any ground, and on transmission voltage it is 25 feet.

Grounds are not for your protection. They are designed to protect the equipment from damage by tripping the faulted line as quickly as possible. Bracket grounds will not save your life, but actually give you a false feeling of safety.

EPZ can save your life, but ground personnel are at risk. I guess nothing is fool proof. Just use your knowledge and experience and your best judgement. Study all the data you can get your hands on, and keep asking questions. Some day someone will have the correct answer.

1+1 will always equal 2, but maybe the question 1+1 is the wrong question to be asking.

[lewy]

The following happened in a town I once lived in.

The local power co. had a small piece (about a mile) of 69 Kv. they had built on 138 framing. The only thing not 138 was the insulation. This line was operated several years at 69 Kv. with the future intent of converting it to 138 Kv. by increasing the insulation. Eventually this was undertaken.

A contractor sent about two 3 man crews to add the necessary insulators. This was typical H fixtures. The line was cleared and bracket grounded. A pin vibrated from the switch handle on one end and the switch closed. At the moment it happened no personnel were up any fixture and they were actually walking between structures. No one was injured, although they were shaken by the incident as they felt the step potential as they walked along. The line was H fixtures, with a static bar and a ground on each pole.

My question is do either of you think EPZ grounding would have prevented these folks from feeling the step potential?

My second question is for anyone on this board. I think Bellamy already posed this question but I will also. Has anyone ever known of an injury, fatal or otherwise that was caused by accidental energization of a grounded line while personnel were working on it?

As an aside. In the accident I described the foreman did the switching on one end and when he went back to the office he remarked to the superintendent that someone should do something about the switch that later closed. He basically told the superintendent that some maintenance should be done to the switch as he felt it was a dangerous situation. After the incident the foreman was busted back to lineman.I do not think that EPG would have changed what these men felt on the ground.
I have no experience with tower work & I have no idea how good the grounding was where this instance happenned, but the better the grounding obviously the better the fault wil clear.
Most of the places where I work we have the system neutral to ground to in an urban enviroment
Something I have always thought about is having the circuits that are alive at an open point under hold off protection (they are free) so you would only have to test your grounds once, but noboddy that I am aware of does this
Also I am not aware of anybody who has been working on a line that has become accidently energized

[wtdoor67]

This happened in 73 or 74, don't remember which. GOAB is just an acronym for group operated air break switch. These switches have a section of steel linkages running up the pole to the operating rod of the switch, which is just a horizonal rod that operates left or right to open or close the switches. Most people are familiar with them. They commonly have pins with cotter keys in them to hold sections of the vertical rods together. They are locked with a padlock when in either the open or closed position.

My recollection of the incident was the men on the ground felt the step potential. Been a while.

I attended many safety meetings in 36 years and never did I hear of an injury or death ocurring in such a similar incident.

Either these incidents are not well reported or investigated or maybe it is an urban myth.

It seems to me such an incident would raise the hair on any entity and there would be a bunch of reports and many investigations around such an incident. Why is that?

[topgroove]

500kva said it best. "grounds are not for your protection". its easy to protect the guy in the air from accidental energization of a circuit. through the use of epz grounds but the guy on the ground will always have a problem. all the grounds in the world won't help that guy on the ground for those few cycles untill the breaker trips unless he's standing on a grounding matt. I've had 34.5 thrown in on me while we had a mark-uo and clearence on the line. we had bracket grounds installed in both directions and had just finished our work when there was a breakdown in comunication and the travelling opperator cleared the mark-up. when he threw in the breaker it locked out immediately and regional controll called over the radio to make sure we were OK.. We were just about to remove our first set of grounds when it happened.

[wtdoor67]

This was before the advent of EPZ grounding and I'm just sure those men just placed grounds on either side of their work site.

I'm aware that grounds won't really protect, and I have always thought people had a false sense of security from them.

However I am still curious about anyone knowing of a similar incident that injured anyone. Like I said I have never encountered in a safety meeting of something of that nature hurting someone.

I have heard of many incidents but I try not to mention anything that I have not seen documentation such as you see in a safety meeting.

Still curious.

No one seems to respond to the assertion of Dolan labs that led to AEP disavowing the pertinence of EPZ grounding? AEP is a large corporation and are they not sharing their findings with other entities?

[bigjohn5638]

dielectric overshoes or eh rated line boots will protect from step potential under normal conditions,not standing indeep mud or water.

[wudwlkr]

No one seems to respond to the assertion of Dolan labs that led to AEP disavowing the pertinence of EPZ grounding? AEP is a large corporation and are they not sharing their findings with other entities?

No one will respond because AEP refuses to release their test protocol and data so that others can review it. AFAIK the only ones who have seen this data was a group from the IEEE who writes the standards for protective grounding. AEP talked to them in an effort to get their blessing. Didn't happen. One of the individuals on that IEEE committee spoke at a grounding seminar I attended last year and he pretty much implied that what he saw was just so much smoke and mirrors.

Another big utility, I think it was Georgia Power, also recently tried to do some testing to show that EPZ grounding wasn't necessary either. This was after they were cited by OSHA during hurricane restoration work a few years ago. Long story short, turns out their test method was based on measurements made while the "worker" was standing on the neutral. Their test setup was exactly the same as EPZ. And their test results confirmed EPZ theory.

To address the earlier question, there is no method of protective grounding that will prevent the possibility of step potentials occurring on the ground. Well you could create and EPZ on the ground but it would have to be so large that it simply wouldn't be practical.

[Hemingray Insulators]

If one of your crews are changing out a backyard transformer using a capstan, how do they stay 10 feet away from the pole ground? Do you cut it open 10 feet up the pole from the capstan?

my understanding of what he said applies to IF they GROUND the LINE to the pole ground, not under normal operateing conditions. unless you are refering to changeing out a pot with the primary denergized and grounds at the pole you are working...............????

[lewy]

As far as EPZ grounding goes Hydro One is among the 10 largest distribution & transmission utilities in norh america & they along with the EUS&A which represents the rest of the province believe EPZ is the perfered method of grounding

[wtdoor67]

You know there are about a dozen ways to measure a power co. Number of miles of transmission line, number of miles of distribution line, number of customers (of different types), amount of generation , etc. etc.

We need to come up with a criteria sometime. Gives a person a better perspective.

[500 KVA]

Glad to see your paying attention.

[BigClive]

When you think about it, every single job requires it's own EPZ/EPG assessment. This is where an actual understanding of the very characteristics of electrical current and it's preferred routes comes in handy. Unfortunately there are many workers who know "the job" but don't fully understand the nature of the beast they are dealing with.

For those who aren't familiar with the abbreviations...

EPZ = EquiPotential Zone. (Area bonded together to minimise any voltage difference across it.)

EPG = EquiPotential Ground. (As above but tied to ground.)