38 replies to this topic

[Utility Innovations]

Hello Grimple, I am not sure we we met before (getting old) maybe you could send me an e-mail to refresh my memory at info@utilityinnovations.com.

As for your question, here is my take on it.

Bracket grounding does not provide protection when you are a few spans away from the grounds and the line becomes energized from an operating error or a live conductor making contact. Bracket grounding 2 miles apart will provide protection from induction and backfeed from small generators. Because equipotential grounding is difficult (impractical) when removing old conductor, raising new conductor and during a large planned outage with lots of crews and work on every pole, bracket grounding could provide protection if, extra steps are taken to guarantee that there is virtually no risk of accidental reenergization. This guarantee would need to be planned, written down and approved as an exception to the mandatory equipotential grounding method. Extra measures such as removing a span of conductor, removing loops and risers may need to be taken.

The above would be a procedure violation in many organizations and would need to be approved. The same organizations that do not approve an exception to bracket grounding sometimes allow the high risk practice of taking a line out of service (because the job cannot be done safely live line), not grounding, but treating it alive by using rubber gloves to do the job.

Wayne

[pops]

so you are saying that if my grounds are 2 miles away i'm protected from induction, but not if the circuit is reenergized? how does THAT work, wayne? arsch[1].gif pops

[mrgrowl791]

O a reconductor job, say 20 spans, and you have two phases laid out to the road and one phase laid out to the field in fiberglass aux. arms .and your new conductor is pulled in when you start clipping in, what would be the proper placement of equip. grds?? would you put a set of grds at the takeoff, move 4 or 5 spans put up another set, another 4 or 5 spans add another etc.. Then could you just move the cluster bar to each pole and grd it to the nuetral?? If you do this technically would this be considered an energized pole with grds install??

[three]

The reason your'e not protected if the line is energized is because the ENTIRE line becomes enegized. A lot of people have the missnomer that electricity will only reach the grounds, and then seeing a path to ground, it will dissipate at that point.

This couldn't be farther from the truth.

The entire line is energized at the same time. You could put 100 sets of grounds on and if your'e on the pole working in leathers, and the line comes hot, your'e not protected at all. Your'e only another path to ground.

By using grounds only the only thing you can hope to acomplish is to blow a fuse or trip a breaker. That is if your'e not so far from the sub that it only sees it as load.

By using an equipotential grounding cluster on the pole you are working on, you put yourself at the same potential. You should mount it as close to your feet as possible to assure that you are within the field. It is a pain in the @ss to use, and you have to set it up at every pole and go through the whole procedure of grounding it each time. But I truly believe it will save lives.

Sorry if I talk too much.

[mrgrowl791]

So you can't go three four or five spans apart?? The cluster and the complete grd set must be installed on every pole? TexasLineworker, doesn't Irby use equip. grds ?? How do they use them on a reconductor job??

[mrgrowl791]

Going back to my original question , technically, with the aux. arms and energized conductor laid in them, you would have to cover up the energized phases and wear rubbers with the grds installed. Would wearing the rubbers do away with the equipotential grds even with bracket grds installed. I guess what I would like to know is what would the correct procedure be for this situation?

[three]

I'm not really sure on that mrgrowl. From what I've been told the purpose of the equi. potential brakets is to put you at the same potential as the pole and line. Not sure if wearing rubber gloves would mess that up or not.

Are you having to work this reconductor job off the pole?

I've had to do a few myself. What we did was find some way to kill the old line. Do some switching or take an outage for a bit. Then lay it out and hang the dollys and ropes. Then switch it back if we had to. Keep the new conductor grounded while we strung, and clipped it in. You could set up the equi.potential grounding stuff up while tying it in. In these situations I prefer using conventional tie wires. It's a lot easier to keep control of my tails. Then when everything is bumped over, let the old wire down at the deadends, and take a set of long hot cutters up the pole and cut the old wire at the layout arm. Right at the arm, so that the ends wont flop up into anything.


Of course sometimes there's stuff below that it can't land on so you have to rig up something else. Like a chainsaw or a bulldozer in front of a bucket truck!! yes way

[mrgrowl791]

Outage is probably out of the question.(many active oil wells working).There is no back feed. What about working the poles out of a bucket? Would the equip. grds need to be set up on every pole?Plus we armor rod and then tie in with 11' piece of tie wire.

[three]

I'd say if your'e working out of a bucket set some grounds up, cover everything that's hot, and wear your gloves all the time. The equi. potential stuff wouldn't protect you in an insulated bucket anyway.


Just work it all like it's hot. brewsky

[mrgrowl791]

Thanks. That's what I thought also.

[pops]

Mr. Three, I understand completley how grounding works. My problem is with this reply from Utility Innovations:

"Bracket grounding does not provide protection when you are a few spans away from the grounds and the line becomes energized from an operating error or a live conductor making contact. Bracket grounding 2 miles apart will provide protection from induction and backfeed from small generators."

The reply suggests that there is a difference between a reenergized line and a backfed or induced line. How does bracket grounds two miles apart protect me from backfeed or induction but not from the line being reenergized? It doesn't protect at all.

[Utility Innovations]

I guess I owe an explanation. My understanding of grounding practices comes from being on study committees and writing directives and procedures since the late 70,s. Admittedly knowledge re proper grounding of lines has been in a state of change forever. Also there is no doubt that the safest grounding method is equipotential grounding at every structure. However, as I understand it there is a difference between a reenergized line and an induced line (along with backfeed from a small portable generator). The electromagnetic field from an a-c power line causes two kinds of induction; an electric field (capacitive) induction and magnetic field (inductive) induction. Proper grounding and bonding will control, but not eliminate, voltage and current induced on isolated circuits.

A nearby power line will induce a voltage on a nearby isolated conductor. There is no current flowing in the isolated conductor if the isolated conductor is not part of a circuit. One set of protective grounds on an isolated circuit will collapse the voltage due to electric field induction. If a worker was to get between an isolated conductor and the earth, the exposure to the high induced voltage combined with the relatively small amount of current available could be fatal.

A nearby power line will induce current on a nearby isolated conductor when that conductor forms part of a circuit. Grounding a conductor on each side of a work zone (bracket grounding) will create a circuit through the conductor, down one set of grounds, through the earth and back up the other set of grounds. The first set of grounds installed on an isolated conductor will collapse the induced voltage from the electric field, a second set of grounds will create a circuit which will cause an induced current to flow from the magnetic field.

When bracket grounds are removed, the first set of grounds removed will open the circuit and interrupt the current flow. An immediate voltage will appear (recovery voltage) across the gap between the ground clamp and the conductor. In high induction areas a long arc could be drawn. When there are more sets of grounds installed along the line, it will be the second to last ground removed where there could be a long arc drawn.

Once bracket grounds are installed, the conductor between the two sets of grounds will have very little induced voltage but could have a high electrical current flowing through it. When grounds are installed at a work site (between the bracket grounds) the work site set of grounds will have relatively very little current flowing in it. The middle set of grounds creates two circuits for the ground current to flow where previously there was one. The current from one circuit goes up the middle set of grounds and the current from the other set of grounds goes down the set of grounds. The two currents tend to cancel out and, therefore, very little current flows in these grounds.

When working on an isolated circuit, protective grounds on the circuit will reduce the voltage due to backfeed from a small portable generator to an acceptable level. The transformer impedance and the resistance of the conductor between the grounds and the generator will probably not create a large enough fault current to cause the generator to overload. The generator will keep running, the grounds will bring the voltage down to a safe level, but there will be a current flow in the conductor. Because there is always a chance of current flow in a conductor, the conductor should not be cut or joined without first installing a jumper.

Backfeed from larger industrial or commercial generators would cause higher voltages to appear on grounded conductors at the work site. Large generators are more likely to be installed and inspected properly, so backfeed is very unlikely. The hazard from backfeed is from the unknown generator.

Meanwhile, while I am writing this I am thinking that I need to research this a little more. avatar233[1].gif say what

Wayne

[mrgrowl791]

TLW, you mentioned a travelling grd when you're pulling in the new conductor. Do you use the equipotential grd mats around the stringing equipment? The travelling grd to the main line nuetral and the equipment? Would the mat be tied to the equipment? Also, would rubber gloves defeat the purpose of the mat? What about dielectric shoes?

[BAS]

I work for Allegheny Power (maybe soon to be a part of First Energy) and we have to equipotential ground at each work location unless we ground on each side of the work area and eliminate any/all possible sources of backfeed/energization. Equipotential is a pain unless you are going to be up the pole for extended period of time. I'd rather "shunt ground" each side of my work location.

[wood stabber]

EPZ is a pain I totally agree but I can testify it works,,,, take the extra time and put up the band and go home at night!

[Bipeflier]

Good reference book. It is also available free in hard copy for the asking.

CHANCE Grounding Encyclopedia

[Manitoba PLT]

The Safety rules regarding EP bonding in my area:

Ep bonding is required in addition to temp working grounds on 66kv and below if any of these conditions apply:

-If you do not have two open points (a float installed and a fargo(hot line tap) removed)

-Cannot maintain adequate clearance from adjacent lines.

-Sources of induction are present

-If Low voltage sources of back feed cannot be eliminated

-If lightning is probable or occurring in the area