Recent Damage....

[Mke]

Ok. So here is the situation. Old Road Easment through an active Airport. Old direct burried Concentric Neutral Primary with aluminum wire installed in the mid 60's. The only access for this primary is a "dip" pole about 1200' away or a underground transformer about 900' away. This wire parallels two duct banks (one only parallels for 700' and the other goes most of the distance, but both are over10' from the line) as well as multiple old abandoned utilities (4" water, 1" steel gas, and an old direct burried phone line) most of the distance. The Damage took place about 4' south of another line crossing this line at an angle.

They are installing a new feed to replace this feed. While doing the trenching they hit this primary. No one got hurt and not facilities are out of service except what this primary is designated for.

Here is the Kicker, my paint is 4' off. I should qualify that by saying, " the primary was 4' from my paint". The difference being that there is a signal where my paint is. I verified this several times.

Here is the thing, I know all the steps I did in the original locate were correct, and that if that primary would locate I would of located it. I won't go into all the steps I did, mostly because I don't want to give the green horns around here any ideas that would go against most companies policies. I will let you know that Ringed clamped the primary in both access points. I also used 3 different pieces of equipment on the original locate, which included the 810, Split box, and a 60cycle. All of which gave me a peak or null depending on the equipment right in the area of the line I located ( within a foot of the mark).

Any Opinions on what the hell happened?

Fortunately (knock on wood) no one is busting my balls, but all I can think about is, "if this has happened once, it can happen again".

and for some more ground work, my 810 just came back from calibration, it is a single high frequency transmitter so I can't change to a lower frequency, and I was dead nuts on on all the rest of the crossings in that trench. And the most glaring fact, yes I did induce the primary. And If I get some flak for that I'm ok with it.

I'm not sure if its the type of primary that is the headache, or if it was the close proximity of a better conductor.

Feel free to ask more questions if clarification is needed. I'm just trying to figure out if there was something else I can do or even a piece of equipment that could help out in this situation.


Thanks for any input

Mke

[Utilitrack]

Mke-
Was the concentric neutral in good shape? The iisue that I have seen with these is twofold 1) the neutral deteriorates over time leaving your high frequency transmitter no other option other than to bleed off onto another nearby conductor or groundwater. 2) the whole rub with these types of cables is that your tone runs on the neutral which is direct contact with earth so signal goes to ground all along the run VERY quickly making locating for any distance VERY difficult. Not sure why the 60 cycle confirmed your mark out, i assume that there was something buried there though. DB concentric neutral primaries are tough, we usually get the power company to come and open up the transformer so tha we can clamp around the cable trying to force signal onto the actual conductor rather than the neutral. I feel for you.

[headcipher]

Metrotech 850. We primarily use 810's and 850's for our locating. I've run into similar situations before and 99.9% of the time all that I've needed to get that line right is the good ol' 850.
Of course, there has been occasions where it just wouldn't give me the signal where the primary really was, and so far in all the new machines I've personally tested the Vivax was the most accurate with these problem spots. I've even compared it head to head with the RD8000 and the i5000, and while these are really awesome machines, the Vivax accurately found the deep/poorly grounded/super congested primary I needed. I just wish it was as light as the RD.

[ProfessionalLocator]

The bare concentric neutral deteriorates and after years, depending on the conditions in the dirt around it, becomes useless for locating purposes.

I had one just like this. When the damage was exposed I picked up pieces of the concentric neutral, it crumbled in my hand like old, dry leafs.

The one you marked has been in the ground around 50 year and likely the neutral was largely corroded away.

As for the 60 cycle matching your marks you need to test pit and see what's down there giving you that signal.

[Turk182]

Old aluminum primaries can just plain suck in a huge way as far as signal goes. I had one last winter where the power company was replacing a three phase primary for a municipal well pump, I marked out the power and the next day get a call for an incomplete for that ticket, I go there, and my marks are off by two feet. I hook back up to the transformer and my signal is still on my original marks, I hook up to the dip pole and the results are consistent with my original marks. The power company hooks up their equipment to the pole while mine is hooked to the transformer, and we both get signal only on my original marks, which are two feet off the actual potholed three phase primary. I had another locator come out to the site with a brand new piece of equipment, and the signal still peaked and nulled on my original marks, but there was absolutely nothing there.

[Danger]

My question is this... have you potholed it where it crossed the other utility to find out how close in proximity they are? I have a project with I get signal jump really bad from one utility to another... when I finally uncovered it... I found that the one was laying directly on top of the other which was a better conductor... luckily I had a patient crew and we took the time to find all the utilities, and had no damages....

[big boots mcghee]

Or, as another alternative, could that primary have been spliced and rerouted some years back with another piece of concentric neutral primary? Maybe your signal stayed on the old, abandoned piece? At times I've gotten better 60 cycle tones over abandoned primary than on the energized pieces nearby.

[headcipher]

Ditto, BB Mcgee. I've had the same thing.

[Mke]

Well, this is what i'm thinking.....

Due to the condition of the primary (Old and deteriorating, our ground water is at about 2'-3' most of the year) and the fact that it plays tag with the other mystery line (which I believe is the old steel gas line), it is overshadowed by the other line. I wanted them to expose the other line, but water level is high and they would of had to bring in a pump to get the water out of the ditch. It was bad enough they didn't even try to repair the line that was damaged. They are just waiting till the new line is installed. As I told my boss, " if it was locateable, I would of located it." No one is pissed or anything, but it drives me crazy because out of the 20 something utilities crossing their trench, There is only 4 live ones, and I missed one of them. No body cares that i'm DNO the other 20. Hell, I even located the 6' storm line right on the money and that wasn't even locateable.

As for the 60 cycle i'm using, its the Power Pup from Aqua-tronics and she does real good. This time she was giving me a peak and null over from where the 810 gave it... but only by 10" or so.

Thanks for the info guys.... I'll see if I can upload an arial to show you.

Mke

[locator00566]

Pipe Horn

[nrp3]

I am assuming it makes a difference locating ones that are insulated versus not? I know that the utilities have had problems with corroded neutrals causing power to flow through the earth instead of through the cable causing some electrocutions, scary stuff. I wonder if this was part of it, I may have missed whether this line was live or not.

[Danger]

Hey it happens to us all... I had a gas service damaged today... I have located that stretch of road countless times now and even spotted the 4" MP yesterday... I never once picked up a signal on that gas service... and the house it went to... the access to that house was on a neighboring street and there was a 2" MP supplying the neighborhood. then you add to it.... the house can barely be seen from the street where the gas main is... the investigator and I stretched a tape ( it went under a fence and through the woods) and it was 200' from the main to the meter... and let me add... you could not get a signal on the trace wire at the meter.... the 2" MP gas main on the road that the house is on... was 60' away from the house.... who woulda thunk it? I luckily didn't get dinged for it...

oh yeah... let me add.. the gas main had been pipe horned by 2 locators with a hell of a lot more experience then I have... and they never picked it up on a sweep...

[daman1]

One of the first things I was told when I started locating was that this is NOT an exact science. You can only mark where you get a signal. Somewhere along the line, companies started promising 100% accuracy. It can't be done. It could be anything but I'm thinking Bigboots and Danger may be right. You'll never know for sure without pot-holing it and you'll probably get a different answer each time you do it.

[FailedSafetyAudit]

I saw you mention that you used a power passive 60hz cycle, did you consider trying a radio passive sweep? Did you consider trying to direct connect to the ground wire on the pole that was 1200' away? Never heard of a power pup or aquatronics, you should trying getting a Radiodetection C.A.T. (Cable Avoidance Tool) as they are kick ass good. It's a passive only wand that supports power and radio passive. Just as the line locating abilities of the metrotech 810 are legendary, so are the passive modes offered by Radiodetection.

You can only mark where you get a signal. Somewhere along the line, companies started promising 100% accuracy. It can't be done.

This, is true.

[Danger]

well, my groups motto is this... when in doubt... dig..... I don't like digging any more then the next guy.... but you will never be sure until you put eyes on it....