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SR20 Not seeing buried power

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  • SR20 Not seeing buried power

    I've been using the SR20 for a few years now and I ran into a situation that is causing me to have concerns about whether or not I'm providing good info to our customers:
    I was scanning at a location where I know for a fact there are 3 large buried power conduits (PVC ~4" at about 2'). I know exactly where they are because I was there when they were put in and I have pictures. Each line was pulling 4,5 and 2KW, respectively, during the 60Hz scan. Lower right was at about 1800 and it wasn't maxed. The only signal I picked up was about 2' away and parallel. I believe this is an old exterior light run. The 3 power mains didn't show up on any scan (60Hz, low/high freq, omni). If I ping ground I can trace it. However, that isn't always an option.
    My concern is that if I'd been doing this for a customer, with no pre-existing knowledge or access to transmit on ground, I'd never have seen it and someone could have gotten seriously hurt or killed. Any thoughts on why it wouldn't show?

  • #2
    time to get out the dowsing rods,
    Push sticks/blocks Save Fingers
    ~~~~~~~~~~~~~~~~~~~
    "The true measure of a man is how he treats someone who can do him absolutely no good."
    attributed to Samuel Johnson
    ~~~~~~~~~~~~~~~~~~~
    PUBLIC NOTICE: Due to recent budget cuts, the rising cost of electricity, gas, and oil...plus the current state of the economy............the light at the end of the tunnel, has been turned off.

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    • #3
      No locator made will pick up the lines if there is not a good big draw going through them the bigger the better. Also some types of wire that was used for power lines is very bad at showing up on a locator and even though it can show up on the bad cables you really need a large load to do it. The seektech sr -20 has 60hz on the menu by default but there are 2 other 60khz entries that are disabled in the menu if you do a lot of power locates you need to enable them so that you have the choice of trying all 3 when doing power locates. They are 60hz but they have a different little number after them that stands for harmonics, 60-7, 60-9 etc all the other locator companies just give you one choice period and you need all 3 enabled. Once you start using all 3 you will find most power lines that have a good load going through them, the signal may be distorted on the screen but they will show up enough to mark.
      Seattle Drain Service

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      • #4
        One more thing to add the whole harmonics thing is just multiples of 60 for instance 60-2 =120 60-3 = 180, 60x4 = 240 so in really bad times I have had to enter by hand my own number on the seektech to get a better signal but it is always a multiple of 60. Modern big motor drives on pumps and chillers are VFD motors (variable frequency drive) and they change the frequency at start up and normal running but they leak backwards onto the supply lines and any other conductive items in the area like gas tracer wire, metal pipes etc and try to ruin any kind of locate you are doing in the area and that is where harmonics comes in, this is a modern thing that locators of the past did not have to deal with and I am glad seektech gives me a shot at it.
        Seattle Drain Service

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        • #5
          Another thing (sorry) but sometimes when another conductor is in close proximity to the target you are trying to find it will just plain be the one that you find and then you have to use other means, Radiodetection and Vivax sell a direct connection lead set for power lines to a transmitter but now you have to make a connection not just a passive locate. Or vivax now sells a spar 300 which is a locator that does not need to be directly over the target line so if an old power line is on the right side you move over to the left side of what you are after and can get a signal. Or GPR ground penetrating radar to find the conduits. Close proximity to other lines is always tough.
          Seattle Drain Service

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          • #6
            something else to note. if 2 of the 3 are running in the same phase and those 2 are just about equal in amps drawn to the single line, the instrument will have a problem locating the lines. It's because there is a cancelling effect of the signal.
            ~~

            ... it was plumbed by Ray Charles and his helper Stevie Wonder

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            • #7
              Maybe.. do you need upgrade a new firmware?

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