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Thread: Why couldn't the "high end" 3M Dynatel 7573 locate energized conductors in concrete??

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    Default Why couldn't the "high end" 3M Dynatel 7573 locate energized conductors in concrete??

    Hello everyone. This is my first post on this forum. I am the owner of an Industrial Electrical & Telecommunications Contracting company. We recently invited 3M to come out and perform a demo of their Dynatel 2273M and 7573 utility locators. These are their "high end" models that also read & write to their marker balls.

    But first, a little background info: My company recently started providing concrete scanning services (GPR) due to that fact that most of the facilities we work at require a GPR scan prior to drilling through concrete walls and floors. Being able to perform this service "in house" will save us time and money. Additionally, we can offer these services to other contractors and develop another revenue stream. When performing a GPR scan, it is always a good idea to use a utility locator in passive mode as a secondary means of identifying electrical conduits and/or wiring in the area (energized only). Sort of a double check. We've been using our el' cheapo Greenlee BLL-200 Buried Line Locator for that purpose, however, it has no gain adjust knob, which prevents me from fine tuning (it becomes overwhelmed when there are multiple conduits in the area). As a result, I decided to purchase a "real" utility locator. I decided on the 3M solution because I thought that my customers might be interested in using marker balls around their facilities. And I thought for sure that a $5k-$6k utility locator's passive mode would outperform my $1500 Greenlee........I was wrong.

    So the 3M rep came out and showed us the 2273 and the 7573 along with all their bells and whistles. We went outside and did some direct connect and inductive. But then I asked him to bring it inside my warehouse where I know I have energized under-slab conduits. He put it in passive mode and could not locate them. He tried all three passive modes and then tried the other locator (and the result was the same). So I got out my Greenlee and immediately located them. Then we went outside in my back lot where I knew of some underground conduits, and both of his units located them perfectly (in passive mode).

    Do any of you have any idea as to why the 3M locators could not locate energized conductors under a 6" slab, when my Greenlee BLL-200 could? And secondly, is there another type of locator and/or tool that you would recommend for detecting energized conductors within or under a concrete slab? The slabs we typically deal with are 8" to 12" thick.

    Thanks for your help!
    Brian

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    Default Re: Why couldn't the "high end" 3M Dynatel 7573 locate energized conductors in concrete??

    Hi Brian,



    It looks like you are just doing a passive sweep which can be accomplished by setting the Dynatel(TM) locator to LF mode and changing the antenna mode to Special Peak. This will search the widest range of frequencies and using the Special Peak antenna will allow the unit to be sensitive with Spl Pk.

    This would be the closest to your current solution.

    From your description it looks like you tried 60 Hz, 60L and 60H which are all power harmonics and require current to locate. This means that any power lines without a load would not be locatable until a load was applied. Having voltage potential does not mean current so you may need to plug something in.

    A passive LF or Radio sweep can be done but one challenge is that you rely on radiated emissions from other sources. There is simply no guarantee that this will be consistent or measurable. I would suggest applying your own signal with a transmitter.

    Best regards,
    Gary Morris 3M(TM) Tech Service
    512-653-8203

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