I’ve been training locators for over 20 years now, a good amount of that time having been spent training technicians outside of my own company. Seeing how a variety of different organizations handle similar tasks offers a lot of insight into the culture of my trade.
One of the things I’ve noticed over the years is how differently inductive locating is handled from one group to the next. As a quick review, a transmitter can be used to apply signal to a conductor in one of three ways: direct connection (conductive locating), close induction (use of the coupling clamp), and induction (also called transmitter induction or “dropping the box”).
The Common Ground Alliance Best Practices for Locating and Marking 4.12 places a hierarchical preference on active signal application methods ranking them in order of direct connect, then clamping, and finally induction, stating that induction “usually results in a weak signal that will ‘bleed over’ to any conductor in the area”. I’m already on the record as disagreeing with this particular Best Practice because it ignores the situational benefits of inductive locating which can make both clamping and transmitter induction better choices than direct connection on some locates.
I’m already on the record as disagreeing with this particular Best Practice because it ignores the situational benefits of inductive locating which can make both clamping and transmitter induction better choices than direct connection on some locates.
Culturally, the bias against inductive locating was made clear to me some years back when I was training a group of techs employed by a mid-sized contract locator. After discussing inductive locating as part of my theory lecture, I was approached on the next break by a manager who told me that his organization didn’t allow their techs to locate inductively. He followed up by telling me it was a fireable offense.
Another time, while performing field audits as a consultant for a small contract locator, I discovered a mislocate by a tech and called him back to the site to demonstrate how I was able to accurately locate the line using my coupling clamp. He watched me do it and then said, “We don’t have those. We locate everything by direct connect.”
While the clamp is an expensive accessory with limited applications, most transmitters can easily be used in the inductive mode on settings as low as 33kHz. Many multi-frequency sets include 82kHz or 200kHz which provide even better results, and for maximum utility in inductive locating, 480kHz transmitters are available.
What’s so great about inductive locating at higher frequencies? First, inductive locating allows for more flexibility in signal application since the user is not limited by the length of their leads or the availability of a physical access point. Second, the ability to place a signal at various locations along the linear run of a conductor can provide the strongest signal where it’s most needed, allow the technician to “steer” signal through areas of congestion, and because of the directional nature of the transmitter’s internal antenna, provide an opportunity to identify parallel conductors in some conditions.
Obviously, using inductive locating can cause problems, especially the misidentification of conductors due to bleedover. But the same high frequencies that cause bleedover onto unwanted conductors can also help identify conductors that might otherwise go undetected within the area of a locate. And the capacitance which lays at the heart of the bleedover problem is extremely useful in overcoming resistance in stubborn conductors.
In short, inductive locating can be a wonderful tool for tackling a variety of locating situations. As a private locator, I use it daily to locate lot lighting, irrigation controls, and power to outbuildings and sheds.
There are some great tutorials on inductive locating available on You- Tube, and your instrument manufacturer can provide information on how (and when) to use induction to get the most out of your locator. If you’re inclined to be nervous or hostile about inductive locating, I get it. But maybe it’s time to examine where it might fit into your organization’s damage prevention strategy.
Christopher Koch is a training consultant and President of ZoneOne Locating. He is past president of Nulca and worked on both the 2009 and 2015 revisions to the Nulca Professional Competency Standard. He can be reached by email at Christopherkoch@live.com or on Twitter @kochauthor.
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