The Mystical Yellow Reel

Ever wondered what the yellow spool of wire that comes with the Radio Detection locator is for? Well, the following might just answer that question.

Here is another tip that may make a difficult locate a little easier. We all know the importance of proper grounding of the utility and the difficulties associated with poor utility grounding. This technique helps to over-come these situations and provide a good circuit that we can use to locate our target line.

The main utilities where this technique can successfully be used is with, metallic water or gas mains. Often these utilities are installed without any sort of insulation material or coating, or this coating may have been damaged during installation. In this scenario it is difficult for our signal to travel along the target line before it wants to return to the transmitter. Remember that the amount of energy that leaves the transmitter MUST return to the transmitter, and this will always follow the path of least resistance.

One method of overcoming this problem is by using what is called a “double ended connection”. For this to work you need at least 2 access points for the target line. With water mains this can usually be easily achieved by accessing two fire hydrant connection points. Gas mains can be a little more difficult because often the access points are often spaced at a greater distance than the hydrants for your typical water main installation, these are usually no more than 80 meters apart.

So how do we go about establishing a double ended connection. Firstly, connect the transmitter, via a direct connection to the first access point. Out of habit, I usually use the red lead to connect to the utility, then the black lead with the addition of the extension cable is connected to your target line at the utilities second access point. A complete circuit is achieved without using ground as a current return path. The long cable should be kept as far away as possible from the expected route of the line.

This method of applying the transmitter signal is ideal for positive identification of a target line. When a connection has been made to two points on the same line, the same level of current should be detectable around the circuit. The locator display should remain constant as long as the depth of the target line does not change.

Locating Unlimited Pty Ltd (RTO ID 45518), Australasias leading provider of Underground Damage Prevention and Locator Training is committed to providing training and information to help maintain safe work practices around buried utilities and prevent damage to this infrastructure.

 Contact Jeff at Locating Unlimited 0419 44 66 27 or jeff.moore@locatingunlimited.com.au



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