Issue link: http://read.dmtmag.com/i/131533
68 • JUNE 2013 • WORLD FENCE NEWS To start this article off I'd like to set a little background. At one point, I was managing an access control division for a wrought iron company, and 50% of our repeat service calls on brand new gate systems were because of inductance loops. It was frustrating to see our profit margin get consistently eaten up by repeat service calls, so I began to look for a reliable loop solution. After trying different wrapping techniques and materials, and most of the products that were on the market at the time, I decided that our best bet would be to design our own loop. BD Loops got started a little over 10 years ago with the intent to improve the design of the inductance loop. What we discovered was that the gate and door industries were riddled with bad science and myths where inductance loops were involved. There were misconceptions on every aspect of inductance loops from what type of material causes a detection, in which direction the wires should be wrapped, whether or not lead-ins should be twisted, if it was ok to run lead-ins under the gate path, if splices were allowable, where loops should be placed in reference to a gate or door, and what sizes loops should (or should not) be. Myths and facts about saw-cut loops BY TED DICKSON , OWNER , BD LOOPS Running into all these myths about loops was both amusing and frustrating; inductance loops are really very simple, but all the myths made them appear complex and difficult to understand. To splice or not to splice, that is the question Shortly after coming out with our direct burial loop we were asked to design a saw-cut loop for existing roadways. The first myth we ran into about saw-cut loops was that the loop could not have any splices in it. We discovered the reason behind the splice myth is that the splice has to be watertight and have a good electrical connection. If either of these requirements are not met – the loop would likely fail. Unfortunately not all installers carry around a soldering iron and watertight splice kits, tools that are necessary to make the best possible splice. There are a few simple rules that need to be followed to create a splice. Only splice, add length or repair a damaged loop lead-in; do not attempt to repair a damaged loop or add length to the loop itself. All connections absolutely must be soldered. Soldering creates a strong electrical connection in many ways, including preventing corrosion and oxidization of the wires after a short time. Use a watertight splice kit; these can be purchased through many distributors or electrical supply stores. Do not use electrical tape or nonadhesive lined shrink tubing to cover your splices. Watertight splice kits are more reliable and more likely to stand the test of time. Lead-in: twisted or untwisted? The second myth we ran into was that the loop lead-in has to be twisted between 3 to 8 twists per foot or the loop lead-in would not "cancel" and would detect a metal object above it. We spoke with several individuals who were certain that lead-ins run under gates and had resulted in the gate being detected as it tried to close. A major reason this myth got started is when an outside loop lead-in was run under the gate path, false detections would be attributed to the gate being detected by the untwisted leadin. This kind of issue is common when an installer uses a blade that is too narrow, such as a 1/8" blade. Installers often choose to use narrower blade sizes because they are less expensive, easier to find, and cut faster than wider blades. Unfortunately, 1/8" grooves are too narrow for sealant to flow around wrapped wires and fully encapsulate the wire, which forces the installer to lay the lead-in wire on top of each other with no twists. This leaves an air pocket which allows the lead-in wire to move ever so slightly in reference to the other wire. This slight movement will result in false detections; the movement can be caused by ground vibrations from nearby traffic, trains, or even the gate itself. To correct this problem the installer cuts in a new loop and uses a wider 1/4" blade or doubles up 1/8" blades to cut the lead-in run and twists the lead-in. The problem goes away – so the installer believed that twisting the lead-in was necessary to "cancel the fields" or prevent the gate from being detected. What is really happening is the continued on page 70 Isn't It Time to Put the Strength of the Gorilla to Work for Your Business? Fast Installation, Water-Shedding Designand Now ICC Compliant... 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