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24 I ICT TODAY HOW TO TEST THE BONDING CONNECTION When testing a bonding connection, it is useful to think of busbars as the window to the soul for the rest of the room. They should be inspected first for potential problems, such as loose connections. The first step is to test for ac and dc current. From there, make it a priority to determine the ac and dc current measurements. The ac current measurements are necessary to pinpoint areas where outlet wiring is not compliant. The dc current measurements are made to track corrosion sources and/or failing power supplies on uninterruptible power supply (UPS) units, routers, switches, and other equipment. Then, utilize the two-point test method to verify the bonding effectiveness. This requires the use of a micro-ohmmeter connected between any two points to verify that the resistance between those two points is less than 100 milliohms or 0.1 ohm. A common best practice is to test from the busbar to the furthest point in the room. Most of the connection points between busbars, rack, tray, and other components should and will be sufficient, but there is always a possibility that there will be that one loose connection that makes the extra effort of testing all the more worth it. Also, do not forget that micro-ohmmeters have greater resolution and are a fraction of the cost of earth ground testers; unfortunately, earth ground testers are what most technicians are still using today. Use a half-step method that starts at the half-way point of the connec- tions. Then, test from that starting point down the line, which will narrow the scope of observations and more easily pinpoint the source of a fault. BONDING AND GROUNDING 2.0—A BETTER BEST PRACTICE What is it about the things taken for granted, after all? Just as the story of Benjamin Franklin flying a kite in a thunderstorm endures because of its literal flight of fancy, has it not also become a figurative lightning rod for why it is important to dispel rumors and myths when the story becomes too fantastic for its own good? FIGURE 4: A graphical representation of a mesh bonding topology or series-parallel circuit with many parallel paths with interconnections and an overall resistance of just 2.8mΩ . For many years, the best practices of bonding and grounding have been a series of educated findings that allow everyone to benefit, build upon, and follow suit—making small modifications along the way and always working to improve upon what has come before. Pertaining to bonding and grounding, this has meant holding on to the accepted understanding that parallel paths never really meet until they reach the busbar, thereby resulting in all circuits relying on just one main connection to that busbar. The inherent difficulty that emerges is the fact that there can be different gauge effects and loose serial connections that result in different potentials between the runway and the rack bonding systems. From this perspective, when searching for new ways to bond cable runways, racks, and cabinets that minimize labor and controls cost, it is wise to pursue a system that helps industry professionals meet project requirements, improve everyone's overall fundamental understanding of bonding, and more easily accept and adopt improved best practices when they arrive, while looking for ways to improve upon what has come before. ICT professionals must also work to ensure that any fundamental changes in the field can be easily taught and learned or the industry risks losing a better best practice to the fringes of progress. Perhaps one of the best practices is that of the mesh bonding topology, which uses a series-parallel circuit rather than multiple series-bonding circuits (Figure 4).