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Incident Prevention Magazine

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Distribution Switching Safety

Lineworkers face no shortage of hazards during the course of a day, but switching is among those that give me the most pause. Opening and closing circuits, tying circuits together, breaking loads, transferring loads, tying or breaking substations – if any of these procedures go wrong, the results can be catastrophic. And while it always pays to heighten your awareness while switching, it is especially important to do so during the summer. Air conditioners, pool pumps, fans and other appliances add load in hot weather that can make any switching operation more precarious. In addition, the heat itself can cause the equipment to become overloaded. Regardless of the loads involved, there are safety precautions that should be taken every time you are switching. If you follow these basic ideas, the process becomes much less likely to go awry.

Communication
If you are switching as a crew, take extra time during your job briefing to make sure everyone understands the switching orders. Have the one-line available to show to crew members and ensure they have a grasp of what you are trying to accomplish. They need to know the route of the circuit, where the sectionalizing devices are, who will be positioned where, what the order of opens and closes will be and any other information pertinent to the process. And stay in constant communication as each segment of the switching is accomplished. Use repeat-back protocols so you know what you have said is understood and what you have heard is correct. If you decide to wing it, the best-case scenario if something goes wrong is an unplanned outage. Worse, equipment might be damaged or someone could be severely injured.

If you are switching alone, you should still work with a dispatcher or other functional authority. Make sure you are working from a written switching order and that you have read everything back to them and have it all correct. Then check your one-lines to confirm the tasks you are about to perform will accomplish the objective. While dispatchers usually have a great grasp of what is required, you are the person on the ground who has the familiarity with the part of the system you are on. If something doesn’t seem quite right, ask questions. Be sure before you begin.

Breaking Load
If it is possible – and by possible I mean that the switch is equipped with the proper attachment hooks, not whether or not it’s convenient – use a load-break device each time you open a switch. Few things are more disconcerting than being in your hooks 8 feet below an arcing switch that won’t go out. And if that arc manages to spread to the other phases, a hard hat simply isn’t big enough to hide under.

It’s also important to make sure you are familiar with whatever load-breaking device you will be using. Regardless of the manufacturer, they all tend to be two pieces with an inner tube that fits into an outer chassis. The inner tube must be reset after each use. This means it has to be completely seated into the chassis so that the contact tube and trailer (the moving contact assembly) reconnect with the trigger assembly. Otherwise there is no load-breaking capacity and the switch will arc if the load is great enough. You can confirm that it is reset by attempting to pull the inner tube out by hand. You should get resistance of approximately 20-27 pounds.

Another habit I recommend cultivating during load-break switching operations is to take downstream amp readings before opening a switch. This will let you know how much load is involved and whether the tools and equipment being used are properly rated. Load-break devices typically have an interrupting amp rating somewhere in the range of 600 nominal and 900 max. Switches and other sectionalizing devices will have ratings that vary by type and manufacturer. If you think the load might be approaching the upper limits of its range, take the time to verify. And just because you are familiar with your system and can remember that the line you are dropping had a manageable load in January, don’t assume that same amp reading is true in July. Hot weather can change everything.

There are load-break cutouts out there as well. One of the most common is designed with a self-contained load-break arc chute – we always called them “elephant ears” – that confines the arc and provides a deionizing action. So long as they are in good shape, these will do the job. But as they age they can lose their deionizing capabilities, and sometimes the chute falls off or breaks apart. If you encounter a switch that doesn’t provide for its own load-breaking – either because it is too old to have it or is damaged in some way – you should look for another place to break the load, either under oil or where there is a switch that will take the load-break tool. I have even gone so far as to hang a temporary switch that I could break load with in order to bypass the bad one. It’s not worth the risk of having a massive arc go off in your face.

Conclusion
There are many other factors that can come into play when switching, and especially when load-break switching. Multipot and capacitor banks, three-phase customers, enclosed overhead cutouts and underground circuits and switchgear can make a big difference in how a switching operation has to be carried out. Those things are beyond the scope of this article, but be aware of them. Regardless of the time of year – but especially in the summer – it’s important to sweat the details when switching. Be aware, be safe, be your brother’s keeper.

About the Author: Mike Caro, CUSP, is the HSE manager for Willbros Field Solutions. He has 26 years of industry experience, including more than 17 years of experience as a lineman. Caro is a board member of the Utility Safety & Ops Leadership Network and serves on the national leadership committee for the Utilities Practice Specialty of ASSE.

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