Safety when working in presence of electricity is a universalgoal. Finding practical methods to achieve this safety, however, is notalways easy or obvious. Maintenance personnel must take the necessarysteps to assure that the system or portion of the system on which theyplan to work is in an electrically safe working condition. The accepted,reliable way to provide safety is to de-energize the equipment first,then to connect the equipment to ground so that it cannot bere-energized. Complexity of the electrical system normally determinesthe level of detail planning required for system clearing procedures.Complex power distribution systems that may have several sources into anarea require several switching steps to isolate a portion of the system.It is necessary to use more elaborate clearing procedures and writtenswitching instructions for systems together with a single-line diagram.The instructions and/or procedures should include verifying that thepower has been removed (by live line testing or other means) followed bythe placing of grounds and locking/tagging of isolating devices. Theclearing procedures should be completely written, checked and understoodby all persons involved before applying them to any portion of the powerdistribution system. This paper considers the subject from both Europeanand American points of view. It investigates the basic concepts anddefinitions to give prominence to operating bonds and to help theprocedure-project. It proposes some simple rules, a graphicalrepresentation and an algebraic model of electrical status to allow anauto-check of the clearing procedure
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