PURPOSE: To easily discriminate a live line from a dead line through a cover, by a method wherein a liquid crystal element is operated by the voltage difference between AC voltages induced in respective current collection plates when AC voltage is applied to a plurality of cores of an insulated wire.
CONSTITUTION: A current collection plate 3 and a current collection plate 4 are different in a geometrical relative position with respect to three core wires 1a, 1b, 1c. Now, when symmetric three-phase voltages are applied to the core wires 1a, 1b, 1c, voltages different in a phase are induced in the current collection plates 3, 4. By operating a liquid crystal display element 5 by applying both voltages to said display element 5, it can be displayed that a three-phase insulated wire 10 is in a charge state. The difference voltage appearing between the current collection plates 3, 4 is different by the relative positional relation between the current collection plates 3, 4 and the core wires 1a, 1b, 1c. When the mount positions of the current collection plates 3, 4 are successively rotated by 360° around the core wires symmetrically arranged of the three-phase insulated wire 10, since the max. value appears at every 60°, the areas of the current collection plates 3, 4 are selected so that the min. value of said difference voltage becomes sufficiently larger than the min. operation voltage of the liquid crystal display element 5.
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