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GGcrossover wiringsurgeprotectorcircuitbreakerGsurgeprotectorprotecteddevicegroundsignal cablepower cablelightning surgecircuitbreakersurge protectorfor power lineprotecteddevicepowersourceTwo-wireGVUGcircuitbreakersurge protectorfor power lineprotecteddevicepowersourceThree-wireGWUVG9GroundingNot only surge protectors, but also computer systems and electronic instruments are connected to the earth grounding to prevent noise interference. Make the crossover wire thick and short to prevent a potential difference built up between the protectorʼs earth ter-minal and the instrumentʼs earth when the line is sub-jected by a precipitous rise of lightning surge.There are reports saying that only one instruments among many has been damaged because this one was left unconnected to the ground with a crossover wire after the connection had been taken out during a regular checkout (Figure 9-1).Insulation testBefore performing the insulation test for an instru-ment panel equipped with lightning surge protectors, you must disable the surge protectors because they will start discharging during the test and possibly cause insulation failures.With signal line protectors, simply unplug the element from the base socket.With power supply line protectors, remove all the grounding wires connected to the ground terminal. Be sure to re-connect all wires back after the test is completed.Molded-case circuit-breakerA power supply line protector usually incorporates a circuit protector, however, it may not be able to handle a lightening surge far exceeds its discharge withstand current rating such as direct lightning strike. Be sure to set a molded-case circuit breaker. Choose one that its current rating is equivalent to the max-imum load current of the surge protector (Figure 9-2).Surge protectors for power lineMaximum load current up to 200 A is selectable. Single-phase/two-wire, single-phase/three-wire, three-phase/three-wire and DC power supply systems are selectable. Choose one based on the load current and the number of phase.Points of caution when installing surge protectorsFigure 9-1Figure 9-2

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