TEST 5 A MEASUREMENT OF THE INSULATION RESISTANCE (IR) GIVES ONE OF THE BEST GUIDES TO THE STATE OF HEALTH OF ELECTRICAL EQUIPMENT. THE RESISTANCE SHOULD BE MEASURED BETWEEN INSULATED CONDUCTORS AND EARTH, AND BETWEEN CONDUCTORS. AN INSULATION TESTER IS A HIGH READING RESISTANCE METER USING A HIGH TEST VOLTAGE – USUALLY 500V D.C. THE TEST VOLTAGE IS PRODUCED EITHER BY AN INTERNAL HAND-DRIVER GENERATOR OR BY A BATTERY AND ELECTRONIC VOLTAGE CHARGER. ATEST VOLTAGEOF 500V D.C IS SUITABLE FORTESTING SHIPS’ EQUIPMENT RATED AT 440V A.C. TEST VOLTAGES OF 1000V AND 5000V ARE USED FOR HIGH VOLTAGE (HV) SYSTEMS ON BOARD CHIP. THERE ARE SEVERAL MANUFACTURERS OF INSULATION TESTERS AVAILABLE BUT THE MEGGER TRADE NAME IS KNOWN WORLWIDE. TO PROVE THE BASIC OPERATION OF THE TESTER, SHORT THE TWO PROBES TOGETHER, SWITCH TO “M” AND PRESS THE TEST BUTTON OR ROCKERSWITCH. THE POINTERCHOULD INDICATE APPROXIMATELY “0”. BEFORE APPLYING THE TEST, THE EQUIPMENT TO BE TESTED MUST BE DISCONNECTED FROM THE LIVE POWER SUPPLY AND LOCKED-OFF ACCORDING TO STANDARD SAFETY PROCEDURES. A MEGGER TYPE IR TESTER CAN BE USED TO CHECK WHETHER THE CIRCUIT TO BE TESTED IS LIVE. SWITCH THE INCTRUMENT TO “M” AND CONNECT THE PROBES TO PAIRS OF EQUIPMENT TERMINALS.DO NOT PRESS THE BUTTON. THE METER WILL NOW INDICATE THAT THE CIRCUIT LIVE OR NOT. IF THE CIRCUIT IS DEAD IT IS THEN SAFE TO PRESS THE TEST BUTTON. CONFIRM THAT RELIABLE EARTH CONNECTION IS OBTAINED BY CONNECTING THE PROBES TO TWO SEPARATE EARTH POINTS ON THE EQUIPMENT FRAME WHILE TESTING FOR LOW RESISTANCE CONTINUITY
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