TEST 4 ALL ELECTRICAL EQUIPMENT HAS INSULATION. THE PURPOSE OF THE INSULATION IS TO KEEP ELECTRIC CURRENTS IN THE CONDUCTORS AND TO PREVENT CONTACT WITH LIVE WIRES. THE ELECTRICAL RESISTANCE OF INSULATION MUST BE HIGH TO PREVENT CURRENT LEAKING AWAY FROM CONDUCTORS. INSULATION RESISTANCE IS MEASURED BETWEEN: CONDUCTORS - EARTH AND CONDUCTORS. THE INSULATION RESISTANCE INCLUDES THE RESISTANCE OF THE INSULATION MATERIAL AND ALSO THE RESISTANCE OF ANY SURFACE DEPOSITS OF DIRT ,OIL, MOISTURE, ETC . SURFACE DEPOSITS CAN REDUCE THE INSULATION RESISTANCE. THE FLOW OF LEAKAGE CURRENTS THROUGH SUCH SURFACE DEPOSITS IS CALLED TRACKING WHICH IS ALSO AFFECTED BY THE CREEPAGE AND CLEARANCE DISTANCES BETWEEN TERMINALS. EQUIPMENT MUST BE MAINTAINED IN A CLEAN CONDITION TO PREVENT TRACKING AND TO MAINTAIN A HIGH VALUE OF INSULATION RESISTANCE (USUALLY AT LEAST 1M). INSULATION MATERIALS ARE NON-METALLIC AND HAVE VERY FEW OF THE GENERALLY GOOD PHYSICAL PROPERTIES ASSOCIATED WITH METALS. INSULATION IS ADVERSELY AFFECTED BY MANY FACTORS SUCH AS HUMIDITY, TEMPERATURE, ELECTRICAL AND MECHANICAL CTRESS, VIBRATION, CHEMICALS, OIL, DIRT AND, OF COURSE, OLD AGE.
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