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A minimum acceptable resistance value is usually specified (typically in the mega ohm (MΩ) range per circuit tested). Multiple circuits having a common return may be tested simultaneously, provided the minimum allowable resistance value is based on the number of circuits in parallel. Five basic isolation test configurations exist: [3]
An insulation resistance test (IR test) measures the electrical resistance of insulation by applying a voltage between two locations, and measuring the resultant current flow. Proper safety precautions must be taken when doing this test, such as exclusion zones, making sure no wires are exposed, and personal protective equipment is worn.
Megohmmeter M1101M. A Megohmmeter or insulation resistance tester, is a special type of ohmmeter used to measure the electrical resistance of insulators. [1] Insulating components, for example cable jackets, must be tested for their insulation strength at the time of commissioning and as part of maintenance of high voltage electrical equipment and installations.
The construction industry makes use of measures such as the R-value (resistance) and the U-value (transmittance or conductance). Although related to the thermal conductivity of a material used in an insulation product or assembly, R- and U-values are measured per unit area, and depend on the specified thickness of the product or assembly. [note 2]
The insulation of the cable plays a significant role in this. While paper-impregnated cables are particularly susceptible to external chemical and thermal influences, in high-voltage PE or XLPE cables the polyethylene insulation of the conductor is affected, leading to partial breakdowns and cracks that “eat away” the insulation.
The Comparative Tracking Index (CTI) is used to measure the electrical breakdown (tracking) properties of an insulating material.Tracking is an electrical breakdown on the surface of an insulating material wherein an initial exposure to electrical arcing heat carbonizes the material.
Basic insulation is any material added to protect a user from accidental contact with energized parts. Supplemental insulation is rated to withstand 1500 volts AC. Double insulation is a design concept where failure of one insulation system will not expose the user to a shock hazard due to the presence of a second independent layer of insulation.
Class II insulation means that the device is double insulated. This is used on some appliances such as electric shavers, hair dryers and portable power tools. Double insulation requires that the devices have both basic and supplementary insulation, each of which is sufficient to prevent electric shock. All internal electrically energized ...