Cable Megger Test Insulation Resistance Values Table

Based upon equipment rating.

Cable megger test insulation resistance values table.

Since 80 of electrical maintenance and testing. Go no go minimum acceptable insulation resistance value go no go testing is performed on new cable installations to determine if the insulation has been damaged during installation. If insulation resistance of the cable is found between 1000 and 100 kω km at buried temperature the subject cable should be replaced urgently within a year. Reverse side of card at right is used to record the test data.

Figure 3 typical scale on the megger insulation tester. Comparing this result with the correct row of table 2 shows that our cable passes the insulation resistance test. A megger is an ohmmeter that measures resistance in the megohm scale. The first thing to check is the cable testing environment and cable preparation.

1k v 1 mω minimum 1kv 1 mω 1kv. A rated line to line voltage for three phase ac machines line to ground voltage for single phase machines and rated direct voltage for dc machines or field windings. Figure 4 typical record of insulation resistance of a mill motor. The megger insulation tester is essentially a high range resistance meter ohmmeter with a built in direct current generator.

The procedure of insulation resistance test or megger test are given below. First we will disconnect all the line and neutral terminals of the transformer. Curve a shows test values as measured. Hands down without a doubt one of the most universally searched topics on ec m s website from a historical perspective is insulation resistance testing as a result some of our most popular evergreen articles like understanding insulation resistance testing continue to top the charts when it comes to most popular content.

B kv is the rated machine terminal to terminal voltage. Megger leads are connected to lv and hv bushing studs to measure insulation resistance ir value in between the lv and hv windings. One meg ohm rule for ir value for equipment. The minimum acceptable insulation resistance value is calculated using the following formula.

As per ie rules 1956. It s also known as an insulation tester. Curve b shows same values corrected to 20 c see page 22 giving a definite downward trend toward an unsafe condition. Values based on ieee std 43 2013.

At a pressure of 1000 v applied between each live conductor and earth for a period of one minute the insulation resistance of hv installations shall be at least 1 mega ohm or as specified by the bureau of indian standards. Ansi neta mts 2015 table 100 11 insulation resistance test values rotating machinery for one minute at 40 c. For good insulation the resistance usually reads in the megohm range. L insulation r v rated 304 8 1 where.

If during periodical testing insulation resistance of cable is found between 5 and 1 mω km at buried temperature the subject cable should be programmed for replacement.