Megger Tests

Megger Tests Points : Megger Tests, Continuity Test, Short Circuit Test, Open Circuit Test Following tests can be performed with the help of megger:
(a) Continuity Test
(b) Short Circuit Test
(c) Open Circuit Test

In addition to above tests megger can be used for polarity test and earth continuity test. These tests are performed for checking new installation and wiring. a) Continuity Test This test is performed for checking the continuity of any circuit. In this test two terminals of megger are connected across the line and neutral terminals of the supply. Loads are connected on each point and all switches are placed in OF position. Now the handle of megger is rotated, if it shows infinity reading, then there is no short circuit in the circuit.

Now put the switch in ON position and rotate the handle of the megger, if it shows zero reading, it means that continuity is present in the circuit. But in case of infinity reading, the circuit is open. b) Short Circuit Test This test is also called insulation test. In this test the insulation of the circuit is measured with megger. Megger test leads are connected to the circuit under test. All loads are put out of the circuit and all switches are put in “ON” position, the handle of the megger is rotated. The reading is noted.

insulation resistance = 50MΩ/No of out lets

For example the insulation resistance of the circuit with 10 points will be:

insulation resistance = 50MΩ/10 = 5MΩ

If the megger pointer shows the infinity reading, it shows the best insulation. When the reading is less than infinity, it shows uncertain value of insulation. While zero reading shows the short circuit condition of the circuit. c) Open Circuit Test Open circuit means the broken conductor. While performing the open circuit test of an installation, it is completely isolated from the supply, the test leads of megger are connected to the circuit under test, the handle is rotated. If megger shows the zero value or some value of resistance, it means the circuit is Correct. But the reading is infinity, it means the circuit is open.

Megger is also used to locate the open circuit in motor windings.