the Navy. The megger (fig. 7-25) is capable of several test voltages up to 1,000 volts, depending on the setting of the selector switch. Ohmmeters are generally designed to include batteries as voltage sources. These batteries apply approximately 1/2 to 9 volts to the circuit under test.
The design of the megger is such that the needle floats freely until the generator is operated. When the generator is not operating, the needle may come to rest at any point on the scale. This characteristic is due to internal design, unlike that used in the typical ohmmeter.
Figure 7-26. - Typical megger test instrument hooked up to measure insulation resistance.
Figure 7-25. - Typical megohmmeter tester.
The megger is used to measure high-insulation resistance. The high resistance may be between windings of a transformer or motor or between the conductor in a cable and the conduit or sheath surrounding the cable (fig. 7-26).
If the test leads connected to the line and earth terminals are open-circuited (as when they are not allowed to touch anything) and the hand-cranked
Figure 7-27. - Typical indicating scale on the megger insulation tester.Continue Reading