A Megohmeter or insulation resistance tester is a particular type of ohmmeter used to measure the electrical resistance of insulators. Insulating components, for example, cable jackets, must be tested for their insulation strength at the time of commissioning and as part of the maintenance of high voltage electrical equipment and installations.
For this purpose, megohmeters can produce a DC (direct current) voltage of between 300 and 15,000 volts. A megohmeter produces a high voltage, low current DC charge, which allows for testing resistances commonly encountered in electric motor winding or cable insulation tests. Acceptable insulator resistance values are typically 1 to 10 megohms, depending on the standards referenced.