The Megger BM25 is a compact automated 5 kV insulation tester. It can be used to conduct polarization index, step voltage, dielectric discharge diagnostic, and standard insulation tests up to 5 T?. Results and test options are displayed on a large, clear analog/digital readout for both practicality and precision. The BM25 provides an optically isolated RS-232 port for direct download of test results. This enables the user to conduct cost-effective predictive maintenance programs. The instrument displays leakage current down to <1 nA and the capacitance of the test piece up to 10 ?F. A guard terminal allows surface leakage to be removed. Standard test voltages are preset at 500 V, 1000 V, 2500 V, and 5000 V and combined with an output voltage setting that is variable in 25 V steps. The integral timer starts automatically at the beginning of a test and can be used to control test duration. The BM25 is powered by rechargeable lead-acid batteries. The built-in charger operates from 95 V to 265 V power supplies without switch selection. The instrument is supplied complete with test leads, RS-232 interface lead, and file transfer utility software. APPLICATIONS The BM25 is designed for testing the insulation of high-voltage electrical equipment.? Its wide voltage range also allows applications for low-voltage equipment. Generators, motors, transformers, cables, and switchgear all require effective maintenance. The test techniques on the BM25 provide valuable diagnostic information. Insulation suffers from gradual, steady decline as well as occasional sudden damage. The effects of dirt, grease, moisture, vibration, and chemical attack can be tracked by recording polarization index tests which are not limited by the temperature-dependence of raw insulation resistance measurements. The polarization index (PI) is a time-resistance dielectric absorption test. PI tests are also helpful when full test records have not been maintained. To find more localized insulation problems, the BM25 includes both step voltage and dielectric discharge tests. Step voltage identifies local weak spots that respond differently as electrical stress is increased. The dielectric discharge test can show a single bad layer in multilayer insulation. The key to predictive maintenance is the trending of diagnostic tests. The BM25 can be downloaded to a PC to store test results.