BM5200 5 kV insulation resistance tester

This battery-powered tester comes with a digital and an analogue arc display

Designed for high voltage insulation resistance testing of cables, rotating plant machinery, transformers, switchgear, and industrial applications

Three insulation resistance (IR) test modes

CAT III 600 V rated with additional safety features

Guard terminal for accurate results

Perform DC insulation tests

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About the product

The BM5200 5 kV insulation resistance tester has been designed for high voltage insulation resistance testing in the maintenance and servicing of cables, rotating plant machinery, transformers, switchgear, and industrial applications.

With the BM5200, you can perform DC insulation tests at 250 V, 500 V, 1000 V, 2500 V, and 5000 V. Its insulation resistance measuring range is from 100 k Ω to 1000 G Ω. What’s more, it provides an automatic discharge for capacitive circuits under test and displays decaying voltage.

The instrument is not only battery powered, but it also comes with both a digital and an analogue arc display. It also uses a guard terminal to increase the accuracy of its results by minimising the effects of surface leakage that can lead to measurement errors.

Troubleshooting

Why does a fuse symbol appear at the top of my display?

This symbol indicates that the instrument has experienced an overcurrent causing the fuse to blow. The fuse is in the battery compartment; you can replace it with the spare fuse.

The voltage output is zero on all ranges

A broken standoff between the display and control board will cause zero voltage output on all ranges. Such a break is usually caused by rough handling. You will need to send the instrument for repair in such a case.

Interpreting test results

Insulation resistance readings should be considered relative. They can be quite different for one motor or machine tested three days in a row, yet it does not mean bad insulation. What matters is the trend in readings over a longer period, showing lessening resistance and warning of coming problems. Periodic testing is, therefore, your best approach to preventive maintenance of electrical equipment, using record cards or software to trend the results over time.

Whether you test monthly, twice a year, or annually depends upon the equipment's type, location, and importance. For example, a small pump motor or a short control cable may be vital to a process in your plant. Experience is the best teacher in setting up the scheduled periods for your equipment.

We recommend making these periodic tests in the same way each time. That is, with the same test connections and test voltage applied for the same length of time. Additionally, we recommend performing tests at about the same temperature or correcting them to the same reference temperature. A record of the relative humidity near the equipment during the test is also helpful in evaluating the reading and trend.

Periodic insulation resistance tests

In summary, here are some general observations about how you can interpret periodic insulation resistance tests and what you should do with the result:

Condition	What to do
Fair to high values and well maintained	No cause for concern
Fair to high values but showing a constant tendency towards lower values	Locate and remedy the cause and check the downward trend
Low but well-maintained values	Condition is probably acceptable, but you should investigate the cause of low values
So low as to be unsafe	Clean, dry out, or otherwise recondition the insulation to acceptable values before placing equipment back in service (test wet equipment after drying out)
Fair or high values, previously well-maintained but showing a sudden decrease	Make tests at frequent intervals until you locate and remedy the cause of low values; or until the values have become steady at a lower level but safe for operation

Temperature dependency

The resistance of insulating materials decreases markedly with an increase in temperature. However, we’ve seen that tests by the time-resistance and step-voltage methods are relatively independent of temperature effects, giving relative values.

To make reliable comparisons between readings, you should correct the measurements to a base temperature, such as 20 °C, or take all your readings at approximately the same temperature.

A good rule of thumb is: For every 10 °C increase in temperature, halve the resistance; or, for every 10 °C decrease, double the resistance.

Each type of insulating material will have a distinct degree of resistance change with temperature. Factors have been developed, however, to simplify the correction of resistance values. Please refer to the document linked below to find such factors for rotating equipment, transformers, and cable (Section: Effect of Temperature on Insulation Resistance).