Electrical insulation starts to age from day one and over time its insulating properties deteriorate. Certain factors can accelerate deterioration, such as temperature extremes and chemical exposure. And this can be very damaging to equipment, electrical circuits and most importantly, the safety of the building. As such, it’s important to identify and degradation of the insulation as soon as possible in order to take the appropriate steps to eliminate the risk.
The best way to check the state of the insulation is to measure its resistance. If there’s high resistance, the insulation is good, and if there’s low resistance, the insulation is poor. The resistance can be measured using a tool called insulation resistance tester. Since this tool has such an important role, it’s crucial to choose the right one for the job.
The Type of Equipment
Different resistance testers are used for different equipment. So, take note of all the equipment you plan to inspect. Write down each equipment’s nominal voltage rating which you can find on the nameplate. Also, consider the number of tests you will be performing over the timespan of a year. Depending on the nominal voltage, you will determine whether you need a 1KV or a 5KV insulation resistance tester. In most cases, a 5KV is the best choice as it allows to inspect lower voltage equipment like 500V, 1KV. or 2.5KV. Whereas the number of tests in a year will help you decide whether to invest in extra features for convenience as well as consider the durability of the instrument.
The Voltage Requirements
While the nominal voltage is clearly stated, often manufacturers do not provide information about the test voltage needed for DC insulation resistance. When that happens, the only solution is to use the practice data from the industry. For that reason, the International Electrical Testing Association has provided a list of recommendations for electrical systems. According to these recommendations, equipment that has a nominal voltage of 250 volts will need a minimum insulation resistance test voltage of 500 volts. For larger nominal voltages like 15 000 volts or more, you’ll need a minimal test resistance voltage of 2 500. So, pay attention to the numbers.
The Category Rating
Insulation resistance testers are rated from category 1 to category 4. Category 1 testers can be used to measure voltages from a secondary circuit that has been specially protected. With that being said, category 1 testers are usually applied to electronics, circuits powered by low voltages, special equipment and similar gear. Category 2 are for wall outlets and plug loads. Category 3 are hard-wired equipment like circuit breakers and similar systems. Category 4 are devices made for utility measurements.