Insulation resistance test- 9 safety tips to follow.
Safety is a sense. No instrument or tools can guarantee safety. Only safe practice and quality tools can ensure the safety. When you are to do insulation resistance test there is risk of both human injury also the probable damage to the machine itself. So you should follow the safety tips while doing an insulation resistance test.
Safe procedure of insulation resistance test
1. Work on de-energized circuits whenever possible. Use proper lock-out/tag-out procedures. If these procedures are not in place or not enforced, assume the circuit is live.
2. Use protective gear. Use insulated tools, Wear flame resistant clothing, safety glasses, and insulation gloves, Remove watches or other jewelry, Stand on an insulation mat.
3. Never connect the insulation tester to energized conductors or energized equipment and always follow the manufacturer’s recommendations.
4. Shut down the equipment to be tested by opening fuses, switches, and circuit breakers.
5. Disconnect the branch circuit conductors, grounded conductors, grounding conductors, and all other equipment from the unit under test.
6. Discharge conductor capacitance, both before and after the test. Some instruments may have automatic discharge functions.
7. Check for any leakage current through fuses, switches, and breakers on de-energized circuits. Leakage current can cause inconsistent and incorrect readings.
8. Don’t use an insulation tester in a dangerous or explosive atmosphere since the instrument can generate arcing in damaged insulation.
9. Use insulated rubber gloves when connecting the test leads.
Insulation resistance test procedure
Before performing an insulation resistance (IR) test- 6 important cautions to follow.
The IR or Insulation Resistance test to check the insulation integrity of electrical system and equipments. To achieve a perfect IR result care and precautions should be taken in to practice.
The accurate IR test result is important as on the basis of this IR test, you are to take decision whether an equipment is to discard or to continue.
· The system or equipment is taken out of service and disconnected from all other circuits, switches, capacitors, brushes, lightning arrester, and circuit breakers.
Make sure that the measurements are not affected by leakage current through switches and over current protective devices.
Plus as you are injecting high voltage Direct current for IR test, equipments are not meant for DC might be damaged with IR test.
· The temperature of the conductor is above the dew point of the ambient air. When this is not the case, a moisture coating will form on the in-sulation surface, and, in some cases will be absorbed by the material.
· The surface of the conductor is free of carbon and other foreign matter that can become conductive in humid conditions.
· Applied voltage is not too high. When testing low voltage systems; too much voltage can overstress or damage insulation. The recommendation from the manufacturer must be followed.
· Make sure that the system under test has been completely discharged to the ground. The grounding discharge time should be about five times the testing charge time.
This is very important, if you do an IR test on a system, make sure to discharge it properly for a considerable time.
· The effect of temperature is considered. Since insulation resistance is inversely proportional to insulation temperature (resistance goes down as temperature goes up), the recorded readings are altered by changes in the temperature of the insulating material.
It is recommended that tests be performed at a standard conductor temperature of 0 °C (68 °F). As a rule of thumb, when comparing readings to 0 °C base temperature, double the resistance for every 10 °C (18 °F) above 0 °C or halve the resistance for every 10 °C below 0 °C in temperature.
For example, a one-megohm resistance at 40 °C (104 °F) will translate to four-megohm resistance at 0 °C (68 °F).
precautions before doing an IR test