A megohmmeter is the name of a device used for the testing of both electrical and insulation resistance, sometimes referred to simply as an IR tester. An IR test is normally carried out with a high voltage signal being sent into the object that requires testing, such as a motor or wire.
How do you use an IR tester and how do you troubleshoot the tester if you suspect it is not working as intended?
What do IR testers measure and how do they work?
It is important to grasp the measurements used by IR testers to have a complete understanding of how they actually work. The measurements produced by IR testers are able to be reduced to ohms, which are a measure of electrical resistance. The amount of electrical measurement is determined by the amount that a material is able to reduce the electrical current running through it.
These devices are known as insulation testers as they measure insulation resistance, which involves carrying out an assessment of the insulation’s integrity, which is vital to ensure equipment damage and electric shocks can be avoided. Other IR testers may also be able to read current output and voltage.
IR testers make use of a low-current, high-voltage DC charge for the purpose of measuring resistance within motor windings and wires in order to identify insulation that is damaged or faulty and current leakage.
Using an IR tester
IR testers generate voltage in order to work out the high resistance value of insulation. To perform an IR test consult the manual of your particular model and follow these steps.
1. Cut the power
It is important to be certain that you have eliminated any voltage that could be running through the wires that are to be tested.
2. Uninstall the wires
The wires to be tested should be disconnected from the circuit at both ends as well as from all of the feeding wires within motors.
3. The ground wire should be connected
One of the leads of the IR tester should be connected to a ground connection such as the electrical frame, wire insulation or ground.
4. Connecting to the conductor
The other IR tester lead should be connected to the conductor, for example the exposed copper of the motor terminal or wire.
5. Building the voltage
The generator handle should be cranked to build voltage, which will take between two to five seconds.
6. Reading the meter
The next step is to read meter, with the tested object determining the safe reading. Readings should equal one megohm for every 1000 volts of operating voltage.
7. Completing testing
The testing of the remaining terminals or wires should then be completed.
Troubleshooting
It is important to know whether or not an IR tester is functioning correctly. To work out the IR value, the voltage should be applied and the steady-state leakage current measured, then divided by the current. If the insulation resistance does not meet and is less than the required value, then the test has failed and there may be an issue with your IR tester.
To make sure your IR tester is functioning as intended, it should be calibrated every year to ensure the accuracy of its readings.
