How To Perform An Insulation Resistance Test


Every electrical wire in your office, whether it is a cable or connected to a switch or any high-voltage equipment’s like motors or generators, is covered with some form of electrical insulation to ensure safety. But, is your insulation effective enough? Have you noticed some of your power is lost along the way for some reason?

It is a known fact that excessive heat, cold, moisture, vibration, dirt, oil, and corrosive vapours can lead to loss of insulation and leakage. However, regular insulation resistance tests with IR testers, like those at RS Components, are key to detecting any imminent insulation failures and prevent accidents, electrical hazards and other losses due to poor insulation. You would also need to perform IR testing during the initial installation to ensure that the legal specifications are met. 

But, how do you perform an IR test in your office? How do you know whether the IR values you had measured are satisfactory for your equipment? 

For your convenience, we have compiled the various phases done to perform a successful insulation resistance test below.

Insulation Resistance Test

The measurement procedure varies according to the type of connection. The IR test procedure has four phases namely charge, dwell, measure, and discharge. 

First phase – Charge

In the first phase, you should increase the voltage from zero to the preferred voltage of your equipment, so that it provides the stabilization time and limits the inrush current to the DUT.

Second phase – Dwell

When the voltage reaches the required value, you should allow it to dwell/hold for a period of one minute. Take note that the one-minute interval is a standard industry practice.

Third phase – Measure

Once the voltage is allowed to dwell/hold, you can take the measurement of the insulation resistance value. 

Fourth phase – Discharge

After measuring the voltage for a selected time, the DUT is discharged back to 0V for the final phase of the test.

IR testers usually have 4 output connections – ground, shield, (+), and (-). This covers a wide range of applications. The output voltage is usually in the range of 50 to 1000 Volts DC. 

IR values

Once the test results are measured, it is necessary to compare the current IR values with your previous IR readings. Also, remember to use the same IR tester while comparing previous measurements.

A high level of resistance indicates that the insulation is working properly as it is allowing very little current to escape. On the other hand, a low level of resistance means that a significant amount of current may be leaking through and along with the insulation. Any values below the standard or sudden deviations from your previous values should be noted and inspected. It is important to note that there are no standard IR values; the acceptable IR values will vary from equipment to equipment.

Insulation testers offer noise-free, reliable results and are perfectly safe and easy to use, making them the ideal solution for all troubleshooting, commissioning, and preventative maintenance application.