5 reasons to run an IR test

7 July 2021


Insulation is everywhere! Every electric wire in your substation, plant, or PV system—whether it’s in a motor, inverter, transformer, or switchgear—is covered in electrical insulation. We could keep listing things with electrical insulation, but that would get old fast. What we will tell you is that insulation is there to keep the electrical current right where it is supposed to be—in its path along the wire conductor. Which brings us to a great question…

What is insulation resistance?

Ohm’s law tells us that the more voltage we have, the more current there will be. And the lower the resistance of the wire, the more current you’ll get at the same voltage. Remember: Voltage = Current X Resistance, right? Right.

Insulation resistance (IR) is a measurement of how good or bad your insulation is, which can help give you an overall assessment of your electrical equipment’s health. By the way, no insulation is perfect—with infinite resistance—but good insulation has a relatively high resistance to current. Likewise, poor insulation is going to have a relatively low resistance value.

Download guide to insulation resistance testing 

What is an IR test?

To measure it, you’re going to have to run an IR test. In case you missed it or you’re new here, IR is short for insulation resistance, not infrared. Don’t make that mistake; you’ve been warned.

Anyways, the actual values of resistance can vary greatly depending on environmental factors like temperature and moisture content. So, keeping good records is of the upmost importance. With a little record keeping and a regular testing schedule, you can get a really good picture of your equipment’s electrical health.

To run an IR test, you’ll need an insulation tester. Traditionally, they were hand-cranked, but the more modern testers are battery or line-operated. Some people are still rockin’ their classic hand-cranks though, so to each their own! If you are on the market for an upgrade, check out the MTR105. It’s way more than an insulation tester; it really does it all.

Since 1889, when Sydney Evershed and Ernest Vignoles—our founders—invented the very first one, the insulation tester has modernized quite a bit, but the mechanics of the test haven’t changed. Insulation testers apply a DC voltage across insulation, which triggers a small leakage current—or resistive current—through it. Your tester will then calculate the resistance with Ohm’s law and shoot out a measurement on the screen. Lucky for you, there’s no math involved!

Why should you measure insulation resistance?

There are probably hundreds of reasons why you should be measuring insulation resistance, but here’s our top 5.

Extend the life of your equipment

When insulation is well maintained—with periodic testing and good record keeping—it’s easy to identify persistent downwards trends in insulation resistance. These are going to indicate that there’s trouble ahead. The good news is that you’re usually given plenty of warning time to plan preventative maintenance accordingly.

Without routine testing, it’s impossible to predict impending failures and proactively support your equipment’s health.

Save money

Likewise, when equipment fails unexpectedly, it’s a mess. For example, taking a motor offline—with unplanned downtime—could result in major production or financial losses for your plant. Not to mention, the cost to completely replace equipment after a failure is way more expensive than simply making specific repairs to the insulation. With regular IR testing, this is exactly what we’re trying to prevent.

It’s quick and easy

There isn’t a recommended time for running an insulation test because of the huge range of equipment that might be under test, but typically tests run for 30 seconds or 1 minute.

It’s also much simpler to run a test than you may think. Once the test leads are in place, just turn the selector switch to the desired voltage or function and hit test. Depending on the model you are using, you may need to hold down the button for the duration of the test or just a few seconds. Before you start testing, make sure to consult your manufacturer’s user guide for further instruction.

Don’t just take our word for it. Check out one of our IR testers in action below. Feel free to pull out a stopwatch too if you’re feeling extra suspicious.

You can’t damage anything

If you’re worried about damaging your equipment, stop. A hipot tester will do that, but an insulation tester isn’t going to take any life off of your test item. Even though the voltage is considerably high, the output current is limited to only a few milli-amps, so it lacks the power to cause any damage.

There’s a tester for everyone

Our insulation testers aren’t really application specific, they can all get the job done! Some of them are geared more towards specific industries, based on the built-in features, but that doesn’t mean other technicians or contractors can’t use them! If you’re choosing a tester, it’s up to you to decide which features and specifications are most important for your day-to-day job functions, as well as your personal preferences.

There’s truly a tester that fits every budget, measurement range, and voltage requirement. With so many options, it can be overwhelming at first. Once you decide what’s most important to you, picking an insulation tester gets easier.

To learn more about why you should run IR tests, click here to download our complete guide to electrical insulation testing.

Click here to see our IR testers