Insulation Resistance Testing – The Complete Guide

What is the Insulation Resistance Test? 

An insulation resistance test or IR test is used to calculate the overall resistance between two selected points isolated by the electrical insulation. The purpose of the test is to check the effectiveness of the electrical insulation in stopping the flow of current. The insulation resistance tests are used to measure the quality of insulation in two ways. First during the manufacturing of the products and also during the use of the product at any time.

Such tests play a crucial role in the advance detection of the expected insulation damages. This proves very helpful in avoiding the frequent mishaps and costly repair works related to electrical products. An IR tester is used to measure the insulation resistance. We will discuss these testers later.

The insulation testing setup for grounded and ungrounded components varies greatly. To test ungrounded appliances, a 2 wire ungrounded connection setup is used. This type of device includes capacitors and resistors. See the pic below to understand it.

Setup for ungrounded components to check insulation resistance

Fig 1: Setup for ungrounded components to check insulation resistance. Here GRD stands for DUT Guard Source (Source of pic: https://www.chromausa.com/)

On the other hand, for the grounded appliances 2-wire grounded measurement is mostly used. In a grounded part, one of its two connections is attached to the ground. While in the ungrounded component none of the connection is attached to the ground. An example of a 2-wire grounded connection is the calculation of insulation resistance of cable submerged underwater. See Figure 2 to see such connections.

Wire grounded connection

Fig 2: 2-Wire grounded connection (Source of pic: https://www.chromausa.com/)

How is Insulation Resistance Measured?

Measurement of Insulation resistance or IR test consists of four steps. These steps are charge, dwell, measure/calculation, and discharging. 

In the first step i.e. the charging step, the voltage is increased to the required level from zero. This helps in giving the needed stabilizing time and slows down the input current intake to the DUT. After achieving the selected voltage, the voltage is allowed to decrease or maintain at the selected level. This is the second step and called the dwell.

 At this moment, the measurements of the insulation resistance are taken. This is the third step called the measurement step. In the fourth and final step, the DUR voltage is dropped back to zero after taking the measurements. 

Insulation resistance IR tester normally has up to four output connections. Their names are ground, shield, +, and -. These four connections are used for different types of applications. Here it is important to note that the output voltage usually ranges from 50 to up to 1000 V DC. In perfect resistance value should be higher in the range of 35 to 100

Check figures 1 and 2 to see how the DUT connections are attached. The IR tester measures the resistance and displays it. To measure the insulation resistance, the megger test performed by the megger tester is most popular, followed by the fluke 1507 insulation tester. 

Important of Insulation Testing?

As we all know the color coating that surrounds a wire that protects the wire and people. However, this insulation is not forever and it starts to deteriorate over time. With deterioration, the quality of insulation also starts to decrease. If the wire is being used in a harsh climate or in certain industries, the rate of wire deterioration is also high. Therefore, it is important to check the state of insulation frequently for the safety of workers. 

The insulation tests are performed to make sure the insulation resistance is in the acceptable range. There are quite a few tests currently under use to check any insulation breakage. However, the best of all and easiest to is the insulation resistance test also known as the IR test. There are certain purposes and advantages of using the IR test. Let’s have a look at a few of them.

  • The IR test is used to make sure the insulation requirements are met and also to verify the right hookup.
  • This test is important as a regular incident preventive maintenance job.
  • The test is also important for maintaining quality control during the production of electrical appliances.
  • It is also helpful for troubleshooting purposes.

Types of Insulation Resistance Tests

Generally, three types of insulation resistance tests are in use. These types include Short-time/spot reading test, Time-resistance method, and Dielectric absorption ratio. All these tests are performed using the Megger insulation tester. 

Short-Time Test

This method is also known as a short time or spot reading test. In this method, you just need to connect the meter megger with the wire insulation you want to test. As the name depicts, you operate the system for a very short period of time usually less than a minute. See figure 3 to see how the resistance generally varies with time.

How normal insulation resistance curve looks along the time for the spot reading test

Figure 3: This is how the normal insulation resistance curve looks along the time for the spot reading test. The resistance is measured in Megohms (Source of pic: http://www.techni-tool.com/)

To check the resistance across the insulation, just pick a point on the curve of continuous increasing resistance value as seen in figure 3. Generally, the value is lower in the case of only 30 seconds, while the value is higher when the value is taken for 60 seconds. Remember the value of resistance may change with change in temperature and humidity.

Time-Resistance Method

This method has a distinct advantage over the short-time test as its value doesn’t get affected by the temperature. It also provides the right information without taking help from past tests. Its values depend on the absorption effect of the right type of insulation when compared with the insulation containing the moisture or contamination. 

In the time resistance method, you need to take multiple readings at a particular time and compare them with each other. This kind of insulation testing is referred to as absorption tests. In the case of the appropriate insulation, resistance will increase continuously over the selected period of time. 

On the other hand, if the insulation is contaminated and has moisture, the resistance value should be low. This means the insulation is tempered and needs repairing. See figure 4 to see the results of appropriate and contaminated/moisture ridden insulation.

Trends of different insulations in Time-Resistance Method

Fig 4: Trends of different insulations in Time-Resistance Method (Source of pic: http://www.techni-tool.com/)

Dielectric Absorption Ratio

This test shows that good insulation demonstrates a slow increase in IR when the test voltage is applied to it. After connecting the connection appropriately, the test voltage is applied and the values of IR are noted at two separate times. This time is usually 30 seconds and 1 minute. However, it can be 60 seconds and 10 minutes depending on the electrical appliances. 

In order to calculate the value of IR, the 2nd value is divided by the 1st value. For example, the value of resistance at 10 minutes is divided by 1 minute to calculate the value. This ratio is known as the polarization index (PI). We find the state of insulation resistance with the help of PI. See the table below in this regard.

Insulation condition with regard to PI

Table 1: Insulation condition with regard to PI. The higher the PI value, the better is the condition of the insulation. (source: https://www.ecmweb.com)

Insulation Resistance Testers

Without a quality IR tester, the true value of insulation resistance can never be found. Here, it is important to note that a particular IR tester can’t be good for all types of industries and applications. There are certain factors that determine which type of resistance testers should be used. Some of these factors include:

  • What type of equipment is being tested?
  • The place and industry type where the IR tester needs to be used.
  • The magnitude of the voltage required for the testing.
  • Other factors include the experience of the person conducting the tests and the standard of safety at the place where tests will be conducted.

Best IR Testers

There are dozens of IR testers in the market. Every tester has some pros and cons. However, some of the testers are better than the others. Let’s have a look at some of these testers.

Megger Megohm Meter- Victor VC60B+

Victor VC60B+ insulation tester megger is among the best available IR testers in the market. This tester provides accurate results and comes with a 9V powerful battery. Using this, one can test resistance at various voltages including 250, 500, and 1000V. The best part of this tester is the great range of testing including as low as 0.1 to as high as 2000 Megaohm. 

The Megger Megohm Meter.

Figure 5: The Megger Megohm Meter. (Source of Pic: Amazon.com)

Victor VC60B+ insulation tester can operate at a wide range of temperature and humidity. The meter megger comes with a wide, easy to use and understand LCD display screen. The insulation tester megger is best to use in telecom, mechanical and electrical wires, and appliances.

Digital Megohmmeter Insulation Tester- Fluke 1507 Insulation Tester

The next IR tester on the list is Fluke 1507 insulation tester. The is a lightweight, easy to handle tester. It works on AA Alkaline batteries and is literally a noiseless tester. Like the megger meter, it can test resistance at various voltages including 50, 100, 500, and 1000V. It comes with a great insulation testing range, starting from as low as 0.1 Megaohms to as high as 10 Gigaohms. 

A Fluke 1507 Insulation Tester

Figure 6: A Fluke 1507 Insulation Tester (Source of Pic: Amazon.com)

The best thing about Fluke 1507 insulation tester is its automatic calculations of PI and dielectric absorption ratio. It also powers off automatically when not under use for a long time. It is best for the professional and technologically advanced industries. 

R5600 Insulation Tester

Designed by the REED, the R5600 insulation tester comes with strong and double molded plastic which makes it very durable. You can test resistance at various voltage levels including 250, 500, and 1000V. It can measure resistance up to 2000 megaohms. It is equipped with a conventional dual display screen. This makes its measurement easy to understand and read. 

R5600 insulation tester is best for indoor testing of electrical appliances, motors, and wires.

 A R5600 Insulation Tester

Figure 7: A R5600 Insulation Tester (Source of Pic: Amazon.com)

Safety Precautions for Insulation Resistance (IR) Testing

During insulation resistance testing, it is necessary to take some precautionary steps to ensure the safety of the workers. Let’s have a look at some of the important safety precautions given below.

  • Never perform insulation tests on energized electrical appliance or wire. Always perform the test when it is turned off. 
  • Keep away from holding or touching the test meter as much as you can. 
  • Close down equipment and disconnect all the connected switches. Discharge the terminals only into the earth.
  • In order to see if the circuit is dead, use the three points testing method. These points are: check and test the available live circuit, after it tests the selected circuit, and test again the first live circuit to see if the IR meter is working well. 
  • Protective equipment is necessary if you are testing the live circuit. Protective equipment is also necessary if you working in a possible inflammable environment.
  • Use insulated gloves while testing and connecting the switches and leads for tests.

The Final Words

Insulation resistance testing is important to check the condition of insulation over a wire or electrical appliances. It also plays important role in incident prevention related to electricity and checking quality control during the production of electrical appliances. There are three types of IR tests including the Short-Time Test, Time-Resistance Method, and Dielectric Absorption Ratio. These methods are used for separate applications.

The quality and reliability of the IR tester are very important to make sure the IR measurements are 100% reliable. To select an appropriate IR tester, keep important factors in mind. Some of these factors include what type of equipment is being tested, place and industry type, and voltage requirements for the IR testing. Last but not the least, always follow the above-given precautions before performing the IR testing.

Facebook Valuation Now Higher Than eBay’s

Facebook has technically overtaken eBay to become the third largest technology company in the United States. The company’s shares are now trading at $16 on SecondMarket – an exchange for shares of privately held companies. At this price, the valuation of the company stands at $41 billion that is a tad more than the $39.3 […]

Facebook has technically overtaken eBay to become the third largest technology company in the United States. The company’s shares are now trading at $16 on SecondMarket – an exchange for shares of privately held companies. At this price, the valuation of the company stands at $41 billion that is a tad more than the $39.3 billion valuation that eBay holds at the NASDAQ stock market. Only Amazon – at $74.4 billion valuation and Google – with $192.9 billion value are above Facebook.

The revelation comes on the heels of speculation that Facebook is announcing a new email product to take on the likes of Gmail and Hotmail. An announcement in this regard is expected later today. The news is also likely to give a major impetus to anticipation about the social network’s IPO plans. Will Facebook open to the stock markets next year?

Microsoft XBox 360 Sale Numbers For September Announced

Microsoft appears to be doing really well in the gaming console segment. The company has reported that over 484,000 units of their XBox console was sold during the month of September 2010. That makes Microsoft the number 1 player in the segment for the fourth month in a row. The sale numbers are also up […]

Microsoft appears to be doing really well in the gaming console segment. The company has reported that over 484,000 units of their XBox console was sold during the month of September 2010. That makes Microsoft the number 1 player in the segment for the fourth month in a row. The sale numbers are also up 37% compared to XBox 360 sales in September last year. The company has also announced that the sale of games have seen a terrific rise thanks to the launch of the new Halo : Reach. Microsoft apparently sold 3.3 million units of the game during the month of September.

The numbers are interesting on two counts. Firstly, Microsoft will be entering the holiday shopping season on the back of this impressive sale numbers over the past four months. Gaming consoles are one of the very hot selling commodities during this season and Microsoft should expect to do well. Secondly, the impressive sale numbers should also help the company in the sale of Windows Phone 7 handsets considering that the mobile platform is tightly integrated to XBox Live. Existing users should surely contemplate buying a Windows Phone 7 device.

Microsoft (NASDAQ:MSFT) shares rose 1.23% in the market yesterday and are currently trading at $25.57 in the after-hours.

iPhone 4 Cases Causing Rear Glass Pane To Crack?

Apple may have been selling their new iPhone 4 like hotcakes. But there is no denying the fact that the launch has brought about several challenges to Apple engineers. The death grip and proximity sensor issues definitely take the lead, but there are several other challenges too that have surfaced time and again. It seems […]

Apple may have been selling their new iPhone 4 like hotcakes. But there is no denying the fact that the launch has brought about several challenges to Apple engineers. The death grip and proximity sensor issues definitely take the lead, but there are several other challenges too that have surfaced time and again.

It seems that these issues fail to die down. We are now hearing that a new issue is brewing up at Cupertino over the possibility of the rear glass pane of the iPhone 4 to crack due to third party cases licensed by Apple. The issue is not exactly with the free bumpers that Apple offered to their iPhone 4 customers, but with other slide-on cases that are popular among iPhone users. Gdgt writes,

“Apple has apparently found that non-bumper style cases — specifically those that slide onto the iPhone 4, which are occasionally prone to particulate matter getting caught between the rear of the phone and the case — can cause unexpected scratching that could quickly develop into full-on cracking or even much larger fracturing of the entire rear pane of glass. To put it another way: Apple is afraid you might buy a standard slide-on iPhone case, put it on your phone, and then discover the next time you take it off that the entire back of your device has been shattered by no fault of your own.”

The report notes that though this issue is yet to see any widespread prevalence, Apple is already working to ensure this issue does not affect future products. That could mean that the next generation iPhone may not be having a glass back.

Updated Paypal iPhone App Allows Electronic Deposit Of Checks

eBay-owned Paypal has been bringing a number of innovative technologies to the iPhone. After letting users to ‘bump’ their phones in order to exchange contacts and send money with their earlier update, Paypal has now announced yet another update to their iPhone app that will make it easier for users to deposit money into their […]

eBay-owned Paypal has been bringing a number of innovative technologies to the iPhone. After letting users to ‘bump’ their phones in order to exchange contacts and send money with their earlier update, Paypal has now announced yet another update to their iPhone app that will make it easier for users to deposit money into their account.

The new electronic check deposit feature will allow users to simply capture a picture of the front and back sides of their checks and submit it electronically for the money to be automatically transferred from the bank to their Paypal accounts.

While this is definitely a convenient way to transfer money, not all users are happy. A review of the new feature on the App Store brings up a very pertinent point,

“PayPal proudly announced the new check deposit feature last week to much fanfare, claiming this version would be released in a day or so. Well, try several days. It’s immediately slower, but it’s worth it, right? After all, we’ve suffered for years with PayPal pretending we have to wait three business days for ACH transfers to happen, so at least now we’ll have a way to deposit funds instantly. Oh, think again! Now they want us to believe that instead of same-business day crediting that’s a normal part of Check 21, we’re supposed to wait six business days “or longer” for the deposit. Yes, seriously. Whatever you do, don’t use this feature; you’d be better off mailing your check to a bank in another state! PayPal stands to make a fortune off the float on these check deposits. Unreal!”

You can still check out the new version of the app by clicking here.

Now Buy iPad Online At Amazon

It has been over six months since the iPad first launched in the US market and it is only natural that the sale numbers are now seeing a dip. Quite expectedly then, Apple has been opening up the sale channels in order to maximize the sale of the tablet computers. Soon after Target announced that […]

It has been over six months since the iPad first launched in the US market and it is only natural that the sale numbers are now seeing a dip. Quite expectedly then, Apple has been opening up the sale channels in order to maximize the sale of the tablet computers. Soon after Target announced that the new iPad shall be available on their retail stores from earlier this month, Amazon too has announced that their online store will now start selling the tablet computer.

At present, the 3G enabled versions are not on stock. That leaves the choice between the Wi-Fi versions of the 32GB and 64GB iPad models only. You can check them out now on Amazon by clicking here. Do check them out since the price is the same as the official retail price.

AirPrint Support For iPod Touch 2G Dropped

It has been over two weeks since Apple officially introduced us to their new iOS-based wireless printing technology caleld AirPrint. Back then, the new feature was reported to be supported on iPod Touch 2G and later and iPhone 3GS and later. Bizarrely though, the press release and the AirPrint page on Apple have been silently […]

It has been over two weeks since Apple officially introduced us to their new iOS-based wireless printing technology caleld AirPrint. Back then, the new feature was reported to be supported on iPod Touch 2G and later and iPhone 3GS and later. Bizarrely though, the press release and the AirPrint page on Apple have been silently modified since then to note that the feature is actually supported on iPod Touch 3G and later (and not 2G as was initially proclaimed).

It is not clear whether Apple has merely corrected a typo that existed earlier in their press releases or if this is a technical/business decision to not allow this new technology on the older iPod Touch model.

Nevertheless, this is not an entirely surprising decision. The second generation model of iPod Touch is pretty close in technology to the iPhone 3G unit and considering that AirPrint is not supported on iPhone 3G, it is pretty reasonable to expect Apple to pull the strings this way.

HDR Photography On iPhone 3GS May Come In Future Update

Apple is always known to intentionally block features on older devices in order to push people to graduate to newer devices. One such functionality that is available on iPhone 4 but is not provided on the older iPhones is the HDR capability. As you may already know, this functionality delivers effective contrasts on pictures by […]

Apple is always known to intentionally block features on older devices in order to push people to graduate to newer devices. One such functionality that is available on iPhone 4 but is not provided on the older iPhones is the HDR capability. As you may already know, this functionality delivers effective contrasts on pictures by superimposing three pictures that are taken in normal, under-exposed and over-exposed modes.

Now, there are jailbreak apps that will let you enable this functionality on the older iPhones. From what we’ve heard in the past, the functionality works perfectly on the older models and there is no reason why Apple shouldn’t have offered the feature to the older iPhones as well. Nevertheless, if ever Apple had decided to block this feature on older models, it appears that this could have been a last-minute decision. Folks at 9to5Mac have uncovered a couple of HDR icons from the iPhone SDK that reference to iPhones with retina display and those that do not have this display. The difference can be noted in the nomenclature that usually contain a @2x in case of documents pertaining to the  retina display.

HDR on iPhone 3GS

If you were to stay an optimist, what this could mean is that Apple could bring the HDR functionality to the older iPhone; iPhone 3GS primarily, via a future software update. The question is however whether Apple would want to.

Second iOS 4.2 Beta Version Available For Download

You must be already aware that the next version of iOS – version 4.2 is scheduled to become available for public consumption in November of this year. As we move towards the official launch date, Apple has been releasing beta versions of this new mobile operating system for developers who will need it to format […]

You must be already aware that the next version of iOS – version 4.2 is scheduled to become available for public consumption in November of this year. As we move towards the official launch date, Apple has been releasing beta versions of this new mobile operating system for developers who will need it to format their applications to be compatible with the new platform.

Two weeks after the first beta release of iOS 4.2 was made, we now have the second beta of the upcoming iOS software released to the developer community. To get started, you need to log in to your Apple developer account here and find the appropriate link for download.

The upcoming version of iOS brings a number of new features like AirPlay and AirPrint to the iDevice. Besides this, the new version will also let iPad users get access to multitasking, folder management and threaded email access. The enhancements made in the latest beta release is not known as yet. Keep looking out for the same, though.

New iPad 2 Features – Camera, Mini-USB [Rumors]

The Apple iPad has only recently been seeing some worthy competition from Samsung and RIM. Both these rivals are looking at the holiday season as the perfect season to take on competition from the iPad and it is easy to think Apple too could be launching a mini-iPad that is closer in form factor and […]

The Apple iPad has only recently been seeing some worthy competition from Samsung and RIM. Both these rivals are looking at the holiday season as the perfect season to take on competition from the iPad and it is easy to think Apple too could be launching a mini-iPad that is closer in form factor and size to these tablet rivals.

However, according to recent reports on the AppleInsider, Apple may not be launching a smaller iPad anytime soon. Instead, the company is reported to be working on a second generation 9.7″ display iPad that could come with additional features like a camera and a mini-USB.

“The analysts also said their checks found that “the 7” iPad project has not yet been finalized” and therefore said its “unlikely to be launched ahead of the new 9.7” iPad”. According to the pair, the new 9.7-inch iPad “is targeted to be thinner and lighter, with an embedded camera and mini USB.” It “could be launched in early” second quarter of 2011, they said.”

Apple has been rigorously working on popularizing its new FaceTime video calling service and so a camera was always expected. Also, considering that the iPad is a media consumption device, it makes sense to get the device lighter. Nevertheless, by not launching a unit for Christmas, Apple could not only be missing an attractive business opportunity, but could also be giving competition a free reign for the holiday season. What do you think?