Megger vs Hi pot testers

"Megger" is a trade name, they manufacture test instruments, notably insulation measuring instruments with various selected output voltages for whatever job you need them for.

When people say megger, they mean 'to measure the insulation resistance' unless they mean 'megger', which is all the above.

The Hi-Pot is high potential, normally in the kilovolt range, funnily enough some of these instruments are manufactured by "Megger".

'Meggered' means still holding the probes while you've pressed the test button... It's a wake up call to let go the button!

I can direct you to two definitions provided by Globalspec.

The first definition is for a Hipot Tester and the second definition is for a Megohmmeter. I am not sure if by megger you mean Megohmmeter but perhaps these will help you determine what you need.

"Meggers" are used to check the safety of the units insulation only. Usually the value must be well over 1 Meg Ohm as it falls (usually) in use over a long period......the name comes from the company that as far as I am aware, produced the original devices many, many years ago. Just like Biro or Hoover.....

Hi Pot (High Potential) are testers to make sure that an electronic device works even when subjected to very high voltage (I forget but it was around 6000 volts at one time I believe) on the frame ground, so that the microprocessor does not hang for example when such "spikes" happen.........

Insulation resistance testing or meggering is for low voltage circuits. It uses 500 or 100V dc to measure the insulation resistance. It is generally a go/no-go test because the resistance is so high. Some specifications call for readings above 10 megohms. In reality, if you got a reading of 11 megohms (or anything below several hundred) you should be suspicious.

High potential or hi pot testing is the slow (5-10 minutes) application of either ac or dc voltage. It also measures insulation resistance and other values. The rule of thumb for the test voltage is twice the system voltage plus 2kV but you should follow the NETA standards, which vary the voltage depending on the state of the equipment (factory, installed, used). There is a lot of discussion about ac vs. dc regarding usefulness and damage to the tested equipment.

AC and DC Hi Pot stress insulation in different ways, since they are two different animals.

I generally follow the NEMA standards of an AC Hi-Pot and DC step test for Motors.

As far as breakers, I don't know if it makes much of a difference. I have used both.

Maybe someone else could add clarity to the issue

Hi-Pot is a generic term for High Potential Test. Megger is a brand which has become a generic term for a similar testing device. In different applications, "high potential" has vastly different meanings. In integrated electronics, high potential may be 150 volts, whereas in the power industry, high voltage is above 34,500 volts.

Both hi-pots and meggers can be used for testing insulation resistance. However, testing only resistance does not give a complete picture of the health of the insulation. Meggers are usually applied for 1 minute or less, for a "snapshot" of the insulation at existing ambient conditions. Motor, generator and transformer windings, as well as medium and high voltage power cables, are usually tested for insulation power factor (which has nothing to do with cosines and angles) as well. The high potential is applied for 10 minutes, with readings taken at the 1 minute and 10 minute marks. As the voltage is applied, the winding heats up, causing moisture in the insulation system to evaporate. The insulation resistance should rise over time as more moisture is driven off. The 10 minute value divided by the 1 minute value gives a ratio called insulation power factor. The higher the power factor, the better the insulation system health. If the insulation resistance does not rise, your insulation may be contaminated or cracked.

Hi-pots are also useful for locating damage in faulted underground cables, a process called "thumping". The cable is disconnected at both ends, and the hi-pot is connected between the conductor and ground. A closed spark gap is attached in parallel with the hi-pot. As the spark gap is widened, the voltage output of the hi-pot will rise further each time before the spark to ground collapses the voltage. At some point, the spark gap becomes a higher impedance path to ground than the cable fault. The sparks no longer jump the gap. The sparking now occurs at the location of the fault. Since arcs are noisy little fellows, the location can usually be found readily with a ground microphone and headset.

AC hi-pot testing is preferred when the reactive component of the insulation needs to be tested. This is usually the case in AC generators. Occasionally, large synchronous AC motors will be AC tested, particularly if they are used for VAR compensation.

Both testers are very useful, but have different strengths. A megger is a small device, usually less than 5 kg, and operated by one person. It takes only a minute or two to set up and perform your test. The cost of a megger is usually about 5% of a hi-pot. Most meggers are limited to 500 volts DC output, although I have seen electronic meggers up to 2,500 volts.

Most hi-pots start at 50,000 volts. The one we use right now is rated for 150,000 VDC. Hi-pots contain a built-in transformer to reach that output voltage (they still plug into a standard 110 or 220 VAC wall outlet). The transformer is bulky and heavy, often requiring 2 persons to transport and set up. The extreme voltages also make it unsafe for one person to operate alone.

Nice reply...I learned something here

I've used a Simpson brand meggar a few times to test insulation values of large electric motors at a rock crusher. ( Required by gov't.) I've also used a similar device but its a GROUND ROD tester.

Pounding a piece of steel in the ground doesn't necessarily make a good ground rod. There's lots more to it and testing removes doubt.

Hello,

This link has some great white papers on the subject. Not all Hi-pot testers are as large as previously stated, some are quite portable, though only 5kV or so...

http://www.hipot.com/resource/white_papers.shtml