# meggers



## frank (Feb 6, 2007)

To keep it simple - all you need to understand is that the Megger tests insulation values ie the insulation around the current carrying cores. Where two such cores are side by side the value of insulation needs to high enough not to allow currents from one core passing to the adjacent core. A SHORT. The Megger applies a voltage potential of 250/500/1000 volts ( depends on your instrument) between the two core and tries to break down the insulation. Where insulation is weak this will show as a low value resistance or where good up to infinity.

Frank.


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## chrisb271 (Jul 6, 2007)

I was always under the impression that nearly every electrician carried an insulation resistance tester ( megger )
I know i would certainly be lost without mine.

Infact i still have the first insulation tester i ever purchased tucked away in my garage ( he says going slightly red ) a windup thing,very basic but did the job.

most old uk electricians have found out what the wind up insulation tester does the hard way ha ha,i did !

Regards

Chris


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## brian john (Mar 11, 2007)

Few electricians in America know what meggers are much less how to utilize one (though numbers are improving). In a way that has been benificial to my business, I often have calls to come megger bus, cables or switchboards, either prior to energizing, or after a fault. Saturday night 10:26 PM awaiting a call from an electrical contractor to send a guy out to megger some cables that may have faulted.


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## knothole (Mar 10, 2007)

They are good for fishing, too. :whistling2:


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## MDShunk (Jan 7, 2007)

brian john said:


> Saturday night 10:26 PM awaiting a call from an electrical contractor to send a guy out to megger some cables that may have faulted.


If you find a fault in faulty cable, who's fault is it, really? 

In these days of political correctness, aren't we supposed to quit finding faults and only look for the good? Maybe you should send the guy out with the Megger to look for the "goods" instead of the faults all the time. It would make him feel better about himself. 

(Sorry. Just popped into my head, and I had to let it out.)


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## frank (Feb 6, 2007)

I like it. Let more pop out!


Frank


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## brian john (Mar 11, 2007)

Being basically lazy I when I compose these lenghtly responses I keep them for re-posting, my aplogies to those that read these before.

There are a variety of test that can be performed with meggers, but the primary test most electricians utilize is a go no go test, connect the megger record the readings and make a determination if the readings are in an acceptable range

Busway:

Busways should be meggered piece by piece as it comes off the truck. Then piece by piece as it goes up, the assembled busway should be meggered as each piece is added and lastly the completed busway should be meggered.

Feeders:

Feeders should be meggered as soon as they are pulled and after termination.

Switchboards and MCCs:

Switchboards should be meggered as soon as they arrive on site, after installation and prior to energizing. In addition The neutral disconnect link should be removed and the downstream neutral meggered to ground, this verifies the downstream neutral is clear from shorts to ground avoiding net current issues and the resulting EMF, additionally should you lose the neutral connection to the main switchboard the downstream connections will carry the full neutral load, which can be a fire hazard.

Panels:

Panels should be meggered when they are installed and prior to energizing. The branch circuit neutrals should be isolated from the feeder neutral and meggered to verify there no branch circuit neutral shorts to ground. AVOID NET CURRENTS and EMF

Transformers:

Like all equipment it should be meggered prior to energizing. You can not megger phase to phase as this is a direct connection through the winding. Megger phase to ground on the Primary, Phase to ground on the secondary (with the neutral ground bond lifted) and primary to secondary.

Circuit Breakers:


Large frame circuit breakers should be meggered in particular after a fault when the CB has operated. Megger line to load across each phase, phase to phase line and load and phase to ground. A simple method to do these test is to open the CB, place jumpers from Line B phase to A and C phase load side then jumpers from B phase load to line side A and C. Place your megger leads on B line and B load record your readings> Now close the CB and megger to ground.


ATS Automatic Transfer Switches:

Care should be taken with ATS’s the control panel must be disconnected to avoid damaging the control panel.

Motor: 

Motors should be meggered prior to energizing, remember that phase to phase SHOULD read a dead short you only need to megger to ground.

Obviously and cables, busway, switchboards, motors and any distribution or utilization equipment suspected of having a short should be meggered.

With Electrical Preventative Maintenance (EPM), large distribution equipment should be meggered prior to and after service. Should there be a drastic change in readings you will realize you have possible made an error in your service or if the switch board has an existing problem you avoid being blamed for affecting the integrity of the switchboard. I am sure all of us have heard at least once “It worked when you got here”.

Prior to megging at a high voltage it is wise to either megger at 100 VDC or use an ohm meter to verify there are no loads on the equipment to be meggered, Protective relays, metering hidden bus taps, or customer utilization loads. If you obtain a reading LOCATE the load, sometimes this takes some perseverance.

What you should see:

We like to see full scale readings, 2000 megohms use to be the standard for most meggers but now meggers come with any were from 1000 megohms to 1000 gigohms full scale.

A simple test is to turn the megger and grab the test leads (NO JUST SEEING IF I HAVE BORED YOU TO SLEEP). With the megger on leads separate push the test button, air is an insulator and the reading should be full scale, touch the leads dead short megger should read zero (0). Take a piece of paper the thinner the better, using a pencil make a scratchy drawing all over with two heavy squares on the edge about 4” apart. Connect your megger and megger the paper at 1000 VDC, you should see arcing and may set the paper on fire or the arcing may burn the short free.

While some standards list .5 megohms (500,000 ohms) as acceptable, we like to see at least 5 megohms (5,000,000 ohms), 50 megohms is preferable (50,000,000 ohms) But if this is new equipment one would expect to see full scale readings, often refered to as infinity. It really not infinity your meter just does not have high enough resolution.

If the reading on A phase to ground is 50 megohms and B and C phase are 1000 megohms, the A phase should be checked for issues. With all things the same Temperature, humidity, age of equipment, and environment (dirt dust ECT) readings should be close.

Readings are taken A to B, B to C, C to A, and A, B, C and sometimes neutral to ground.
It is also a common practice to ground the phases not under test. Except motors and transformers.

Long cable runs and busway may take a while for the test voltage to charge the conductors under test. The conductors are a large capacitor and when the readings stabilize and max out the readings is recorded. This conductor MUST BE DISCHARGED to ground after test unless you want to receive a nasty shock.

Megger readings that do not stabilize, but fluctuate are indicative of moisture in or on the conductors and should be investigated. Sometimes this reading will continue to climb as the moisture evaporates due to the test voltage.

When meggering one must be careful with the voltage levels you are trying to prevent future electrical damage to cause it.


I use 5 different meggers, two are pictured below. All the meggers we use are digital some with an analog scale. We calibrate all our test equipment and meters yearly.

The f1st megger is a simple compact 1000 VDC go, no go megger for day to day use.

The 2nd megger I use has 50, 100, 250, 500 and 1000 VDC. I like this meter because of the 50 and 100 VDC settings.

The 3rd megger I use a hand crank model, I keep this on my truck for emergencies (LIKE DEAD BATTERIES).

The 4th megger is a 5KV (5000 VDC) with 1000, 2500 and 5000 settings, this meter is a battery and 120 VAC powered, the advantage is this meter hasa run timer for different test that require time test. Some spec. jobs require a one minute test for feeders.

The 5th megger is a ESI (Electric Static) tester with 10 and 100 VDC settings and a built in hygrometer and thermometer.

The last meter shown is a thermometer/hygrometer for measuring temperature and humidity


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## brian john (Mar 11, 2007)

Megger test at 1000 VDC utilizing a number 2 pencil, click twice on the picture.


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## brian john (Mar 11, 2007)

Missing a few pics

Small inexpensive 1000 VDC go no go megger.









.250KV, .500KV, 1KV, 2.5KV, 5KV megger











hygrometer


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## chrisb271 (Jul 6, 2007)

brian john said:


> Few electricians in America know what meggers are much less how to utilize one.



Well now that does surprise me !

Don't want to confuse the issue here BUT i've always known them as ' insulation resistance tester ' 

The word 'Megger' being a brand name in the uk even though a lot of other electricians do call them that

So you guys don't do regular inspections on electrical circuits and use an insulation resistance tester (megger) and record the results ?

In the uk we (or we should) do regular testing and inspections on both industrial and domestic wiring systems and compile a report on their condition and this tester is always used.


The test periods are -

A domestic (house) every ten years
This varies with a rented property to a test being done on every tenancy change.

industrial/commercial every five years

Bars and clubs every year

Temporary structures ( site huts on building sites ) Every three months.

Regards 

Chris


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## chrisb271 (Jul 6, 2007)

Ps

What are wire nuts ?


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## MDShunk (Jan 7, 2007)

chrisb271 said:


> In the uk we (or we should) do regular testing and inspections on both industrial and domestic wiring systems and compile a report on their condition and this tester is always used.


No, but I wish we did. About the only time I get to do that on a home is when there was a lightning strike. Because we don't have switches and fuses at each receptacle like you all seem to do, it's a very, very time consuming process with US wiring schemes. Removing GFCI's, light bulbs, dimmer switches, low voltage lighting transformers, etc. has to take place first. I've spent near a week meggerring out a single home already. Spent most of a day at a simple apartment once checking things out with the megger after a bad roof leak.


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## brian john (Mar 11, 2007)

Much as you call a vacuum cleaner a HOOVER, we call an insulation resistance tester a Megger. Or a over potential resistance tester.

And no our electricians seldom test anything unless forced too. I have had electricians call me a HACK, a RIP OFF / thief, a Witch Doctor and been told I am full of S**T. Yes by licensed qualified (?) electricians.


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## chrisb271 (Jul 6, 2007)

Well it just shows the differences in our lingo.

The in word for a vacuum cleaner now is Dyson ha ha.

No doubt you have seen the words "niccy" or "NIC" mentioned on here from the UK electricians well they are an organisation that regularly inspects electrical contractors to

" Ensure that they are doing the testing properly and to their standards "

Infact contractors that DON'T inspect and test are treated with scorn ! ha ha strange !

I used to work for a company and thats all i used to do , Inspect and test installations for safety.

regards

Chris


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## frank (Feb 6, 2007)

It's weird Chris. Not having a _Megger_ in your tool box is like not having your pants on _Meggers _and Electricians just go hand in hand here in the UK as you know. It must be because of the 'insulation test results we have to produce that has developed this practice.
A couple of weeks ago I dropped by AVO/ MEGGER in the washing up bowl in a Site Office. Didn't do it any good so I replaced it with a Fluke. First one ever - and though short on some functions I am quite impressed.

Frank


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## brian john (Mar 11, 2007)

Washing up bowl = SINK


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## frank (Feb 6, 2007)

Sink - to go down to the bottom.

Thanks Brian. The difference list is endless!


Frank


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## chrisb271 (Jul 6, 2007)

Aww Frank i had an AVO until recently,i had to lay the old girl to rest after she slipped into an open tank of hydraulic oil 

I was gutted,like losing an old friend,would have sooner lost my own arm,we had done some verifying together :laughing:

I also got myself one of those flukes,the multitesters,the very one that i said i would never get !

i got talked into buying it by the whippersnappers i have working for me now 

"its the way forward " " its no use living in the past " were some of the comments so i got the bull by the horns and got it on a deal with the wholesaler.

I hate to admit it but it is easy to use !

I just hope my old AVO has gone to electronic heaven :laughing:



Chris


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## shedfull (Aug 15, 2007)

brian john said:


> And no our electricians seldom test anything unless forced too. I have had electricians call me a HACK, a RIP OFF / thief, a Witch Doctor and been told I am full of S**T. Yes by licensed qualified (?) electricians.


 
Don't test unless forced to?    no wonder Brit spark's are sought after.:thumbsup: 

Lee


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## MDShunk (Jan 7, 2007)

shedfull said:


> Don't test unless forced to?


Yes, that's no kidding. In production oriented, new-construction type electrical contracting businesses, a guy would probably get fired for "wasting time" meggerring his newly installed wiring. On large work, normally only the heavy stuff gets meggerred.


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## shedfull (Aug 15, 2007)

So, what is the usual testing procedure in the States ?


Lee.


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## brian john (Mar 11, 2007)

Shed:

Let me see AHHHHHHHHH NONE, NIL, ZIP, ZERO, turn it on if it blows shake your head and try to blame someone else. UNless the specs call for testing and you get caught not following the specs.


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## Andy in ATL (Aug 17, 2007)

Bryan John's right- I'll reiterate, I'm new on the commercial side. I've never even heard of meggering in many years of resi. work and never with the shop i'm at now. I've been involved in several 300-600kcmil pulls and no one ever sweated it! It would seem prudent to test though if you had all these nifty things to test with. The shop i'm at is 150+ strong, makes gobs of money and does gov. as well as private industry. Where's the common sense?


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## MDShunk (Jan 7, 2007)

Andy... I think it's safe to say that if you pull a feeder for more than 480, somebody's going to be meggering it, among other tests. At least I hope so.


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## brian john (Mar 11, 2007)

Marc..In my expierence NOPE.


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## Andy in ATL (Aug 17, 2007)

Marc- I wish I was joking but I'm not. This is a LARGE shop- 150 +/- in the field and doing service and i've never even heard it mentioned. It would seem to me that even 480V should be meggered. We are talking big money pulls and equipment that some of this stuff feeds in the 10's of millions of dollars.


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## chrisb271 (Jul 6, 2007)

In the UK the electricity company used to 'megger' out the installation before they connected it to the mains,that all changed in the late 80's early 90's,more of it was shifted onto the contractor and made his responsibility.

Today i carried out an inspection of a four bed house that has just been wired by my lads.

Its getting to the stage in the UK that if you don't have your house or property regularly inspected and tested then you would find it very difficult to sell up,the emphasis is on test results and documentation.

Chris


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## wayni (Aug 27, 2007)

MDShunk said:


> Yes, that's no kidding. In production oriented, new-construction type electrical contracting businesses, a guy would probably get fired for "wasting time" meggerring his newly installed wiring. On large work, normally only the heavy stuff gets meggerred.


Hence the American term, "Smoketest".


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## geeyathink (Jul 29, 2007)

Hey all, I know this is an old thread but it seems like a good place for my question.

Is the difference between testing between wires with a standard ohmmeter and a megger the idea that 500 volts from a megger will "jump a gap" that the smaller voltage from a regular ohmmeter won't?

Pardon my stupidity, but I don't remember having seen it put into laymans terms.
I have read "A stitch in time" but its been a while.


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## Roger123 (Sep 23, 2007)

frank said:


> It's weird Chris. Not having a _Megger_ in your tool box is like not having your pants on _Meggers _and Electricians just go hand in hand here in the UK as you know. It must be because of the 'insulation test results we have to produce that has developed this practice.
> A couple of weeks ago I dropped by AVO/ MEGGER in the washing up bowl in a Site Office. Didn't do it any good so I replaced it with a Fluke. First one ever - and though short on some functions I am quite impressed.
> 
> Frank


Hi Frank,
I'm looking at buying a Fluke Megger, (Megohmmeter). Model 7Z1507, Test Voltages:50/100/250/500/1000 at $419.00 USA dollars. What to you think? Is that the one you purchased?


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## Roger123 (Sep 23, 2007)

Also,

Brian,

Very nice & informative post. I printed the post for future use, thanks.


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## Roger123 (Sep 23, 2007)

frank said:


> Sink - to go down to the bottom.
> 
> Thanks Brian. The difference list is endless!
> 
> ...


Damn, and we use to be ruled by you guys??? :blink:


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## brian john (Mar 11, 2007)

The difference is the higher the voltage the more it stresses then insulation. basically it JUMPS the gap.

Show me any PERFECT electrical insualtion and with enough voltage it can be broken down.


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## te12co2w (Jun 3, 2007)

I have to admit I am one of those electricians that doesn't carry megger around. I know I have a couple hiding somewhere, one crank model and another electronic one, but they don't live on the truck. After seeing this conversation maybe I'll be convinced to carry one around. I can see the potential for a lot of use with the upcoming AFI circuits. Prices I have seen aren't real bad unless I needed the 5000v type. That price takes my breath away.


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## geeyathink (Jul 29, 2007)

Thanks brian john,


Is it safe for both pieces of equipment and myself, to use a standard voltmeter to check the output of my megger?
Would I get an accurate reading?

I would throw this one away before I paid to have it tested. The guy looked to me like he needed a fix of something, so I took a chance and believed him when he said it works, he just needed some cash right away.

It is a cheapo (Amprobe AMB-3) but it looks new. I suspect its a piece of junk @ $90.00 new I can't see it being good for much but I had been pricing them again (thanks in large part to this thread) and wound up giving $30.00 for it.

Thanks for any responses, even if its "you paid $29.95 too much"


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## MDShunk (Jan 7, 2007)

geeyathink said:


> Is it safe for both pieces of equipment and myself, to use a standard voltmeter to check the output of my megger?
> Would I get an accurate reading?


For the meter you're talking about, just hold each lead and have someone briefly press the test button. That ought to tell you if it's putting out or not. Make sure it has fresh batteries.


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## geeyathink (Jul 29, 2007)

Thanks Mad Dog, that's about what I figured. 


I am going to have to wait to get a real one, I just ordered my IR thermometer and have to wait till my wish fund is replenished. Darn it.


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## 480sparky (Sep 20, 2007)

geeyathink said:


> I just ordered my IR thermometer and have to wait till my wish fund is replenished. Darn it.


Is your 'wish fund' seperate from your 'Christmas wish list'???


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## geeyathink (Jul 29, 2007)

Total different list.

As a budding tool hound I think I would shrivel up and die if I had to wait for Christmas every year!


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## brian john (Mar 11, 2007)

A DMM connected to the output of a megger will read the meggers output. If you use the VDC scale.


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## geeyathink (Jul 29, 2007)

Thanks brian john,

I may check this one for grins, but its good to know for when I get a real one.


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## Papa Smurf (Oct 5, 2007)

*Test in USA*



brian john said:


> Shed:
> 
> Let me see AHHHHHHHHH NONE, NIL, ZIP, ZERO, turn it on if it blows shake your head and try to blame someone else. UNless the specs call for testing and you get caught not following the specs.


 
Most Cities in the US Have an inspection dept. that inspects all jobs. It has different departments for Electrical, Mechanical, Structural and Plumbing.
The Electrical inspector looks at the walls before the sheetrock or paneling goes up to make sure everything secure and properly installed to code. In buildings with a layin type ceiling he inspects above ceiling before int layed in to make sure all is up to code. Then he comes back to do a final before the power is turned on. During the final he checks the neutral for grounds.
If the building is large as in a hospital floor remodel that has power in the building he will check every outlet with a plugin tester for correct wiring. all GFCI's for correct operation. If the job has an electrical engineer he also does walk throughs on a regular basis. At least thats the way it is done in Alabama. Which is a southern state that most folks up north think is full of ******** and dumb asses.


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## Papa Smurf (Oct 5, 2007)

*over 480 test*



MDShunk said:


> Andy... I think it's safe to say that if you pull a feeder for more than 480, somebody's going to be meggering it, among other tests. At least I hope so.


 
On jobs I have done all feeders over 600v are tested with a Hipot machine.
I will megger any feeder that is over 200 amps. I use the hand crank style.
Motor problems are easy to isolate with a megger. I use mine for mostly in trouble shooting.


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## JohnJ0906 (Jan 22, 2007)

Papa Smurf said:


> At least thats the way it is done in Alabama. Which is a southern state that most folks up north think is full of ******** and dumb asses.


A little touchy, are we? 

Welcome to the forum! :thumbsup:


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