# still waiting on that Megger Essay..



## Forgery (Mar 6, 2010)

http://www.electriciantalk.com/f2/gfci-breaker-good-bad-11810/index2/#post188077


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## charlie Bob (Jul 26, 2009)

Forgery said:


> http://www.electriciantalk.com/f2/gfci-breaker-good-bad-11810/index2/#post188077


Yeah i already seen that one.I want more though. I know Marc has some more in store.


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## Mike_586 (Mar 24, 2009)

http://www.biddlemegger.com/biddle/Stitch-new.pdf


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## charlie Bob (Jul 26, 2009)

Mike_586 said:


> http://www.biddlemegger.com/biddle/Stitch-new.pdf


thanks mike. I've already read it.It's pretty good.
But i'd still like to see a MDShunk essay on the subject.I know he's got a bunch of experience with it on the field.(he3's probably even meggered he's cat already:laughing
I know it would be a hit if he writes one.Lets all give him a push.


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## brian john (Mar 11, 2007)

You post questions I'll post answers.


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## 480sparky (Sep 20, 2007)

brian john said:


> You post questions I'll post answers.


 
Can you tell us how to use a megger properly? :whistling2:


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## NolaTigaBait (Oct 19, 2008)

brian john said:


> You post questions I'll post answers.


How long should I typically megger nm cable? I usually load it for about 20 seconds or so...It seems like it either goes to max value really quick or it slowly works it way to max....Is 20 seconds too short of time?


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## 480sparky (Sep 20, 2007)

charlie Bob said:


> ...........he3's probably even meggered he's cat already........


You didn't know that the MD in MDShunk stands for 'Megger Dis'?


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## charlie Bob (Jul 26, 2009)

brian john said:


> You post questions I'll post answers.


Brian i didn't mean to leave you out, you've been a great help to me when i first got my megger and all. You answered all my questions at the time.:thumbsup:
I know Marc has used his megger in residential a whole bunch and thought an essay on the experiences, numbers, trouble, etc he encountered would be great.

Now i do have a question:
I was talking to this older electrician one time, he never heard of a megger before, he has about 25 years experience he said. So he was quick to descredit the use of it.
Ater i explain the adventages and use of it, he asked me: " well, the insulation is stripped at every receptacle and device, so how would the megger readings be effective if so?"

Here's what i said:
"you megger between H-G,N-G,H-N(if you are sure there's no loads downstream), so since you are checking for any leakeage between the conductors insulation, at the receptacle or device the sonductor stripped ends on a terminal, which is away from the other conductor terminal your meggering."

Brian Does this answer sound correct to you?

Thanks.


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## charlie Bob (Jul 26, 2009)

NolaTigaBait said:


> How long should I typically megger nm cable? I usually load it for about 20 seconds or so...It seems like it either goes to max value really quick or it slowly works it way to max....Is 20 seconds too short of time?


Actually i was told by Brian, if my memory still works fine, that a minute is more than enough in residential applications.


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## charlie Bob (Jul 26, 2009)

480sparky said:


> You didn't know that the MD in MDShunk stands for 'Megger Dis'?


Is that right?, I sure didn't.


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## brian john (Mar 11, 2007)

charlie Bob said:


> Is that right?, I sure didn't.


MD stands for Maryland and Hunk = a stud so Marc 

MD's HUNK. Maryland's stud:laughing::laughing::thumbup::thumbup:


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## 480sparky (Sep 20, 2007)

charlie Bob said:


> Is that right?, I sure didn't.


 
No, I'm sure it stands for Marc, and the D stands for whatever his middle name is.


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## charlie Bob (Jul 26, 2009)

Brian, did you see my question for you. Look at post #12.
Thanks


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## MDShunk (Jan 7, 2007)

Yeah, I've actually been thinking a lot about that, and similar things lately. I'm probably going to open an informational website of my own here soon. It will be simple, and modeled after http://www.toad.net/~jsmeenen/ ,which is a site of a friend of mine. It's basically purely informational, and all text and pictures. I intend to make it so that mobile devices can display the website quickly (no long load times) and easily see it on the screen. 

For now, I'd say that you've got all the information you need on megger use. Brian and I have certainly written enough about it on forum posts. I've got some more information sprinkled on other forum sites, so just Google 'megger mdshunk'. I've used the same user name on pretty much all the forum sites, except for a couple that make you sign up under your full name (Marc D. Shunk). I suppose I could be Maryland's hunk, but I've never lived in Maryland. I'm also not much of a hunk, except to ugly women who have had too much to drink.


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## nrp3 (Jan 24, 2009)

I took some of the info and put it on a post it note. I stuck the post it note on the Stitch in time booklet that goes with the megger. I think what I need is some more experience with it. It would be nice to be able to pull some of the romex out and be able to say here is the problem. I have a bunch of poles to fix when the ground thaws, a bunch of bad UF to try it out on.


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## charlie Bob (Jul 26, 2009)

MDShunk said:


> Yeah, I've actually been thinking a lot about that, and similar things lately. I'm probably going to open an informational website of my own here soon. It will be simple, and modeled after http://www.toad.net/~jsmeenen/ ,which is a site of a friend of mine. It's basically purely informational, and all text and pictures. I intend to make it so that mobile devices can display the website quickly (no long load times) and easily see it on the screen.
> 
> Thank you Marc. I'll be looking forward to checking out your website whe ready.


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## nrp3 (Jan 24, 2009)

As a side note, I wonder how long it will be before we are forced to buy and use those testers that the Europeans have to use. They look cool but pretty pricey.


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## charlie Bob (Jul 26, 2009)

nrp3 said:


> As a side note, I wonder how long it will be before we are forced to buy and use those testers that the Europeans have to use. They look cool but pretty pricey.


What tester are you talking about?


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## MDShunk (Jan 7, 2007)

nrp3 said:


> As a side note, I wonder how long it will be before we are forced to buy and use those testers that the Europeans have to use. They look cool but pretty pricey.


They don't really use anything fancy. It's just a megger. They also use PAT testers (portable appliance testers), but we have those available too. It's basically a megger with some special features to make it easy to check appliances. They're not that expensive. The Europeans have special requirements to test the wiring in public buildings at regular intervals. I think for the most part, private dwellings are not really checked at any regular interval, unless work is being done, or maybe rentals. I forget.


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## nrp3 (Jan 24, 2009)

Fluke 1650 series, Megger and others I think. Have to dig a little on the US Fluke site to find info, but its in there in some of the tech papers.


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## brian john (Mar 11, 2007)

A quicky

For 600 VAC and lower systems

I perform these test at 1000 VDC after verifying no loads are connected. Time frames very with type of test, go-no go short conductor runs 30 seconds to a minute (when the meter reaches a stabilized reading) and or long runs of cable or busway, which can require 5-10 minutes. Minimum readings are published in NETA specifications. The often-quoted one (1) megohm is, in my opinion a mistake, 5 megohm would be a minimum under certain conditions (buried cable, emergency situations on 208/120 VAC systems). 50 megohms is a minimum we prefer with 100 megohms being the norm. BUT on new systems one would expect and hope to see full scale of the meter. At one time this full scale was typically 2000-4000 megohms, today that varies with the manufacture some meggers now read into gigohms and teraohms. One item to consider is comparison readings, such as a 3-wire circuit “L1” reads 2000 megohms; “L2” reads 200 megohms and “L3” reads 2000 megohms. While not a major issue I would want to know why “L2” was low. This would hold true for any type of circuit with similar conductors.
When Meggering it is important to verify all loads are turned off epically where there is sensitive electronics. You can damage this equipment or at a minimum get false readings.

Typically start with the lowest voltage your megger has, starting at 50, 100 or 250 VDC will minimize any chance of damaging equipment.

For trouble shooting single phase, I would megger Line to ground, line too neutral, neutral to ground. Typically when trouble shooting this is a go no go test allow megger reading to stabilize, no reason to wait one minute.

For new houses with no loads on (and smokes and similar equipment disconnected]
And the neutral bond lifted, I megger the panel with the meter lifted and all CB’s off for one minute, “L1” to neutral and ground, “L2” to neutral and ground, Megger neutral to ground.

As for exposed copper at terminals, this does nothing to the readings unless there is a problem with the terminal, such as some conducting medium between the terminal and ground or another polarity.

We megger everything and document all readings:
All new installations at a standard time frame (minimum one minute). We do gear separate from feeders prior to termination.
All equipment serviced once again at one-minute minimum, we like to megger when de-energized and prior to re-energizing to verify we did not screw up. Plus if you get low readings with the first reading the customer MUST be aware of this, because human nature would be to blame you if you just megger at the end of service.
Houses after a lightning strike, with separate readings for the panel, then individual branch circuits, then the completed system.
Neutrals for all services worked on to determine if there are down stream shorts.


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## MDShunk (Jan 7, 2007)

charlie Bob said:


> Thank you Marc. I'll be looking forward to checking out your website whe ready.


I've got more ideas than I have hours in the day. Just like anyone else, I have certain things I must do today, certain things I want to do today for fun and relaxation, and certain things I'd like to do sometime. The list of things I'd like to do sometime is lengthy. The list of things I must do on any given day generally takes up most of the day.


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## nrp3 (Jan 24, 2009)

I thought, probably mistakenly, that it was a dwelling thing. Maybe French Electrician or some of our English counterparts will share some info.


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## NolaTigaBait (Oct 19, 2008)

MDShunk said:


> I've got more ideas than I have hours in the day. Just like anyone else, I have certain things I must do today, certain things I want to do today for fun and relaxation, and certain things I'd like to do sometime. The list of things I'd like to do sometime is lengthy. The list of things I must do on any given day generally takes up most of the day.


I bet you have all kinds of crazy chit rolling around in your head.


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## MDShunk (Jan 7, 2007)

I know that UK user Frank has written on their test procedure and the intervals for various types of occupancies. You might use the Search button and look for a post with the key word "club" for user Frank.


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## nrp3 (Jan 24, 2009)

Brian or anyone else who cares to elaborate, when you mentioned testing the panel, how are you testing? With the main and all branch breakers off, testing after the main but before the branch breakers or maybe on the load side of the meter? Are we looking for the 100 meg or better readings?


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## NolaTigaBait (Oct 19, 2008)

nrp3 said:


> Brian or anyone else who cares to elaborate, when you mentioned testing the panel, how are you testing? With the main and all branch breakers off, testing after the main but before the branch breakers or maybe on the load side of the meter? Are we looking for the 100 meg or better readings?


Check that thread that was posted on the 1st page, Marc listed all of his minumum values.


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## MDShunk (Jan 7, 2007)

nrp3 said:


> Brian or anyone else who cares to elaborate, when you mentioned testing the panel, how are you testing? With the main and all branch breakers off, testing after the main but before the branch breakers or maybe on the load side of the meter? Are we looking for the 100 meg or better readings?


I suppose everyone has their own style, but here's what I do...

Turn off main and all branch breakers. 

Meg from each leg of the LOAD side of the main to the neutral bar then each leg to the ground bar (bond lifted, of course). That will tell you if you've got a problem in the panel or not. Beware of GFCI and AFCI breakers. You need to take their neutral pigtail off the neutral bar before you meg the panel hot to neutral, or you stand a chance of zapping your high-dollar AFCI's and GFCI's into oblivion. 

Now, turn on all the branch breakers, and repeat that test. That will tell you if you've got a problem on at least one of the branch circuits. 

If you do seem to have a problem on one of the branch circuits, lift the wires off the load side of all of the branch breakers a meg from that wire to neutral and that wire to ground. That will pin down the branch circuit(s) with an issue. Divide and conquer the nonconforming branch circuits out in the house, wherever they might be, to find the problem.

Keep in mind, loads like light bulbs, smokes, GFCI's, chime transformers, photocells, motion sensors, furnace control boards, attic fans, etc. will cause false shorted readings, so these loads need disconnected from the branch circuit for branch circuit testing. This equipment needs checked individually.

For instance, you'd meg an attic fan from each motor lead to the fan's metal case. You cannot summarily dismiss a load as not being a problem just because you disconnected it to meg the branch circuit.


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## 480sparky (Sep 20, 2007)

MDShunk said:


> I suppose everyone has their own style, but here's what I do.............


Just a suggestion........... but can you make this and Brians' post a Sticky Note?


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## MDShunk (Jan 7, 2007)

480sparky said:


> Just a suggestion........... but can you make this and Brians' post a Sticky Note?


Probably, but I'm not sure I know how. Let me check. Speedy is more of the the official sticky maker person.


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## MDShunk (Jan 7, 2007)

Okay, it seems you can't make posts sticky, but you can make a thread sticky, so that's what I did... for now. It's sort of against our moderator rules to stick threads without admin permission, but I've always found it easier to ask for forgiveness than ask for permission. :laughing: Sort of the old shoot first, ask questions later idea.


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## brian john (Mar 11, 2007)

I would suggest that anyone involved in testing any electrical systems were documentation is required or customers are concerned with adherence to set Standards download the complete NETA documents.

http://www.netaworld.org/

Cables 600 VAC and under

Perform insulation-resistance test on each conductor with
respect to ground and adjacent conductors. Applied potential
shall be 500 volts dc for 300 volt rated cable and 1000 volts​dc for 600 volt rated cable. Test duration shall be one minute.

Circuit Breaker test (MEGGER ONLY LISTED BELOW)

Perform an insulation-resistance test at 1000 volts dc
from pole-to-pole and from each pole-to-ground with
breaker closed and across open contacts of each​
phase


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## frenchelectrican (Mar 15, 2007)

I know someone did mention my name here and asked for the megger test requirement in European area.

Between the USA side and Europe side requirement for megger test is not a huge diffrence how to use it both are the same way.

However Brian John and MDshunk both did cover the subject very well.

Basically that what I do the same way as Brian John however in Europe area it more common to have megger test everytime we get done with new circuits or repaired circuits.

And anytime before new service is hook up we have to run the megger test to verfiy everything is correct and meet the European regulations.

I do carry couple megger testing devices with me I have a simple go / no go megger tester { that is most common one I use for basic test } but if more than a simple test or in commercal location then I go with real deal megger tester to read the megaohms plus voltage level that I am running on it.

As far for UK requirement I will let the UK guys give you the straght facts due I know the UK regualuations change a bit.

But for my French requirement we must have to run the megger for minuim of 1 minuites but most case useally 2 minutes unless it is underground run then I bump up to 2 1/2 minutes the max.

All the resdentail and light commercal test that based on either 500 V DC or 1000 V DC depending on which suppy it have on the location.

If other question just holler one of us will be more than happy to answer your question.

Merci,Marc


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## brian john (Mar 11, 2007)

If installed at the panel, keep the conductors as straight as possible, cable tie them together and as short as possible.


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## shieldcracker (Sep 14, 2009)

RCD meters


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## MDShunk (Jan 7, 2007)

shieldcracker said:


> RCD meters


Three-handled family gredunza


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## 76nemo (Aug 13, 2008)

MDShunk said:


> Three-handled family gredunza


 
What the???????:blink:


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## brian john (Mar 11, 2007)

76nemo said:


> What the???????:blink:


11 or 80 to the hour.

Or was it 25 or 6 to 4?


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## 76nemo (Aug 13, 2008)

brian john said:


> 11 or 80 to the hour.
> 
> Or was it 25 or 6 to 4?


I don't have a flyin' hootenanny as to what your are referring to Marc/Brian.

Last laugh's on me. I know what RCD's are. How did we go from a discussion on IR to RCD'S:blink:???????????????????


25, 6 or 4? Chicago??:laughing:


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## Introyble (Jul 10, 2010)

charlie Bob said:


> MDShunk, i was brousing on some old megger posts, and I came across one where you say that ,quote" ... Maybe I should write a short essay on using one for troubleshooting one day. "
> Hey I'll be the first one to read it if you ever have some time to write it.
> I thought that maybe having somebody reminding you about it, would give you a little push


Leave all conductors on the VFD and turn the meter to the maximum setting and you should be just fine!


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## shieldcracker (Sep 14, 2009)

76nemo said:


> I don't have a flyin' hootenanny as to what your are referring to Marc/Brian.
> 
> Last laugh's on me. I know what RCD's are. How did we go from a discussion on IR to RCD'S:blink:???????????????????
> 
> ...


Well my comment was made after a short post, #20 to be exact, Not as short as NY minute but anything can change.:laughing::laughing::laughing:


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## Motorwinder (Dec 30, 2010)

Fluke and Sperry are my meggers. 

I megg for 1 min to let stabilize and polarize.

I once megged a 4160 volt motor at .1 meg, and the customer left it in service.

Most these gearless elevator DC motors on the sky scrapers are running under 1 meg. If they're over .1, the customers a happy guy.


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## Ouch_That_Hurt (Aug 20, 2010)

*Megger Book*

This is a great book about Megger's.

http://www.maintenancegeeks.com/downloads/doc_details/264-megger-astichintime


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## The_Modifier (Oct 24, 2009)

Ouch_That_Hurt said:


> This is a great book about Megger's.
> 
> http://www.maintenancegeeks.com/downloads/doc_details/264-megger-astichintime


See post #3.:whistling2: Bookmarked that website, handy manuals all over it, ty.


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## tgreen (Sep 14, 2010)

I am supprised that a post on how to us a megger properly has gained so much interest. i would expect that as a Journeyman/Master electrician/contractor that the use of a megger would be well understood.


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## BBQ (Nov 16, 2010)

tgreen said:


> I am supprised that a post on how to us a megger properly has gained so much interest. i would expect that as a Journeyman/Master electrician/contractor that the use of a megger would be well understood.


You would be mistaken, many electricians do not own mega meters and will never use one.


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## muck (Jun 30, 2008)

This might help some - 

http://www.allaboutcircuits.com/vol_1/chpt_8/7.html
http://www.allaboutcircuits.com/vol_1/chpt_8/7.html


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## brian john (Mar 11, 2007)

BBQ said:


> You would be mistaken, many electricians do not own mega meters and will never use one.


 
And many EC's hire out the meggering to testing firms, for a variety of reasons, spec's, unfamiliar with what the readings mean, saves them money in the short run. Though meggers have come down in price and are available everywhere these days.


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## tgreen (Sep 14, 2010)

I hire out for High Pot tests, because of the specialty equipemnt that is used, and the need for third party verification, but not for simple insulation testing and 600v cable. 
if your work is primarily residential i could see not using or needing a megger. but, if your a commercial/industiral electrical contractor the proper use of a megger, and knowing how to interpet the readings should perty standard.


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## brian john (Mar 11, 2007)

tgreen said:


> I hire out for High Pot tests, because of the specialty equipemnt that is used, and the need for third party verification, but not for simple insulation testing and 600v cable.
> if your work is primarily residential i could see not using or needing a megger. but, if your a commercial/industiral electrical contractor the proper use of a megger, and knowing how to interpet the readings should perty standard.


 
Maybe in Europe.


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## frenchelectrican (Mar 15, 2007)

tgreen said:


> I hire out for High Pot tests, because of the specialty equipemnt that is used, and the need for third party verification, but not for simple insulation testing and 600v cable.
> if your work is primarily residential i could see not using or needing a megger. but, if your a commercial/industiral electrical contractor the proper use of a megger, and knowing how to interpet the readings should perty standard.


 
For France side anything over 750 V AC or DC we do either megger or High Pot test depending on the set up. { under 750 V AC or DC we just run the megger that useally take care of it most of the time.}

But Tgreen., The UK and France and few other European countries are pretty strict with testing so we have to use the megger devices pretty often before we can able engerized it.

Merci,
Marc


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## Frank Mc (Nov 7, 2010)

Here in Oz our code book requires all new installations to be megged ,so i would assume all Domestic sparkies (residental) would (should) have a meggar..now referred to as Insulation Resistance Tester....

Frank


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## brian john (Mar 11, 2007)

I will say more contractors have a megger now, than in the past. Fully understanding their use, not so much.


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## tgreen (Sep 14, 2010)

maybe this is just another reason for a national standardized training and testing for journeyman/apprentice electricians. If i hire a Journeyman and tell him to go megger all the feeders in an MDP and then i have to teach him how to use a megger, i would not be happy. 
IMO this should be standard trade knowledge, if you want to be a journeyman. and if people have made it to the journeyman/master level and dont know how to use one, then that is just poor training


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## BDB (Jul 9, 2008)

brian john said:


> I would suggest that anyone involved in testing any electrical systems were documentation is required or customers are concerned with adherence to set Standards download the complete NETA documents.
> 
> http://www.netaworld.org/
> 
> ...


Even though NETA is the standards at which testing is graded by, I think NETA is just a "testing" country club. They make it where an electrical company can not gain membership to NETA. One of it's requirments is :

"A minimum of 75% of the companies gross income must come from the electrical testing and maintenance services listed on the full service check list."

To me this is just another way of saying, we do not care if you are qualified and are capable of testing you will not get certification from NETA unless you are in the good ole boys club.


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## macmikeman (Jan 23, 2007)

Once having fallen into the wrong hands, an insulation testing device is one of the best sales tools ever invented, especially the ones with neat little red, amber, and green led lights........ Kaching$$$:thumbup:


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## macmikeman (Jan 23, 2007)

By the way, what I do is no different than what Brian does, only a bit less sophisticated and to a different market........:thumbsup:


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## Resiwireman (Apr 27, 2011)

*Residential ?*



tgreen said:


> I hire out for High Pot tests, because of the specialty equipemnt that is used, and the need for third party verification, but not for simple insulation testing and 600v cable.
> if your work is primarily residential i could see not using or needing a megger. but, if your a commercial/industiral electrical contractor the proper use of a megger, and knowing how to interpet the readings should perty standard.


Is there any need for a Megger in residential ? I've used just a continuity test, for grounds, at the main pnls, or my circuit tracer for locating faults for many years now. My only exp. was when I was a helper to a high voltage High Pot test (hand cranked) for a 4160V line, for insulation weakness.


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## tgreen (Sep 14, 2010)

I cant think of to manny instances in the RESI market where you would need the use of a megger. But, i dont do any resi work. all of our work is commerical/industrial/gov contract. so in the work we do we have to turn in megger reports for every job. 

I use a NETA testing company to do some of my testing, but not for megger reports. the only place i might see needing a NETA testing company to do megger reports would be for the oil field work, and then the oil complany contracts that direct. the COE does like to witness our testing when we do work on the military bases.


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## BBQ (Nov 16, 2010)

Resiwireman said:


> Is there any need for a Megger in residential ? .


They can be used to find the causes of GFCIs and AFCIs tripping for no apparent reasons.


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## brian john (Mar 11, 2007)

Verifying the integrity of the wiring, assuring there are no neutral to ground issues and as BBQ noted.


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## 76nemo (Aug 13, 2008)

tgreen said:


> I cant think of to manny instances in the RESI market where you would need the use of a megger. But, i dont do any resi work. all of our work is commerical/industrial/gov contract. so in the work we do we have to turn in megger reports for every job.
> 
> I use a NETA testing company to do some of my testing, but not for megger reports. the only place i might see needing a NETA testing company to do megger reports would be for the oil field work, and then the oil complany contracts that direct. the COE does like to witness our testing when we do work on the military bases.


 
Tell* that* to the UK, and see how far you get...............


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## HARRY304E (Sep 15, 2010)

76nemo said:


> Tell* that* to the UK, and see how far you get...............


That will be good.


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## frenchelectrican (Mar 15, 2007)

tgreen said:


> I cant think of to manny instances in the RESI market where you would need the use of a megger. But, i dont do any resi work. all of our work is commerical/industrial/gov contract. so in the work we do we have to turn in megger reports for every job.
> 
> I use a NETA testing company to do some of my testing, but not for megger reports. the only place i might see needing a NETA testing company to do megger reports would be for the oil field work, and then the oil complany contracts that direct. the COE does like to witness our testing when we do work on the military bases.


BBQ did gave one good answer and I will tell you from France side we do have to megger everything from resdentail to commercal / industrail for safety issue and we do have to keep the records of it and what more many POCO in European side they will not hook up until you pass the megger testing.

I know our UK guys will tell you pretty much the same as I saying.

Merci,
Marc


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## tgreen (Sep 14, 2010)

I think megger testing should be done more often prior to egergizing a circuit. I know in my experience i have found a hand full of cables that with an ohm meter they tested good, but failed a megger test. and, im glad i did the testing a ground fault on those systems would have been a mess to fix. 
the only time i see megger testing required here in the US is for a few commerical companys, most industiral clients, and all the Government projects. 
I was suprised when i first read this thread that there were several Journeyman/master electricians that were not familiar with meggering cables. I was using a megger my first year in the trade. and yes i learned the hard way why you dont touch the leads while you are testing.


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## samkallis (May 3, 2011)

*cutter tools*

Spam and to add insult to injury it was off topic.


SPAM


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## johnsmithabe (May 3, 2011)

thank u MD


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## Joemoco (Jul 25, 2011)

Using a megger to find ground faults or phase to phase shorts is a useful tool.....but it must be done according to rating of insulation of wire,,,,and rule of thumb is one megohm per 1000 volts...sooo for example..a 480 volt motor would be questionable at less than a half a megohm......but I have also seen them run at less than a quarter of a megohm. When having these readings many times taking a moisture reducer...say a heat lamp...or light bulbs in series with the windings will dry out the motor and bring readings up after a while. But be careful betting on the outcome...its risky...but sometimes worth the effort when availability is scarce or delivery may be long.


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## brian john (Mar 11, 2007)

Joemoco said:


> Using a megger to find ground faults or phase to phase shorts is a useful tool.....but it must be done according to rating of insulation of wire,,,,and rule of thumb is one megohm per 1000 volts...sooo for example..a 480 volt motor would be questionable at less than a half a megohm......


Live by that number and watch the smoke and arcs.

I have on rare occasion energized something at 1 megohm or less and in each case the equipment did operate for a short period. Additionally these were underground cables.


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## AnthonyClifton (Sep 14, 2011)

I have never even seen a meggar. I've heard of them though.


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## dronai (Apr 11, 2011)

Will megger testing a branch circuit in an unoccupied residence, damage the gfi's ?


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## McClary’s Electrical (Feb 21, 2009)

dronai said:


> Will megger testing a branch circuit in an unoccupied residence, damage the gfi's ?


You don't megger a wire with gfi attached, 
1, you'll ruin the gfi
2, the readings will be useless


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## dronai (Apr 11, 2011)

So I have to remove all gfi's, and turn off all switch legs, so I don't blow out the bulbs. anything else ? megger at 500V for 5 seconds


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## brian john (Mar 11, 2007)

dronai said:


> So I have to remove all gfi's, and turn off all switch legs, so I don't blow out the bulbs. anything else ? megger at 500V for 5 seconds


 
Smoke detectors, appliances. 1000 VDC, NM is 600 VAC cable


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## dronai (Apr 11, 2011)

brian john said:


> Smoke detectors, appliances. 1000 VDC, NM is 600 VAC cable


 
Dimmers also ! Sounds like more work than I anticipated. Good way to check out the condition of the wiring for residential remodels.


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## dronai (Apr 11, 2011)

brian john said:


> A quicky
> 
> For 600 VAC and lower systems
> 
> ...


My megger only goes up to 500V


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## rdr (Oct 25, 2009)

brian john said:


> We megger everything and document all readings:
> All new installations at a standard time frame (minimum one minute). We do gear separate from feeders prior to termination.
> All equipment serviced once again at one-minute minimum, we like to megger when de-energized and prior to re-energizing to verify we did not screw up. Plus if you get low readings with the first reading the customer MUST be aware of this, because human nature would be to blame you if you just megger at the end of service.
> Houses after a lightning strike, with separate readings for the panel, then individual branch circuits, then the completed system.
> Neutrals for all services worked on to determine if there are down stream shorts.


Brian, I cut off most of your post so mine wouldn't be so long quoting you. I'm just wondering what situations warrant using a megger? I've never seen it done in electrical (I have for electronics but that's another animal) Do you do it just for troubleshooting, or new installations as well? When is "ohming out" your circuits with a meter not good enough?


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## knowshorts (Jan 9, 2009)

rdr said:


> When is "ohming out" your circuits with a meter not good enough?


I have had circuits look just fine while ohming them out, but show a definite fail with a megger.


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## brian john (Mar 11, 2007)

rdr said:


> Brian, I cut off most of your post so mine wouldn't be so long quoting you. I'm just wondering what situations warrant using a megger? I've never seen it done in electrical (I have for electronics but that's another animal) Do you do it just for troubleshooting, or new installations as well? When is "ohming out" your circuits with a meter not good enough?


We use a megger on all new installations, conductors, motors, switchboards. We also utilize a megger for maintenance and trouble shooting.

As for a ohm meter versus a megger. We have responded to several blow ups where the EC was going to re-energize a switchboard, based on his ohm meter, we megged the boards and they fail. Additionally we have had several cases where we were hired to look into the second blow up. The EC re-energized a board based on his ohm meter, with catastrophic results.


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## fondini (Dec 22, 2009)

rdr said:


> Brian, I cut off most of your post so mine wouldn't be so long quoting you. I'm just wondering what situations warrant using a megger? I've never seen it done in electrical (I have for electronics but that's another animal) Do you do it just for troubleshooting, or new installations as well? When is "ohming out" your circuits with a meter not good enough?


We megger the whole house after a fire also. Its a great tool!


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## dronai (Apr 11, 2011)

fondini said:


> We megger the whole house after a fire also. Its a great tool!


 
What Voltage do you use, and how many seconds ?


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## 76nemo (Aug 13, 2008)

rdr said:


> Brian, I cut off most of your post so mine wouldn't be so long quoting you. I'm just wondering what situations warrant using a megger? I've never seen it done in electrical (I have for electronics but that's another animal) Do you do it just for troubleshooting, or new installations as well? When is "ohming out" your circuits with a meter not good enough?


 
No, a DMM can't push the proper voltage levels to suffice in order to do proper testing. IRT is done for several reasons, installation, PM and service.

Because this thread has been dragged on for quite awhile, I'll keep this short. It seems apparent to me from some of the more recent posts some people think they can go in and knock out an IRT on certain feeds in a few hours or so and call it a bill. Depending on what, where and why the IRT is being performed, it can take much longer. It is not always a simple task. The technician needs to know exactly what he/she is looking at under specific conditions. You can't just go online or into the supply house, buy an insulation tester and go out and write reports. It doesn't work that way. Can you spend a few hours researching it on the internet and try and go perform proper testing at a facility? Not even remotely close. It is a skill......


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## 76nemo (Aug 13, 2008)

dronai said:


> What Voltage do you use, and how many seconds ?


What is the cable rated at? You start there.........


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## dronai (Apr 11, 2011)

76nemo said:


> What is the cable rated at? You start there.........


600V, 

In the post, Brian John said megger at 1000Vdc for 30 seconds to a minute. I was just cuious about how other people are doing it.


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## frenchelectrican (Mar 15, 2007)

dronai said:


> 600V,
> 
> In the post, Brian John said meeger at 1000Vdc for 30 seconds to a minute. I was just cuious about how other people are doing it.


 
Dronai .,

For 600 volt class cable I useally set for 1 KV but do not run the megger more than 1 maybe 1 1/2 min the most.

With very good cable or conductors you should get more than 500 megaohms at the prescribed time as I mention.{ 500 Megaohms is a kinda a guideline depending on length of conductor } 

This method I have done all the time in France it is a SOP.

Merci,
Marc


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## nrp3 (Jan 24, 2009)

By the way, is there any such thing as a reasonably priced megger with over 1000v? I was looking at two brands of heat tape for a roof and one calls for meggering at 500,1000,and 2500v. Naturally mine only goes to 1000v. This is expensive stuff and adding another $1000 to an already pricey job, likely not to happen.


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## user8640521 (Jan 17, 2009)

brian john said:


> I will say more contractors have a megger now, than in the past. Fully understanding their use, not so much.


pretty much.... i worked in capacitor manufacturing before becoming
a sparky, so i've had more than passing experience with hipot and megger
testing....

when you are meggering *anything*, you are testing the dielectric strength
of the insulator, so you are in effect charging up the insulation as you would
a capacitor. longer wire, and heavier gauge wire take more time to charge up.

and wire to wire meggering takes longer than wire to ground, as you are
charging up twice as much dielectric.

i've meggered all sorts of stuff, including the bezel of a wet niche pool
fixture to the #6 bond of the ground grid for the pool, for an inspector
who wanted to know it was bonded correctly.....

the fluke handhelds, while not powerhouses have the ability to tell you
what the voltage across the leads is... when your insulation breaks 
down, you won't be able to pull 1,000 volts across it, you may get 775
volts, with 8 megs resistance, the rest is bleeding off.... as the insulator
is becoming a conductor... :-/

brian's field of work far surpasses most of ours in terms of testing i suspect....
when he or zog type, i read.


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## brian john (Mar 11, 2007)

FulThrotl said:


> pretty much.... i worked in capacitor manufacturing before becoming


That seem like a neat place to work for a while?



> when you are meggering *anything*, you are testing the dielectric strength
> of the insulator, so you are in effect charging up the insulation as you would
> a capacitor. longer wire, and heavier gauge wire take more time to charge up.


And the megger in use.

From NETA

7.3.2.2.2

2. Perform an insulation-resistance test on each conductor with respect to ground and adjacent
conductors. The applied potential shall be 500 volts dc for 300-volt rated cable and 1000 volts​dc for 600-volt rated cable. The test duration shall be one minute.
 

As for what we do, I read the specs first. Many have different times frames noted.

Or if it is a go, no go test. Hit it and run.


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## user8640521 (Jan 17, 2009)

brian john said:


> That seem like a neat place to work for a while?
> 
> 
> 
> ...


it was kinda fun... i got to work with vacuum tanks, pcb's on bare
skin, triclorethelene in 55 gallon barrels, high voltage AC and DC,
and OSHA was only a gleam in a politicians eye, mostly.

i also learned level ten black belt soldering from asian women...
one of them said that i was the only white guy who could swage
solder as good as an asian woman. it was 1974, and political correctness
hadn't been invented yet.

from days of yore... when i was hipotting, i'd have a fluke
bench meter across the test rack, and the timer started when i hit the 
test voltage. hipot was typically 125% of working voltage, for 30 seconds,
but could be specified up to 250%.. those were used on ballistic missle subs,
i believe.... and i took a bunch of them that had high dissipation factor and
weren't suitable product home, and made my first, and next to last, tesla
coil in the garage.... running on 220 volts from the dryer plug....

i didn't know about composite AC then, or harmonics, or a lot of
things. i was freaking lucky not to toast myself. shoot, i was 19
years old. i had opinions on everything unmarred by either fact or
logic.

not that much different than today... ;-)


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## Bighand (Feb 13, 2012)

OK I got to ask the question, why are you using a megger in residential applications? I’m sitting here next to another electrician and we are scratching each others head on that one. We work in an industrial environment that has the over use of water and we look for leakage all the time. I have been in the trade for 25 years and I would flip if I saw someone using a megger in a residential system.

Sorry I was just flipping through and came on to this thread and had to stop and ask.
:smartass:


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## parnellelectric (Dec 23, 2011)

Learned alot from this post, thanks. I think I will keep the megger out of residential. I have my own ways of finding problems. Usually starts with "what changes have been made lately"........... Would the megger find a flickering dawn to dusk cfl from lowes tripping a AFCI?


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## Big John (May 23, 2010)

So the other day I megged an old 600V stator at 1000V.

One of the guys mentioned he was pretty sure that would damage the insulation because of the age.

Just to double check: The 600VRMS rating only applies to heating, correct? That is to say, when you're actually figuring insulation stress during operation, the insulation is really seeing 848V (600*1.414)? 

If that's a true statement, I see no reason not to meg at 1kV regardless of age. Agree or disagree?

-John


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## brian john (Mar 11, 2007)

Big John said:


> So the other day I megged an old 600V stator at 1000V.
> 
> One of the guys mentioned he was pretty sure that would damage the insulation because of the age.
> 
> ...


The maximum AC voltage is as you noted 848 VAC. If the insulation was in such poor condition, that the 1000 VDC megger damaged it, it was time for replacement.


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## Big John (May 23, 2010)

brian john said:


> The maximum AC voltage is as you noted 848 VAC. If the insulation was in such poor condition, that the 1000 VDC megger damaged it, it was time for replacement.


 Thanks. That's was my logic, but I wanted to double-check with the gurus. :thumbsup:

-John


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## Zog (Apr 15, 2009)

FulThrotl said:


> when you are meggering *anything*, you are testing the dielectric strength
> of the insulator, so you are in effect charging up the insulation as you would
> a capacitor. longer wire, and heavier gauge wire take more time to charge up.
> 
> .


Actually a Megger tests the insulation resistance, not the dielectric strength. A hipot is one type of dielectric strength test per IEEE/ANSI definitions. A Megger, or IR test, is usually done prior to an overpotential or dielectric strength test to ensure the system will not be damaged by the overpotential test.


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## Pattester (Mar 8, 2012)

*PAT Testing*



MDShunk said:


> They don't really use anything fancy. It's just a megger. They also use PAT testers (portable appliance testers), but we have those available too. It's basically a megger with some special features to make it easy to check appliances. They're not that expensive. The Europeans have special requirements to test the wiring in public buildings at regular intervals. I think for the most part, private dwellings are not really checked at any regular interval, unless work is being done, or maybe rentals. I forget.


You're pretty spot on there,apart from a good PAT Tester can cost £1,000 plus Landlords Pat Testing usually every year , seems silly when the tenants items aren't normally checked for safety and they are usually the worst.:no:The fixed installation on rental properties need testing every 5 years,


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## The_Modifier (Oct 24, 2009)

Pattester said:


> Landlords Pat Testing


You link is dead?


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## Black Dog (Oct 16, 2011)

bump....


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