# Megger residential wiring



## 480sparky

Meggers indicate faults in the wiring's insulation. That's what will trip GFCIs, as well as many AFCIs as they have some level of GFCI protection built into them.


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## JBrzoz00

how do you use one? Would it be a good idea to megger the circuits after drywall and trim is installed in a home?


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## 480sparky

JBrzoz00 said:


> how do you use one? Would it be a good idea to megger the circuits after drywall and trim is installed in a home?


I use a Fluke 1587. I megger as the last step in rough-in, then first step during trim.


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## telsa

Meggers impose a test voltage -- and if you've got a touch of weak insulation -- the imposed voltage will bleed out -- and be detected by the Megger. (Think of a capacitor that is barely leaking charge.)

Meggers can detect such weaknesses in any dielectric -- within their range. In the normal course of events, these trivial breakdowns build and build until you have a "bolted short." Which is slang for "you might as well have bolted the conductors together... conductivity is sky high. "

Meggers can't normally suffer connected loads for the test. The voltages involved normally damage the load device // blow it up and in any event, the megger reading will be way off.

It is unusual for anyone to megger new Romex in a residential setting. The circuits are either good or the rockers got to them ! ( And they couldn't even survive the common plug tester. )

For myself, I give my feeder conductors the treatment,... and the Service busing.

Greenlee 5880.


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## EM1

A megger is simply a "megohm meter" and it only measures insulation resistance, at higher values than a regular ohm meter. Generally a regular DMM operates at 9VDC on the ohm scale. A megger will have selectable outputs of 50, 100, 250, 500, or 1000VDC to test insulation to ground or phase to phase as desired, at the proper voltage for the circuit under test. It will not pin point the spot of failed or failing insulation, it is not a fault locator. It will read the overall resistance to whatever you are testing to, then if you have low reading you still have to break the circuit into sections to find the problem conductor or device. Not normally needed for residential circuits unless you are troubleshooting a specific problem.


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## Bad Electrician

*Posted several times*

Megger testing is actually insulation resistance testing, I wrote several thing for ET on that topic hopefully someone will find and post the sticky.

Here is a starter

Questions often arise regarding the use of Meggers I have posted some information, that hopefully is useful. Some of the information noted below is based upon personal experience; all users should familiarize themselves with the correct test criteria and test equipment prior to performing any work. Testing is NEVER completed on energized equipment. If you are not sure about your results HIRE a company that has experience in the test you are performing or obtain help in determining the results prior to possible damaging yourself or the distribution system you are working on. Lastly NEVER rely on a continuity tester or ohm meter to check any distribution system for shorts/faults. This is a good way to damage the distribution equipment, hurt yourself or worse, end up on the wrong end of a lawsuit
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From Wikipedia:
A megger (or sometimes meggar) is often used as an alternate term for an insulation tester - a circuit tester which puts a very high voltage at a very low current across two conductors to make sure that they are properly insulated. The word is short for megohm-meter.
It is in fact the registered trade mark of Megger Group Ltd who have manufactured insulation testers since 1889.
Older types of insulation testers have a small built-in generator turned by the handle. Modern types work with batteries and circuitry to generate the voltage required.

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Megohm = 1,000,000 = one million ohms
Gigohm = 1,000,000,000 = one billion ohms
Terohm = 1,000,000,000 = one trillion ohms
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Today meggers typically come is 3 basic styles.
1. Analog and can be line voltage, battery, hand crank or a combination of two
2. Digital and can be line voltage or battery operated or both.
3. Digital with an “analog” scale these are also line voltage or battery operated or both.
Typical DC voltages available are 50. 100, 250, 500, 1,000, 2,500, 5,000 and 10,000 or some combination of these. 
A decent megger for the ‘average electrician” has250, 500 and 1,000DC voltage settings, though I really like a megger that has a 50 or 100 VDC test voltage (in addition to 250, 500 and 1,000 VDC settings)as it allows me to pre-test a circuit with a certain sense of I am not going to fry something sensitive. I also prefer a digital analog style meter.
There are additional megger types for special test, but I have not included these as they are outside the scope of what the average electrician should have in his “tool case”
See attached photos 
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Meggers can be utilized to test all distribution equipment with a few considerations.
1. Length of conductors will affect the readings and you need to take this into account that there is a time to charge the conductors (typical times are one minute).
2. Long conductor runs will “hold a charge” always ground the conductors after testing.
3. Readings that fluctuate often indicate moisture and/or water. Leaving the megger connected can in some cases “dry out the problem” Though if moisture or water is an issue obviously this warrants further investigation.
4. You have to be careful that all loads are disconnected, meters, relays; control transformers can skew readings and/or show as a fault. Nothing worse than telling a customer they have a dead short when in fact it is a tenant sub meter.
5. Meggers can be utilized on 
Transformers - Primary to secondary, primary to ground and secondary to ground (assuming any grounded conductor has the connection to ground isolated).
Motors - line to ground (with transformers and motors phase to phase connections should read as a dead short) There are additional test used on motors and transformers this megger test mentioned here are basic go no go field test. 
Circuit breakers disconnects, motor starters - with the load disconnected, pole to pole line, pole to pole load, line to load (CB open).
Feeders to include busway - Phase to phase, phase to neutral phase and phase and neutral to ground.
Switchboards, panel boards, MCC’s ECT - Phase to phase, phase to neutral phase and phase and neutral to ground.
Branch circuits – Phase to Phase, phase to ground and the often overlooked, neutral/grounded conductor to ground. 
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There are test standards and specifications available for all megger test to be performed, these include NETA, NEMA.
http://www.netaworld.org/
http://www.nema.org/
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There are also some basic “rules of thumb”, for go no go testing also commonly referred to as spot reading and generally the most common test most electricians will perform..
If the distribution equipment in question has gotten wet, experienced a fault that results in carbon deposits IT IS IMPERATIVE a company that specializes in this type of problem be contacted. In the way to many cases (one was too many) of injury and death I have been involved in, water and previous faults were the number one and number two causes of injury/death.
This test applies to conductors that are existing. Obviously we would like a full scale reading (infinity) which depending on the megger can be 1000 megohms, 2000 megohms, 4000 megohms or some meggers have higher megohm readings. One thing to remember about infinity FULL SCALE readings, Infinity on you meter can be beat by another meter this all depends on the full scale of the megger in use and the test voltage.
It is possible to damage equipment with a megger if you apply too high a test voltage, so it is imperative you know what you are testing and what is connected to what you are testing.
Typically I like to see high readings 50 megohms or higher, additionally if the readings phase to ground are A-phase 1000 megohms, B-phase 75 megohms, C-phase 1000 megohms, there may be something happening with the B-phase and while an acceptable reading this may warrant investigation.
I hesitate to say that there are cases where I have had reading below 50 megohms where the distribution equipment was re-energized with mitigating circumstances. BUT in all cases the readings were above 5 megohms and the customer was made aware of the situation and signed off on the re-energizing. A good example of this would be underground feeders and/or branch circuits.
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So you have a megger, you have read the instruction manual, you read AECM and Megger links below now you are ready to test something.
Set the megger to the lowest voltage scale and insert the test leads. Put you gloves on (rubber and leathers), hold the test leads apart and push the test button, the meter should go to full scale (air in most cases is a good insulator), that is an excellent reading. Next touch the leads together and push the test button this is a dead short the megger should read “0”. Now get some paper and a no. 2 pencil and scribble lines two large patches for your test clamps and numerous interconnecting lines. Using different voltage settings hit the test button, the meter may give an infinity reading or some reading in between, or it paper and lines may arc and spark till the paper either catches fire or clears the “FAULT”. With different paper thickness varying the scribbles and changing the test voltage you should be able to get an idea of your meggers reading.
Another test that for some reason always amazes some electricians is to connect your multimeter to the test leads (assuming you multimeter can handle the applied voltages) of the megger and push the test button to check the test voltage. Normally the megger output is a few volts above the published test voltage, i.e. 1000 VDC on the megger results in 1052 VDC on the multimeter.
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What megger should you buy?

In my opinion there are 3 basic meggers I would consider

All should have test variable voltages up to 1000 VDC, be digital with analog scale, 2000 megohms or more full scale readings. And just my experience buy a Fluke, AVO Biddle Megger, or AEMC brand. Additionally I would recommend calibration of you megger, multimerter and amp clamp at least every few years (we cal all our equipment yearly). Figure on spending between 300.00-700.00 dollars. Obviously the better meters with options to include multiple test voltages are going to cost you... Get a good case and hopefully treat it like you do your multimeter (which is like you life depends on it, because it does).At a minimum select an insulation resistance tester, with 250, 500, 1,000 VDC ranges a tester with 100 VDC would be included in any megger I purchase. 
Fluke and AEMC do not mention the Trade name Megger [I think] they list these testers as insulation resistance testers Megohmmeters.
AEMC 
http://www.aemc.com/techinfo/Charts/Megohmmeter/Megohmmeter_Comparison_Chart.pdf
Megger
http://www.biddlemegger.com/cgi-bin...nbeyemiw121002645030&command=link--bi2820.htm
Fluke
http://us.fluke.com/usen/products/categoryinsul.htm
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The best way to familiarize yourself is to test everything and document your results (for many reasons) and test often. Play with the tester. If the results seem questionable, question yourself, your test procedures, check the megger, leads apart then leads shorted.

Additional reading:

AEMC
http://www.aemc.com/techinfo/techworkbooks/megohmmeters/tech_megohm.pdf

Megger
http://www.omnicontrols.com/articles/Megger-A_Stich_in_Time.pdf

Fluke 
http://support.fluke.com/find-sales/Download/Asset/1579160_6115_ENG_C_W.PDF

Additional reading
http://www.hipot.com/faqs/insulation.shtml
http://ecmweb.com/mag/electric_testing_insulation_save/index.html
http://www.sefelec.com/en/insulation-resistance-test.php
http://bg.ecmweb.com/ar/electric_insulation_testing/index.htm


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## eddy current

Wow that was a long answer! Sorry bad, i didn't read it, only skimmed it. ;-)

To the OP......I would just ohm ressi circuits with a plain old ohm meter for shorts and grounds.
I would also check neutral to ground continuity for arc fault circuits. Before terminating the wires in the panel.


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## pete87

Badelectrician ... Wow . That is some info .


I have never meged anything ressi ... and as far as getting ready for AFCI ,

I would use a continuity tester to show if grounded .

If there was a outdoor circuit in question / problems ... I just run a new one .



Pete


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## ampman

eddy current said:


> Wow that was a long answer! Sorry bad, i didn't read it, only skimmed it. ;-)
> 
> To the OP......I would just ohm ressi circuits with a plain old ohm meter for shorts and grounds.
> I would also check neutral to ground continuity for arc fault circuits. Before terminating the wires in the panel.


If you didn't read that its your loss


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## eddy current

ampman said:


> If you didn't read that its your loss


? What do u mean by that?
How do u know I don't have extensive experience using metering tools like meggers? What have I lost exactly?

Not saying Bad's post wasn't very informative. Just commenting on it's length was all.

Keep in mind the OP asked for help in "dumbing down" how to use a megger. LOL


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## CADPoint

Thanks Brian!

Made a copy to a text editor for later reading and studying!


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## wadeco

just afci and gfci on one beaker and be done with it


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## wadeco

just afci and gfci on one beaker and be done with it


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## chicken steve

A stitch in time

~CS~


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## sbrn33

Thirty years and I have seen the need to Meg resi jobs maybe twice. Problems can almost always be tracked down.


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## The_Modifier

chicken steve said:


> A stitch in time
> 
> ~CS~


On of my favourite reads to brush up on testing. :thumbup:


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## macmikeman

480sparky said:


> I use a Fluke 1587. I megger as the last step in rough-in, then first step during trim.


So, how many months does each one of those steps take......


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## 480sparky

macmikeman said:


> So, how many months does each one of those steps take......


About 1/975th.


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## sbrn33

chicken steve said:


> A stitch in time
> 
> ~CS~


I have read this thing many times. I still wonder what it has to do with anything residential.


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## Meadow

MTW said:


> Yes, primarily because you look down your nose at American wiring methods.
> 
> As was stated on the other forum, how you would feel if an American electrician came onto a British forum and began criticizing your methods? I can assure you he wouldn't be tolerated for very long, particularly since you believe your methods are the most superior in the world.
> 
> Likewise, we don't take too kindly to having our methods criticized as being inferior.



Its not about looking down upon American wiring, its about improving what we have. If someone else comes up with something that can make this country better, why not copy it? 



> how you would feel if an American electrician came onto a British forum and began criticizing your methods? I can assure you he wouldn't be tolerated for very long


How do you know? Can you give me proof?


Ive been on UK, French and other foreign forums and I have criticized their their weak points. Just recently I was on a UK forum criticizing one of their earthing systems. Members listened and we discussed the theory behind my opinions rather then just plainly condemning it.


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## Tony S

MTW said:


> Yes, primarily because you look down your nose at American wiring methods.
> 
> As was stated on the other forum, how you would feel if an American electrician came onto a British forum and began criticizing your methods? I can assure you he wouldn't be tolerated for very long, particularly since you believe your methods are the most superior in the world.
> 
> Likewise, we don't take too kindly to having our methods criticized as being inferior.


 

You can believe this or not, we have several members from the US who have been made more than welcome.

They ask questions and they get questioned in return. If there’s any animosity to them I deal with it as Global Moderator.


As far as I know electrical safety concerns are universal.


I’m based in the UK but worked for a French company. Our equipment came from all over the world.

I don’t belittle any countries systems, but I will make comparisons. Given the choice I’d go for German systems.

I have the regulations/codes for the UK, NEC 2008/2011/2014, Canada, India, South Africa, Singapore, France, Germany and Benelux.


You’ve had a go at me before and as I said then “you don’t know me”


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## Tony S

End of subject as far as I’m concerned. You’ve had all the testing information this forum is getting out of me!


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## Meadow

Tony, Id be interested in your Ohm value equations. You can PM them to me if you like. Im willing to learn.




> Given the choice I’d go for German systems.


I will start researching German standards immediately :thumbsup:


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## Chris1971

Tony S said:


> You’ve had a go at me before and as I said then “you don’t know me”


Thank you for sharing your view points on this forum. You are welcome to post anytime. I appreciate your perspective.


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## MTW

Tony S said:


> You can believe this or not, we have several members from the US who have been made more than welcome.
> 
> They ask questions and they get questioned in return. If there’s any animosity to them I deal with it as Global Moderator.
> 
> 
> As far as I know electrical safety concerns are universal.
> 
> 
> I’m based in the UK but worked for a French company. Our equipment came from all over the world.
> 
> I don’t belittle any countries systems, but I will make comparisons. Given the choice I’d go for German systems.
> 
> I have the regulations/codes for the UK, NEC 2008/2011/2014, Canada, India, South Africa, Singapore, France, Germany and Benelux.
> 
> 
> You’ve had a go at me before and as I said then “you don’t know me”


I know what you've posted on these forums, and that's enough for me to make my determination. I stand by what I said.


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## MTW

meadow said:


> Its not about looking down upon American wiring, its about improving what we have. If someone else comes up with something that can make this country better, why not copy it?


Because our system is fine, and it doesn't need improving. It's people with your mindset (that we need to improve our system) that gave us the AFCI. 




> How do you know? Can you give me proof?
> 
> 
> Ive been on UK, French and other foreign forums and I have criticized their their weak points. Just recently I was on a UK forum criticizing one of their earthing systems. Members listened and we discussed the theory behind my opinions rather then just plainly condemning it.


I don't spend time of foreign forums, nor do I care to. I know that the Brits think they are the best in the world (think of Formula 1 racing) and I know they look down on everything non-British, whether they will admit it or not. Oh, and by the way, they are more than welcome to that national pride. I'm not downing, just saying it for what it is.


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## MTW

Chris1971 said:


> Thank you for sharing your view points on this forum. You are welcome to post anytime. I appreciate your perspective.


Don't mind Chris, he is the resident troll that likes to follow me around and put forth an opposing viewpoint to mine, simply because I'm the one posting it.


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## Meadow

MTW said:


> Because our system is fine, and it doesn't need improving. It's people with your mindset that we need improving is what got us the AFCI.


For the most part. It still lacks verification. 




> I don't spend time of foreign forums, nor do I care to. I know that the Brits think they are the best in the world (think of Formula 1 racing) and I know they look down on everything non-British, whether they will admit it or not. Oh, and by the way, they are more than welcome to that national pride. I'm not downing, just saying it for what it is.


The British system is based on the IEC and visa versa. The IEC is used in almost every country on earth outside North America. Testing of all new and remolded installations is mandatory. Its a basic skill taught to every apprentice being considered a vital part of fulfilling code requirements. 

In fact there is even a province in Canada (I believe it's in 99cents's territory) where the AHJ requires megger testing of new wiring despite being on an NEC based code. 


Anyway, its not just the British: 

http://www.legrand.com/files/fck/File/pdf/Guide-International.pdf


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## MTW

meadow said:


> For the most part. It still lacks verification.


And it should lack verification. For all your talk about being against the NEC and corruption of AFCI's, you want even more regulation over wiring systems. How do you think that's going to work out when the NEC is bought and sold by manufacturers? Please at least attempt to be consistent on this.






> The British system is based on the IEC and visa versa. The IEC is used in almost every country on earth outside North America. Testing of all new and remolded installations is mandatory. Its a basic skill taught to every apprentice being considered a vital part to fulfilling code requirements.
> 
> In fact their is even a province in Canada (I believe it's in 99cents's territory) where the AHJ requires meggering testing of new wiring despite being on NEC based code.
> 
> 
> Anyway, its not just the British:
> 
> http://www.legrand.com/files/fck/File/pdf/Guide-International.pdf


Again, I couldn't possibly care less what the rest of the world does, or doesn't do. If you want to test, fine. You're more than welcome to do all the testing you want. It's certainly your choice and if it makes you feel better, then do it. But please don't impose that on the rest of us who don't believe it's necessary.


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## MTW

meadow said:


> Its not about looking down upon American wiring, its about improving what we have. If someone else comes up with something that can make this country better, why not copy it?


OK, then please make a complete list of all the things you think are wrong with American wiring systems, and your proposed solution. You can leave out the obvious AFCI, and outside distribution (MGN's.)


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## Meadow

MTW said:


> And it should lack verification. For all your talk about being against the NEC and corruption of AFCI's, you want even more regulation over wiring systems. How do you think that's going to work out when the NEC is bought and sold by manufacturers? Please at least attempt to be consistent on this.


Regulation that actually does its job. Testing is cheap; AFCIs, GFCIs, over sized wires, labeling, certain wiring methods, ect ect is not. 





> Again, I couldn't possibly care less what the rest of the world does, or doesn't do. If you want to test, fine. You're more than welcome to do all the testing you want. It's certainly your choice and if it makes you feel better, then do it. But please don't impose that on the rest of us who don't believe it's necessary.



Right their you are condemning something that might actually work. I am not and willing to research everything through good, bad and ugly. 

To this moment you haven't answered my original question. How do you know any new installation complies with the NEC?


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## Meadow

MTW said:


> OK, then please make a complete list of all the things you think are wrong with American wiring systems, and your proposed solution. You can leave out the obvious AFCI, and outside distribution (MGN's.)



Ill start with our one size fits all oversized article 310.15.

Article 250, 240 taps rule, ect, ect latter.


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## MTW

meadow said:


> Regulation that actually does its job. Testing is cheap; AFCIs, GFCIs, over sized wires, labeling, certain wiring methods, ect ect is not.
> 
> 
> 
> 
> 
> 
> Right their you are condemning something that might actually work. I am not and willing to research everything through good, bad and ugly.


We will simply have to agree to disagree. We will never see eye-to-eye on this issue. 





> To this moment you haven't answered my original question. How do you know any new installation complies with the NEC?


If it doesn't trip the breaker and everything works, then it complies as far as I'm concerned.


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## Meadow

MTW said:


> If it doesn't trip the breaker and everything works, then it complies as far as I'm concerned.




What Im getting is that you would rather leave to job site with code violations then take pride in your work. Its that lack of pride where the NEC has to build safety factors into everything where we then gripe about needing to put more effort and cost into something as simple pulling wire.


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## MTW

meadow said:


> What Im getting is that you would rather leave to job site with code violations then take pride in your work. Its that lack of pride where the NEC has to build safety factors into everything where we then gripe about needing to put more effort and cost into something as simple pulling wire.


Now you're just being insulting. if you want to go down that road, you're more than welcome to, but please don't speak for my work.


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## Meadow

MTW said:


> Now you're just being insulting. if you want to go down that road, you're more than welcome to, but please don't speak for my work.



Dont look at this at face value or personally. Thats what you know who taught you. View it like this: even the best electricians can make a mistake. I made up a splice once only to have a GFCI trip. After investigating a single strand had come out from under the wire nut touching the metal box. Purely an accident that I would never have guessed was possible.


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## MTW

meadow said:


> Dont look at this at face value or personally. Thats what you know who taught you. View it like this: even the best electricians can make a mistake. I made up a splice once only to have a GFCI trip. After investigating a single strand had come out from under the wire nut touching the metal box. Purely an accident that I would never have guessed was possible.


So like I said before, test your work as much as you want. But don't insult, belittle or look down on those that don't. It's that simple.


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## ponyboy

meadow said:


> What Im getting is that you would rather leave to job site with code violations then take pride in your work. Its that lack of pride where the NEC has to build safety factors into everything where we then gripe about needing to put more effort and cost into something as simple pulling wire.



That's a huge stretch. You're basically inferring anyone who doesn't Meg a job before leaving it is looking the other way and ignoring 110.7. That's quite a reach. It's actually pretty ridiculous


Sent from my iPhone using Tapatalk


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## MTW

meadow said:


> Ill start with our one size fits all oversized article 310.15.
> 
> Article 250, 240 taps rule, ect, ect latter.


That's awfully vague.


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## Chris1971

MTW said:


> Don't mind Chris, he is the resident troll that likes to follow me around and put forth an opposing viewpoint to mine, simply because I'm the one posting it.


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## Meadow

ponyboy said:


> That's a huge stretch. You're basically inferring anyone who doesn't Meg a job before leaving it is looking the other way and ignoring 110.7. That's quite a reach. It's actually pretty ridiculous
> 
> 
> Sent from my iPhone using Tapatalk



Because you dont know just how many installations will actually pass or fail. When AFCIs came out the 30ma GFP proved otherwise, half the trips where from wiring errors. It was here that for the first time people broke meggers out.


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## Meadow

MTW said:


> That's awfully vague.



Haven't explained yet. 

Under BS7671 and the IEC wire sizing is based entirely on condition of use, or more precisely its ability to dissipate heat while still having a 5:1 safety factor. For example 2.5mm2 wire (close to our 2.08mm2 14 gauge) has a current rating anywhere from 27amps (clipped to a stud without insulation) to 12 amps (embedded within insulation). There is no one size fits all or 240.4 (D). Where we have to run 4/0 IEC countries can pull #2. Commercial installations rarely being in contact with thermal installation would benefit greatly. 

Most fixed loads do not require overload protection. A 17 amp heater can be wired with cable having a 17amp current rating however the breaker can be rated 32 amps. If an unskilled handyman or DIY installs a larger heater burning down the building he will be the one charged with manslaughter. Protecting unskilled labor is not a concern. 

There is no 80% or 125% rule either. Wire and breakers are all rated to 100%.

Where we have to pull 8 gauge wire for X load others others can pull 16 gauge for the same voltage and current. Where we are pulling 500MCM for motors other countries are pull #4. 

Voltage drop is done there after, with 3% of lighting and 5% for other uses when fed from a utility source.




And going by a one size fits all doesnt protect you when hitting extremes either (courtesy of almost always lurking):

http://www.resolvematters.ca/09/images/file/Cable_Ampacity.pdf




> A literature search revealed that this problem had already
> been addressed in the present edition of British Standard
> 7671:2008. An addition to this electrical code was issued in
> Regulation 523.7 which imposed an ampacity de-rating factor
> of 0.5 for any cable completely surrounded by thermal insula-
> tion. Applying the BS7671:2008 de-rating rule would have
> resulted in the incident cable installation being limited to 107.5
> A, just over half of the measured current flow in the cable.


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## Meadow

I will give you a real world example to the above. Take a typical 50 gallon 4500 watt water heater used the US. The unit is in the basement, cable stapled across a wooden beam. 4500/240=18.75amps. Under the NEC 240.4D limits be to #12 wire. Because the NEC calls this a continuous load I must up-size the wire as well with the breaker to 10 gauge. Thats 6mm2 for foreign folks. 

However under BS7671 knowing the wire is clipped direct I can select 1.5mm2 (16 gauge) NM cable with a 20amp breaker. If my wire is touching insulation 2.5mm2 (14 gauge) NM.

I then check for voltage drop. At 50 feet I get a 3.8672% voltage drop. If going 100 feet 2.5mm2 will suffice. 


So again, someone tell me whats wrong with comparing foreign standards? Could it be the NFPA doesn't want you to know something?


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## MTW

So on the one hand you want us to test everything, on the other you say we should start using #16 wire on water heaters. Sorry, that's just nonsensical talk with no basis in reality for our wiring systems. Let the British and Europeans have their systems and we have ours. They're not going to change and neither are we. This discussion is pointless.


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## Meadow

MTW said:


> So on the one hand you want us to test everything, on the other you say we should start using #16 wire on water heaters. Sorry, that's just nonsensical talk with no basis in reality for our wiring systems. Let the British and Europeans have their systems and we have ours. They're not going to change and neither are we. This discussion is pointless.





:laughing: 

You wanted something to back up my claims and I gave it to you. And its not like North America isnt listening. Canada is catching on, the ampacity tables are getting lax each cycle. I gave you a few examples a few months ago. My point is its not like we cant learn something and benefit. 


As for testing I bring that up because its worth looking into IMO. If testing can catch defects ahead of time why not? Personally if I had my way code would require meggering before energizing large switchgear. The arc blast isnt something to take lightly.


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## EM1

I don't do any residential work so I can't really speak on pro's or con's of pre-energizing megger tests on house services. However with the possible costs and liabilty of turning on any main service panel without at least a megger test seems foolish to me. A household branch circuit that is shorted or grounded is usually an inconvenience that will more than likely trip a 20 amp breaker. A short or ground on a main panel or 480V or higher branch circuit can be much more destructive. That can usually be caught by a 1 minute meg test. It all comes down to available fault current. 
When I started at the Power Co. many years ago, a wise oldster told me "Don't wory, if there is a fault it will trip somewhere...eventually".


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## JBrzoz00

Thanks for all the info guys !


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## eddy current

Curious 

So for the guys who are megging residential branch circuits, what voltage setting are you using on the megger?


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## 480sparky

eddy current said:


> Curious
> 
> So for the guys who are megging residential branch circuits, what voltage setting are you using on the megger?



1000v for me.


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## MTW

meadow said:


> :laughing:
> 
> You wanted something to back up my claims and I gave it to you. And its not like North America isnt listening. Canada is catching on, the ampacity tables are getting lax each cycle. I gave you a few examples a few months ago. My point is its not like we cant learn something and benefit.


And if you think #16 wire to serve 4,500 watt loads will ever see the light of day here, you are nuts. 




> As for testing I bring that up because its worth looking into IMO. If testing can catch defects ahead of time why not? Personally if I had my way code would require meggering before energizing large switchgear. The arc blast isnt something to take lightly.


I am repeating myself here....if you want to test, there is nothing stopping you. The NEC has never considered it a big enough issue to mandate it. Often, megger testing is done on large feeders and services before energizing. I worked for a company that megged every large pull we did. But you're talking about testing every circuit in a dwelling unit and that is unnecessary.


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## garfield

Bad electrician I have a couple 1000 volt meggers and recently came across a motor that megged good at 1000 volts but the vfd mfg said I need at least 2000 volts to approach the sensitivity of the vfd. What model would you reccomend. It looks like they jump from 1000 to 5000 volts. I would use it a couple times a year.


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## Meadow

MTW said:


> And if you think #16 wire to serve 4,500 watt loads will ever see the light of day here, you are nuts.


You never know, look what happened to 14 and 12 gauge NM in Canada. If enough people speak up that might change here too. Why do you think Im so vocal about AFCIs? Knowledge it power. A misinformed public can be talked into believing anything, and educated public can not. Im all for breaking conformity and letting people decide for themselves. 



> I am repeating myself here....if you want to test, there is nothing stopping you. The NEC has never considered it a big enough issue to mandate it. Often, megger testing is done on large feeders and services before energizing. I worked for a company that megged every large pull we did. But you're talking about testing every circuit in a dwelling unit and that is unnecessary.


And I think your company did the right thing. The arc blast/ arc flash on large equipment makes the investment worth it.

At the dwelling unit level while the risk is far less, however the concept should still be investigated further. If we megged in theory we wouldn't need AFCIs or GFP.


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## Bad Electrician

garfield said:


> Bad electrician I have a couple 1000 volt meggers and recently came across a motor that megged good at 1000 volts but the vfd mfg said I need at least 2000 volts to approach the sensitivity of the vfd. What model would you reccomend. It looks like they jump from 1000 to 5000 volts. I would use it a couple times a year.


What voltage is the motor?

I have never heard this but will ook into it.


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## eddy current

480sparky said:


> 1000v for me.


At what point does the wire actually get damaged from the megger? Ressi wire is only rated for 300 volts, no? 
I always assumed you shouldn't exceed the rating of the wire.....not for long anyway ;-)


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## RIVETER

eddy current said:


> At what point does the wire actually get damaged from the megger? Ressi wire is only rated for 300 volts, no?
> I always assumed you shouldn't exceed the rating of the wire.....not for long anyway ;-)


600volts.


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## 480sparky

eddy current said:


> At what point does the wire actually get damaged from the megger? Ressi wire is only rated for 300 volts, no?
> I always assumed you shouldn't exceed the rating of the wire.....not for long anyway ;-)


My rope is marked 600v.

I test at 500v for 1 min. If it holds at maximum ohms on the meter, I'll go to 1000v for 30 sec.


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## RIVETER

480sparky said:


> My rope is marked 600v.
> 
> I test at 500v for 1 min. If it holds at maximum ohms on the meter, I'll go to 1000v for 30 sec.


Is that INDUSTRY standard...or rule of YOUR thumb?


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## 480sparky

RIVETER said:


> Is that INDUSTRY standard...or rule of YOUR thumb?


My thumb.


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## RIVETER

480sparky said:


> My thumb.


I like your honesty.:thumbsup:


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## eddy current

RIVETER said:


> 600volts.


Interesting. Ressi wire (romex or NMD90) is only rated for 300 volts up here in Canada.


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## macmikeman

480sparky said:


> My rope is marked 600v.
> 
> I test at 500v for 1 min. If it holds at maximum ohms on the meter, I'll go to 1000v for 30 sec.


Now we are getting somewhere. So by your factoring, lets say 30 circuits, you will spend 1.5 hours at rough and another 1.5 hours at trim meg testing, correct?


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## 480sparky

macmikeman said:


> Now we are getting somewhere. So by your factoring, lets say 30 circuits, you will spend 1.5 hours at rough and another 1.5 hours at trim meg testing, correct?


No. Megging at rough is about 10 minutes. Megging at trim is about 2 minutes.


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## macmikeman

480sparky said:


> No. Megging at rough is about 10 minutes. Megging at trim is about 2 minutes.


At one minute at 1,000 volts and 30 seconds of 500 volts that would be something like 7 conductors then. Small panels out there in Cornpatch.


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## 480sparky

macmikeman said:


> At one minute at 1,000 volts and 30 seconds of 500 volts that would be something like 7 conductors then. Small panels out there in Cornpatch.



News flash: You don't need to meg circuits one at time. :whistling2:


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## triden

garfield said:


> Bad electrician I have a couple 1000 volt meggers and recently came across a motor that megged good at 1000 volts but the vfd mfg said I need at least 2000 volts to approach the sensitivity of the vfd. What model would you reccomend. It looks like they jump from 1000 to 5000 volts. I would use it a couple times a year.


It's true. A 480vac VFD has line transients that reach about 1000 vac peak, while a 600vac VFD can have line voltage peaks of 2000vac (dependent on cable length).

That's why it's important to use VFD rated cable with a high insulation breakdown resistance to prevent corona and arcing in the cable. As a result of all this, meggering an inverter rated motor will need much higher voltages to adequately test the insulation.


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## Bad Electrician

Insulation resistance testing has been shown by years and years of in the field use to minimize equipment damage. To test a system takes minimal time and I do not see where this is a issue with electricians that want to perform top quality work.

This is not, IMO an ground up ground down issue, it is a proven test method.


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## sbrn33

Bad Electrician said:


> Insulation resistance testing has been shown by years and years of in the field use to minimize equipment damage. To test a system takes minimal time and I do not see where this is a issue with electricians that want to perform top quality work.
> 
> This is not, IMO an ground up ground down issue, it is a proven test method.


Do you do new houses Brian?


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## Meadow

Bad Electrician said:


> Insulation resistance testing has been shown by years and years of in the field use to minimize equipment damage. To test a system takes minimal time and I do not see where this is a issue with electricians that want to perform top quality work.
> 
> This is not, IMO an ground up ground down issue, it is a proven test method.



I agree with you. Anyone wanting validation of a safe, code complaint system should megger test. Top quality work is what sets us apart from trunk slammers.


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## Bad Electrician

480sparky said:


> News flash: You don't need to meg circuits one at time. :whistling2:


And that is why you should do as you do, with the time factor.


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## Bad Electrician

sbrn33 said:


> Do you do new houses Brian?


Only for fire, lightning, floods and the like.


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## Meadow

480sparky said:


> News flash: You don't need to meg circuits one at time. :whistling2:




Finally someone gets it! :thumbsup:

I think the issue is people do not know the concepts all that well being discussed to start with.


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## 480sparky

meadow said:


> Finally someone gets it! :thumbsup:
> 
> I think the issue is people do not know the concepts all that well being discussed to start with.



Once I'm done mass-megging, I leave everything as is so when I come back to trim, it's all ready to mass-meg again. If it fails, then I start breaking the circuits down until I find the circuit(s) that have an issue.

I think it's more of an issue of, "I was never trained that way, and I didn't think of doing it that way. Ergo, I cannot do it and thus, by default, no one else can either."


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## chicken steve

480sparky said:


> Once I'm done mass-megging, I leave everything as is so when I come back to trim, it's all ready to mass-meg again. If it fails, then I start breaking the circuits down until I find the circuit(s) that have an issue.
> 
> I think it's more of an issue of, "I was never trained that way, and I didn't think of doing it that way. Ergo, I cannot do it and thus, by default, no one else can either."


So let's go thru the procedure for the nay sayers who've yet to deal with >>>>










First off, most afci manufacturers instructions state to disconnect any of their product from megging.....

(mother nature apparently having a pass) :whistling2:

Second, we want the MBJ & mains opened 

3rd, we want an all inclusive reading NtoG (try a big blue nut) :thumbup:

4th...if there is a problem....*(NEXT!)*

~CS~


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## 480sparky

chicken steve said:


> ........First off, most afci manufacturers instructions state to disconnect any of their product from megging............


When I'm done roughing in, there's no AFCI's on site, let alone in the panel. So that's a moot point.


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## Meadow

480sparky said:


> When I'm done roughing in, there's no AFCI's on site, let alone in the panel. So that's a moot point.



True, but you know they wont be tripping latter from wiring errors.


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## MTW

meadow said:


> You never know, look what happened to 14 and 12 gauge NM in Canada. If enough people speak up that might change here too. Why do you think Im so vocal about AFCIs? Knowledge it power. A misinformed public can be talked into believing anything, and educated public can not. Im all for breaking conformity and letting people decide for themselves.


I can assure you that we will never see #16 wire allowed to carry a 4,500 watt load, ever, under any circumstances.


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## MTW

meadow said:


> Where we have to pull 8 gauge wire for X load others others can pull 16 gauge for the same voltage and current. Where we are pulling 500MCM for motors other countries are pull #4.


This is a meaningless comparison. For starters, European and American cable types are completely different. But even then, unless they are using some exotic ultra high temperature insulation for motor conductors, there is no way what you're saying is even remotely true. 500 MCM vs. #4? Yeah, ok. :no::no:


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## Meadow

MTW said:


> I can assure you that we will never see #16 wire allowed to carry a 4,500 watt load, ever, under any circumstances.



With our NFPA you might be right. But unless you dont fight for something it will never change.


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## Meadow

MTW said:


> This is a meaningless comparison. For starters, European and American cable types are completely different. But even then, unless they are using some exotic ultra high temperature insulation for motor conductors, there is no way what you're saying is even remotely true. 500 MCM vs. #4? Yeah, ok. :no::no:



Can you tell me how they are different? I know how and why, the question is do you?


Keep in mind our ampacity tables are based on worst case scenario (embedded within thermal insulation) where heat dissipation is zero. In open air that changes, and the IEC recolonizes that letting you take advantage of it.

I also take it you have never used this equation in our NEC:


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