# Testing wiring with a megger



## Angel Advanced Tech

Are there any resources for testing wiring with a megger? An example is to test wiring in a home which reads clear in terms of continuity but trips an arc fault under load. Another example is to certify that a wire is in safe working condition unquestionably. I'm currently using the Fluke 1507. Also I need a document template showing a cables funtionality or disfuntion. to validate the need to use this tool I have called 3 different Engineers but the contractor I'm working with says he has never heard of anyone using this method. He says usually his other electricians test for continuity between wires. I'm not comfortable with this.. There really is no garuantee that under load the insulation is in tact enough to prevent a ground fault ect. Any experience with this matter is a good thing, please share...


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## dronai

Residential, I used a continuity tester for many years with no problems. A meggar will show a ground fault that sometimes the continuity test wont" show. Last time I founds a problem with an AC condenser control wires shorted the board in the air handler, but showed no continuity with a regular meter. 

600V insulation test I use to give it 1000V, but a testing company at a plant told me not to exceed the insulation rating ? There are some old threads here with your answers


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## scotch

Angel Advanced Tech said:


> Are there any resources for testing wiring with a megger? An example is to test wiring in a home which reads clear in terms of continuity but trips an arc fault under load. Another example is to certify that a wire is in safe working condition unquestionably. I'm currently using the Fluke 1507. Also I need a document template showing a cables funtionality or disfuntion. to validate the need to use this tool I have called 3 different Engineers but the contractor I'm working with says he has never heard of anyone using this method. He says usually his other electricians test for continuity between wires. I'm not comfortable with this.. There really is no garuantee that under load the insulation is in tact enough to prevent a ground fault ect. Any experience with this matter is a good thing, please share...


Look at youtube for UK videos on doing this electrical testing....it's a requirement there.


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## MechanicalDVR

I've always tested new circuits before connecting them up and turning them on.

What don't you know how to do?


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## joebanana

I'd have to concur with the contractor, I've never heard of ringing out a residence with a megger either. Lets say you find a questionable circuit, what then? Re-run it? If it's residential, that could be a problem, unless everything is in conduit. Don't laugh, I've seen it done in Beverly Hills, Bell-Air, and Brentwood. Rigid no less. In the walls.
What if you have an AFCI that trips, but the cable meggers okay? If it only trips under load, that wouldn't indicate a bad cable.
But, hey, go for what you know.


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## MechanicalDVR

joebanana said:


> I'd have to concur with the contractor, I've never heard of ringing out a residence with a megger either. Lets say you find a questionable circuit, what then? Re-run it? If it's residential, that could be a problem, unless everything is in conduit. Don't laugh, I've seen it done in Beverly Hills, Bell-Air, and Brentwood. Rigid no less. In the walls.
> *What if you have an AFCI that trips, but the cable meggers okay?* If it only trips under load, that wouldn't indicate a bad cable.
> But, hey, go for what you know.


I kind of doubt that would happen.


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## sbrn33

MechanicalDVR said:


> I kind of doubt that would happen.


97% of the time it is a load not the wiring.


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## joebanana

MechanicalDVR said:


> I kind of doubt that would happen.


That was kinda my point. Bad makeup, defective device, failing refer motor, bad lamp cord, Chinese AFCI, bad 3-way lamp socket, etc. would be more likely than a bad cable section.


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## nrp3

The last remodel I did, the problem with the afci was the existing wiring, actually the light fixture. I don't know that the continuity test would have found it or not. The megger found the pinched wiring.


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## splatz

The OP has unwittingly stumbled on my favorite controversy  I'll give you the low down from a minority member, a fellow megger lover. 

I think it would be a good idea to megger wiring rather than just test for continuity prior to energizing, it will catch occasional odd faults that waste a great deal of time money and trouble, and it's not that big a deal in the big picture. 

Others feel like their current methods are completely fine and it's not worth the trouble for the few problems it would find. 

It's just a basic risk benefit decision. Nobody can produce anything like hard numerical data what the risks and benefits are, so what people actually do is just going to come down to personal preference. Reasonable people can disagree. 

For me, ideas like quality control and continuous improvement, doing things right the first time, taking pride in my work to the point of OCD about it - these make me agree with the OP it's a good practice.


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## HackWork

You should megger all the circuits in a house that was roughed in with staples. That's where the problem lies, over driven staples.

That's also why the pro's use duct tape, empty romex sheath, string, etc. to secure romex, no issues with AFCIs.


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## MTW

Where's Essex to tell us how it's done there? Oh wait, he's not an electrician.


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## MechanicalDVR

MTW said:


> Where's Essex to tell us how it's done there? Oh wait, he's not an electrician.


Have you not seen his anti megger posts????


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## Essex

In the UK we need to carry out a continuity test of the live and earth of each circuit with the live and earth connected together at the furthest point of the circuit. Clearly this is a dead test. 

This them proves you have continuity all the way to the end of the circuit and back again on the earth in the event of a fault. 

Then with no load on the circuit we have to put the insulation resistance tester across L-N, L-E and N-E on the circuit to be tested. Again clearly this is a dead test. 

The results should be what we call 'infinity'. Anything measurable indicates a fault on the circuit and it should be corrected prior to the circuit being energised. 


Sent from my iPhone using Tapatalk Pro


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## Essex

Sent from my iPhone using Tapatalk Pro


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## John Valdes

I never megged anything unless I had a problem with it.

In fact, I never saw or used a megger until I started working in manufacturing plants.

I do not own one now nor have I ever owned one. But everyone I worked for either had one or I asked for one.

I do see the merits of using a megger. Just never used one in residential wiring.


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## MechanicalDVR

John Valdes said:


> I never megged anything unless I had a problem with it.
> 
> In fact, I never saw or used a megger until I started working in manufacturing plants.
> 
> I do not own one now nor have I ever owned one. But everyone I worked for either had one or I asked for one.
> 
> I do see the merits of using a megger. Just never used one in residential wiring.


Megging cables and new circuitry was a standard spec on so many jobs I have been on and I have kept the practice going.

I own three meggers myself.


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## gnuuser

I megger all circuits resi or industrial ( for my own peace of mind)
and to verify the meter i also use a wanderer lead (short length of wire with a precision resistor)
and i often document the results for my own records.


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## Essex

gnuuser said:


> I megger all circuits resi or industrial ( for my own peace of mind)
> and to verify the meter i also use a wanderer lead (short length of wire with a precision resistor)
> and i often document the results for my own records.




To stay accredited over here we need to have our meters calibrate every twelve months and produce the certificates annually.


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## Essex

A screen shot from a new installation certificate.


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## mitch65

How many test your ground resistance when installing services?


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## gnuuser

mitch65 said:


> How many test your ground resistance when installing services?


I do! and laugh like hell when the worms fly up out of the soil(even more so when the apprentices start grabbing the worms for bait).


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## Switched

HackWork said:


> You should megger all the circuits in a house that was roughed in with staples. That's where the problem lies, over driven staples.
> 
> That's also why the pro's use duct tape, empty romex sheath, string, etc. to secure romex, no issues with AFCIs.


That's because staples are not approved for romeo Hax!!!!!!!!!!!!!!

Now, I think your methods are just a waste of materials, I simply wrap the wiring around the studs in a spiral like fashion.... Imagine the barber pole.....

:jester:


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## HackWork

Switched said:


> That's because staples are not approved for romeo Hax!!!!!!!!!!!!!!
> 
> Now, I think your methods are just a waste of materials, I simply wrap the wiring around the studs in a spiral like fashion.... Imagine the barber pole.....
> 
> :jester:


Believe it or not, my first reaction to that was that it was a great idea. Then I realized the drywall would smoosh it.


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## Moonshot180

those arc fault breakers can nuisance trip occasionally, don't necessary think that you have an end device and/or wiring problem.


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## OrionElectric

*megger checks*

I've used a 500V megger for 30 years, mostly on industrial jobs but also residential when some anomalous intermittent fault has been reported. I have gone to sites that reported lightening strikes which have sent surges through the house wiring. A megger is a great way to see if the damage is critical. Tools and tests are great, but an intelligent systematic approach- isolate, insulate, and terminate, have been my best guides.


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## manchestersparky

Switched said:


> That's because staples are not approved for romeo Hax!!!!!!!!!!!!!!
> 
> Now, I think your methods are just a waste of materials, I simply wrap the wiring around the studs in a spiral like fashion.... Imagine the barber pole.....
> 
> :jester:


Better yet drill holes up the stud every 18" to 24" and weave the NM through them ...................:whistling2:


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## telsa

I megger Big Box Line-ups and Feeders as a matter of routine.

You'd be amazed at the (metallic -- ie sockets ) junk that the boys leave in the Big Boxes.

They figure it's an "oopsies" and if they slink off, no-one will blame them for the boo-boo.

And that socket was so tough to get to, too.

So, I personally torque all of my Big Box connections, and then Megger the bugger.

I've also learned that you can't trust the crew to not damage feeders during pulls.

Not that it's happened to my fellas -- but I've heard enough stories.

The local PG&E meter 'maid' has seen so many 'blasts' that she won't enter the space during power-up. (!!!)

Less than two-months prior a foreman was sent to the hospital -- right before her eyes.

Yeah, he trusted his crew.

[ While a DMM can spot bolted shorts -- it can't spot marginal situations -- like too much dirt and dust on the busing. This stuff can become conducting with heat and amps. ( initiates a corona discharge (arc) which then does real damage. ) ]


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## Lone Crapshooter

Back many many years ago when we had the Rating Bureau along with real inspectors the inspector would disconnect all neutrals and grounds and ring each circuit line to neutral and line to ground. They were looking nails through the Romex and at that time BX.
They used a telephone magneto and a bell.
Now we have self employed inspectors and some in city inspectors some are outside of the city limits inspectors some just do services some do the entire job.
Being a industrial guy I am out of that mess but I do try to go to the inspectors meeting if they are talking about something that interests me but the residential guys dominate the IAEI here and that is fine with me.

LC


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## Zog

This is an excellent reference
http://www.biddlemegger.com/biddle/Stitch-new.pdf


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## power

Maybe I am the black sheep here....but I just turn the breaker ON when we've installed the upstream cables. 

If engineers want some "report" about our installations integrity, given them am ampacity reading upon energization to a no-load branch branch circuit. 

I have NEVER EVER heard about hi-pot (megger) testing building wiring.


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## Going_Commando

Resi? Turn it on and wait for the bang. If it don't go bang, then she's good!:thumbup:


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## splatz

power said:


> Maybe I am the black sheep here....but I just turn the breaker ON when we've installed the upstream cables.


Don't sweat it, you're not alone, no shortage of black sheep around here.


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## macmikeman

I test residential circuits before energizing them the following way: Step one, either meg test the feeders between my outdoor main breaker to my indoor load centers or test them with a wiggy one lead to the live side of the main breaker and the other lead touches the feeder on the load side of the main breaker in the off position. If it shakes and says 120 volts then it is damaged someplace. Now for the branch circuits- Make sure all branch breakers are off. Turn on outside main breaker and energize panel. Test with wiggy between one of the now energized line lugs to each load side of the breakers in the off position. AFCI breakers will show up as shorted , but it is the internal low resistance wiring of the afci so just skip them. Non afci circuits should not show 120 volts on testing. If they do show 120 volts , make sure no loads are plugged in and you are not reading across any filaments or other loads and try again. If still reading 120 volts between the hot lug and the dead side of a circuit breaker connected to a branch circuit, you have a short someplace in the wiring. 
Go look for likely places where one of the drugged up carpenter's shot thru a cable with a nail gun in a place where they shouldn't have driven a nail in the first place, like for instance the time one of the above mentioned idiots used a nail gun with 16 penny nails to hang a pre-fabbed door casing to the rough door frame studs and shot clean thru poking into my cables stapled down the center of the back side of the king stud. He hit right where the staple was holding the cable to the wood in the center of the stud. Bullseye. You don't need 16 penny nails to hang a pre hung door frame. He was too lazy to change to a smaller nail size, just used what was in the chamber. I found the offending nail using a volt tic.


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## power

@*macmikeman* - I can tell your experience is aggravating for you!! I too have seen carpenters riddle their millwork with small nails cuz of laziness. 

BTW = What is a "wiggly"?


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## telsa

joebanana said:


> I'd have to concur with the contractor, I've never heard of ringing out a residence with a megger either. Lets say you find a questionable circuit, what then? Re-run it? If it's residential, that could be a problem, unless everything is in conduit. Don't laugh, I've seen it done in Beverly Hills, Bell-Air, and Brentwood. Rigid no less. In the walls.
> What if you have an AFCI that trips, but the cable meggers okay? If it only trips under load, that wouldn't indicate a bad cable.
> But, hey, go for what you know.


Defective AFCI ?


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## gnuuser

power said:


> @*macmikeman* - I can tell your experience is aggravating for you!! I too have seen carpenters riddle their millwork with small nails cuz of laziness.
> 
> BTW = What is a "wiggly"?


wiggy on steroids


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## splatz

power said:


> @*macmikeman* - I can tell your experience is aggravating for you!! I too have seen carpenters riddle their millwork with small nails cuz of laziness.
> 
> BTW = What is a "wiggly"?





gnuuser said:


> wiggy on steroids


LOL 

A Wiggy / Wiggins was a solenoid type voltage tester made by I think Square D, they no longer make them but others do and the name survives, people call any solenoid type tester their Wiggy.


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## power

splatz said:


> LOL
> 
> A Wiggy / Wiggins was a solenoid type voltage tester made by I think Square D, they no longer make them but others do and the name survives, people call any solenoid type tester their Wiggy.


Ok, I see. Thanks So Much for your response. I used to have one of those.....I think it was made by IDEAL.


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## macmikeman

This damn apple laptop whatdocallit---- MacBook.... changes my spelling all the time even when I don't ask it to. I constantly change words back to what I put down but I missed that one. My "Wiggie" is a Knopp brand solenoid tester. And the machine just turned my wiggie into my biggie for me again....... Cripes , in this pc world you could go to jail for having your computer change your words to the wrong ones and offend some ****........


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## EB Electric

It is interesting to see the common practices in other parts of industry. Being in the medium voltage power systems side of things, megger testing is a daily thing, common tool. I could see for sure it not being common in residential as many have said. They are a very expensive piece of test equipment, so I could see many companies not wanting that cost for the very few times they might need one. In the medium voltage systems I think it comes down to safety and liability. There is just too large of consequences (physically and financially) for the companies and guys in the field if something goes wrong for them to not use the basic test equipment to asses the condition of the equipment. I simply would not energize new cable or any equipment, whether I did it myself or done by the most trustworthy contractor in the county, without some kind of test to tell me that insulation is decent and I am not energizing into a dead short. 

We had it just the other week where low voltage 600V underground service burnt up to a facility. Facilities electricians insisted the cable is fine just re-fuse and re-energize.... they checked it with a multimeter, read open loop phase to ground and phase to phase it has to be good.... Put on our 1kV megger and see dead short right away. They tried to debate and debate, eventually they pulled out their cable and it was waterlogged and insulation was very obviously bad to the naked eye at multiple places in the run of cable. To me that is proof in the value of having the proper test equipment for the job.


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## macmikeman

EB Electric said:


> It is interesting to see the common practices in other parts of industry. Being in the medium voltage power systems side of things, megger testing is a daily thing, common tool. I could see for sure it not being common in residential as many have said. They are a very expensive piece of test equipment, so I could see many companies not wanting that cost for the very few times they might need one. In the medium voltage systems I think it comes down to safety and liability. There is just too large of consequences (physically and financially) for the companies and guys in the field if something goes wrong for them to not use the basic test equipment to asses the condition of the equipment. I simply would not energize new cable or any equipment, whether I did it myself or done by the most trustworthy contractor in the county, without some kind of test to tell me that insulation is decent and I am not energizing into a dead short.
> 
> We had it just the other week where low voltage 600V underground service burnt up to a facility. Facilities electricians insisted the cable is fine just re-fuse and re-energize.... they checked it with a multimeter, read open loop phase to ground and phase to phase it has to be good.... Put on our 1kV megger and see dead short right away. They tried to debate and debate, eventually they pulled out their cable and it was waterlogged and insulation was very obviously bad to the naked eye at multiple places in the run of cable. To me that is proof in the value of having the proper test equipment for the job.


For 600 volts and below any cable run underground must be rated for wet locations and intrusion by water into the cable should not be automatically the reason to pull the cable out and replace it. I'm all for megging feeders, I have two of the testers , but seriously , did it have a real short or did it just get wet and your 1kv test find the water?


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## EB Electric

macmikeman said:


> For 600 volts and below any cable run underground must be rated for wet locations and intrusion by water into the cable should not be automatically the reason to pull the cable out and replace it. I'm all for megging feeders, I have two of the testers , but seriously , did it have a real short or did it just get wet and your 1kv test find the water?


The insulation was bubbled up off of the conductor in several places, and you could see areas where the insulation was burnt off completely in a few spots. The megger showed it as no resistance between phase to ground and also failed phase to phase... to me that is a real short circuit water or not.


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## nrp3

Wouldn't finding the water with megger mean its compromised anyway? Can't troubleshoot direct burial cables very well with a multimeter. If you get lucky and find enough of a fault great, but more often than not its not going to tell you what you need to know. Who was it though, talking about the old BX passing the test, but if you gave it a whack with a tool and suddenly the insulation moves enough, falls off and shorts out. Never thought of that.


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## telsa

macmikeman said:


> This damn apple laptop whatdocallit---- MacBook.... changes my spelling all the time even when I don't ask it to. I constantly change words back to what I put down but I missed that one. My "Wiggie" is a Knopp brand solenoid tester. And the machine just turned my wiggie into my biggie for me again....... Cripes , in this pc world you could go to jail for having your computer change your words to the wrong ones and offend some ****........


It's now a pandemic.

You see such glitches all over the Internet.

Now imagine that folly embedded as AI.


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## gnuuser

telsa said:


> It's now a pandemic.
> 
> You see such glitches all over the Internet.
> 
> Now imagine that folly embedded as AI.


I shudder at the thought just thinking about the sheer amount of hardware that will be required to create a sentient computer.

@macmikeman you should be able to turn spell check /auto correct off in preferences.


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## nownojin

Whats a good megger for the recently unemployed ?


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