# So I bought a megger...



## BryanMD (Dec 31, 2007)

before anyone else gets to jump in.. RTFM! 

that's a current model.
did it not come with a manual?


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## nrp3 (Jan 24, 2009)

It didn't. The users guide I think is on cd. I know, thats what I get for buying used. It is available online and I have looked at it, however it is more about features and less about interpreting the readings. I am new to using a megger. I bought it to figure out these sorts of problems. I have the megger supplement about using meggers. Most of the pamphlet is about testing motor and transformer windings. I bought this unit because it seemed to be able to do everything I wanted. I may not be using it correctly either. Hoping those with experience will shed some light.


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## 480sparky (Sep 20, 2007)

Uh, I don't think you're supposed to have the AC power on when you megger a conductor.

Users' Guide.

Safety warning # 1 from that very guide:



> The circuit under test must be switched off, de-energised, securely isolated and​
> proved dead *before *test connections are made when carrying out insulation and
> 
> continuity tests.​


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## BryanMD (Dec 31, 2007)

480sparky said:


> Uh, I don't think you're supposed to have the AC power on when you megger a conductor.


there goes Ken... actually reading through the post again.


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## nrp3 (Jan 24, 2009)

Ok, I'm a little slow, what did I miss?


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## RIVETER (Sep 26, 2009)

*Megger*

I agree with 480sparky...Put that in your megger and crank it. Seriously, though, I may have not been fully utilizing the meggers that I have used, but all I have ever looked for is very, very close to infinity.

RIVETER


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## JohnJ0906 (Jan 22, 2007)

nrp3 said:


> Ok, I'm a little slow, what did I miss?


Turn off AC power.
Remove all lamps from light fixtures, unplug everything.
Remove GFCIs, Dimmers, or any other such device, and wirenut them through.
Your megger probably has a battery voltage setting - Mine has a 200Kohm setting at battery voltage, before the 250vDC, 500vDCand 1000vDC settings. *Use it first. *That way you can find out if you have removed all the above items without frying them.


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## BryanMD (Dec 31, 2007)

nrp3 said:


> Ok, I'm a little slow, what did I miss?





nrp3 said:


> I seperated out the two runs of poles. I got a reading of .1 meg and 10 volts applied and the other was .2 meg *with 120v applied*... I removed some romex from the attic that went nowhere *but was live*.



your assignment nrp, is to compare and contrast two common terms: voltage & continuity and apply same to the function of a megger.


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## Lone Crapshooter (Nov 8, 2008)

To use a megger the power must be off and every thing that is normaly connected to ground must be isolated from ground all line to neutral and line to line loads must be removed from the circuit. The only thing you want to test is the hot conductor. Then with all of the loads disconnected check the neutral conductor. If you just removed the hot wire and did not isolate the rest if the circuit you are reading to ground through loads . One of the main things about megging is isolating from ground then if it still reads to ground that is your problem. 
One thing you could do to check for isolation is check the circuit with a ohmmeter first then when reads several megs to ground then put the megger on the circuit. Working as a industrial electrician there is hardly a day goes by that I dont have to meg something. Most of the time it is a 480 0r 2400 volt motor and it and by their very design they are isolated from ground.Sometimes we will have to meg a switchrack and that is when the fun comes in trying to isolate everything from ground we may work for a hour or more trying to get everything off the bus so we can check for grounds.
Listen Think Solve
LC


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## nrp3 (Jan 24, 2009)

Those voltage applied readings I mentioned are what the megger was applying to the circuit at the time. That romex I removed from the attic was part of the same circuit in the garage. It went to something that was associated with some previous garage door openers. I tore everything apart and seperated the neutrals, grounds, black and red conductors on the sections of 12-3. The circuit was off and got readings if remember correctly 25 meg or off the scale at 276 applied volts (250 volt setting). All the sections I checked within the garage had similar readings. A portion of the home run was the only different one, lower, though I can't remember the exact figure.

The UF readings I took today were radically different, though it would make sense that different lengths of different insulation on a rainy cold day might be different.

I know there are degrees of continuity. This meter has a couple of settings. In the garage, there was a section of 12-3 that had a red conductor that was open that I replaced. The whole house was re sided with new wood clap boards and the nails they were using seemed a bit long...


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## nrp3 (Jan 24, 2009)

I gave up on the basement AFCI problem. It took less time to remove the wiring and replace it than to test it. I altered the garage wiring some so I will see what happens with that.


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## ampman (Apr 2, 2009)

go to meggers website and log in then download "a stitch in time" its a good read on using a megger


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## nrp3 (Jan 24, 2009)

I have the booklet version. I have read it through and still a little uncertain. I'd like to know what readings people get. That basement section I rewired still was tripping the breaker. All that was left was the four cfl bulbs and the breaker. I changed the bulbs and the breaker. Nothing left. Still would like to know what the problem was.

I took another stab at the garage today. The breaker trips after a period of time, like after I went to lunch. It tripped a couple of times while we were testing the new generator and transfer switch. The megger readings for today were 6-10 gig ohms on the 50 v setting and 20 g in the 500v range. There is a section that seems to be in the 650-700 meg range that I will check further tomorrow. The pamphlet that came with the CH GFI breaker mentions that a cause of tripping could be more than a 250 run one way in the wiring. This would qualify for that. 

The pole lights seem to be holding with the two sections isolated.


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## nolabama (Oct 3, 2007)

nrp3 said:


> The breaker trips after a period of time, like after I went to lunch.


thermal
just read your OP 
prolly not thermal but could be


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## nrp3 (Jan 24, 2009)

I checked the current with the clamp on. I had three 4 bulb t-8 strips, six cfl floods, a 500w work light, and three garage door openers plugged in. It came to 6.63 amps. I couldn't force it to trip. I moved the work light around to different receptacles, tried moving some of the three and 4 ways, and couldn't get anything to happen. It must have taken at least an hour for it to trip and it happened while I was out. The only time I saw it trip was when the transfer switch went from utility to gen power and back.


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## ElectricBill (Aug 14, 2009)

I assume you have tried a new GFCI breaker for the garage? Well worth a shot if you haven't.


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## nrp3 (Jan 24, 2009)

I have another new breaker to try. It made it a week or so without tripping. I'll meg some more tomorrow. I am trying to not change to many things at once, but you are right, its worth a shot. The one section that seems to have a lower reading is in the same area that I already replaced a section of 12-3 romex. That one was obvious though, no continuity, the switch wouldn't work.


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