How would you

[bikeindy]

I am wondering what step you would take to inspect a home after a lightning strike. In this case every electronic component in the home was blown even ones with surge protection.

 

[mdshunk]

Megger check. Use the search button. I think I posted a detailed step-by-step on this, related to lightning strikes, once upon a time.

 

[satcom]

I am wondering what step you would take to inspect a home after a lightning strike. In this case every electronic component in the home was blown even ones with surge protection.

Every strike is different, from little, or no damage, to cables blown apart like a spent firecracker. What did you find on your visual inspection, any indication of damage? A megger helps, in finding cables, with breakdown faults.

If you would like to see pictures of cable faults found on jobs, just PM me with your e-mail address.

 

[mdshunk]

This isn't the thread I was thinking about, but it's a start: http://forums.mikeholt.com/showthread.php?t=87564

Also, check the GEC connections over really well. I have found the worst damage in homes with very loose or disconnected GEC's to the rods and pipes.

 

[LarryFine]

Megger check. Use the search button.

But, my megger doesn't even have a search button. :-?


But then, my keyboard doesn't have an "any" key.

 

[jscottelwood]

Megger...Valid or not?

Megger...Valid or not?

My guys have asked me an interesting question. Why do we Megger pulled wires before termination and what does it prove? Well, I'm a firm believer in never stifling enthusiasm and I believe "showing" far exceeds "telling". I set up an experiment. Here goes...I took a piece of conduit 4 feet long. Inserted a #12 wire. connected the Megger to the wire and the conduit. Pushed the button and "viola", got an infinite reading. Then I pulled out the wire and made breaks in the insulation with my strippers and a sharp knife and reconnected the Megger. I fully expected the Megger (Fluke) to show bad insulation or a short or anything! What I got was a reading of infinite! How can this be? Does the hand held not have the power to throw an arch across 1/64th of an inch? Do I need to use the hand crank model? Or do Meggers not show breaks in insulation, only shorts? Any help would be appreciated.

 

[don_resqcapt19]

Then I pulled out the wire and made breaks in the insulation with my strippers and a sharp knife and reconnected the Megger. I fully expected the Megger (Fluke) to show bad insulation or a short or anything! What I got was a reading of infinite! How can this be?

Air is a good insulator and 500 or 1000 volts won't jump a very big gap. This is a point that I have made a number of times about a megger. It is a great tool but there are a number of cases, like this, where it can give you a false sense of confidence. Now if you had an installation like this, you could check it with a megger and think that there is no issue, however as soon as the conduit gets some moisture in it you will find out otherwise.
A couple of sources say that the dielectric stength of air is about 3kV per millimeter. (a millimeter is a little more than 1/32")
Don

 

[brian john]

Try this. megger a piece of notebook paper at 1000 VDC then scribble with a #2 pencil megger again.

Sorry guys posted before I KNOW. Click on the picture below.

 

[bikeindy]

meggered out the home today found two bad circuits, but it turned out good in the end the proble on both circuits was nicks in the insulation in the receptacle box. The nicks were caused by an electrician using a knife instead of stripers but that is for another thread.

 

[mdshunk]

The nicks were caused by an electrician using a knife instead of stripers but that is for another thread.

That's a "root cause" I've heard before, but I don't really like it when it is stated that way. The knick may have indeed been caused by a knife, but the use of the knife instead of strippers is not the cause. The improper use of the kinfe was the cause. I've used a knife to skin out cable jackets all my career, as many others have, and I don't have this problem.

 

[e57]

Strippers of the cable type can do just as much damage IMO....

Anyway - lighting stike on a house, I have never dealt with, but assume I might want to open walls for some of it. What got hit - where did it go - how did it get there? Then assume that path is done! but since everything in the building is toast - it sounds like all of it....

 

[cschmid]

good to see you tonight marc or should we atart calling you megger marc??So my megger is a fluke and it is an electric one not a crank which do you guys perferr and why??I have used both and I own the electric one because of cost but I think the crank is a better megger..no batteries to change..:grin:

 

[dereckbc]

I would think a meggar is inconclusive for a home using romex. One conductor could be burned, whike the mate is just fine. A meggar would not see that now would it?

Commercial or industrial I can see it having better results because the conductors are in conduit, then you test each conductor to ground. Then again i am just a train driver

 

[satcom]

I would think a meggar is inconclusive for a home using romex. One conductor could be burned, whike the mate is just fine. A meggar would not see that now would it?

Commercial or industrial I can see it having better results because the conductors are in conduit, then you test each conductor to ground. Then again i am just a train driver [/QUOTE

 

[mdshunk]

I would think a meggar is inconclusive for a home using romex. One conductor could be burned, whike the mate is just fine. A meggar would not see that now would it?

So what's your proposal? Condemn the house and tear it down? Do nothing, and pretend the house never suffered a lightning strike? Or maybe just do all you an with the best tools available for that chore, like a megger?

I'm not sure how one conductor could get "burned" anyhow without substantial damage to its insulation. Since the current carrying conductors either parallel to, or are wrapped radially about, the ground wire in a cable assembly, and there was a substantial fault in one current carrying conductor it would show up. If it doesn't show up, there is no real problem to talk about in the end. There may be some "damage" left unfound, but not to a degree that it would pose a hazard.

 

[mdshunk]

good to see you tonight marc or should we atart calling you megger marc??So my megger is a fluke and it is an electric one not a crank which do you guys perferr and why??I have used both and I own the electric one because of cost but I think the crank is a better megger..no batteries to change..:grin:

I think if a guy has anything at all, crank analog or battery digital, he's ahead of the curve.

 

[satcom]

I think if a guy has anything at all, crank analog or battery digital, he's ahead of the curve.

Yes, they are ahead of the curve, I prefer the crank.

Ok on meggers, and NM Cable, when your checking NM cable you will test each conductor in a closed circuit loop, example, white, to black, white to ground, black to ground, loop, white closed to balck, and ground. It's knowing how to test with the megger that makes it a great test tool.

Back in my grand dads days they used K&T in homes, and, they used the megger, to test the completed wiring as a system, and back then, they were crafstman and even took the time to draw up a wiring plan on the jobs, and signed their name to the work, your lucky today to find someone sober eniough to do a job, might be we should be careful who we give the craftsman title to, and bring back, so of the older skills, and values.

You can still find so of these plans tucked away in attics in older craftsman homes.

It anyone would like Pic's of NM Cable faults, found with a megger, please PM me and give me your e-mail address.

 

[don_resqcapt19]

I'm not sure how one conductor could get "burned" anyhow without substantial damage to its insulation.

I worked on one lightning repair job where the current "vaporized" a few inches of copper in a #16 wire in a range hood. There was no visible damage what so ever on that conductor...just some of the copper was missing inside of the insulation. This was an older building and had a mix of NM with ground and without ground. The only damaged equipment was the equipment that had a with ground supply conductor.

 

[bikeindy]

That's a "root cause" I've heard before, but I don't really like it when it is stated that way. The knick may have indeed been caused by a knife, but the use of the knife instead of strippers is not the cause. The improper use of the kinfe was the cause. I've used a knife to skin out cable jackets all my career, as many others have, and I don't have this problem.

Sorry I did state that poorly, I know guys who have used a knife all thier career as well but those of us who are too heavy handed with one really need a pair of stripers including the guy who did the home I was at didn't have my camera but the inside of those boxes were not great.

 

[mdshunk]

There was no visible damage what so ever on that conductor...just some of the copper was missing inside of the insulation.

Did you ship that section of conductor to the Ripley's Believe It Or Not museum or did you report the manufacturing defect to the company that made the wire? I'd have done one of the two.