meggering romex

[electricalperson]

today i was experimenting with my megger. i was testing it using the 1000v scale. i cut the insulation across the entire cable with my razor knife so the black and white were knicked then i tested that and everything was ok. then i wet the cable with a little bit of water and tested between the black and bare. all of a sudden it started to spark where i cut it and melted a little bit and smelled of burning plastic. is this something i should worry about if i test a piece of cable (mc, old bx, old romex etc..) inside of a house. i dont want to start any fires or worry the people living there. should i test it at 500v instead because it didnt spark then?

 

[mdshunk]

Yeah, I don't normally test at more than twice the normal operating voltage. I don't think there's much fear of setting a house alight with a megger, however.

Bravo to you for experimenting.

 

[electricalperson]

thanks for the help

 

[electricalperson]

i already learned a lot more with just a few hours of experimenting with my new toy:smile:

 

[GilbeSpark]

electricalperson, what megger are you using?

I was experimenting with the megger and nm and I smashed the wire with a hammer a couple of times and still got full scale readings. Seemed odd, as I know the insulation was smashed enough to where bare conductor was showing. What other experimenting have you done with the nm cable?

 

[mdshunk]

Seemed odd, as I know the insulation was smashed enough to where bare conductor was showing.

Doesn't sound odd at all to me. If the conductor was showing, but wouldn't show even the lowest level short on a megger, then there is no hazard. Consider that the first electrical installations used bare wire, and transmission is still that way today.

 

[electricalperson]

i have a model mj159 megger its a hand crank. thats the first time ive actually sat down and messed around with this. im trying to get some other type of wire and mess around with it the same way.

 

[mdshunk]

i have a model mj159 megger its a hand crank. thats the first time ive actually sat down and messed around with this. im trying to get some other type of wire and mess around with it the same way.

Throw some old BX (with the cloth covered conductors) in a bucket of water, and take megger readings. Take it out of the water, and megger it on consecutive days. It takes a very long time for the "short" to disappear in that stuff.

Megger almost any underground piece of UF cable that has been in the ground a number of years, and you'll often get a failure reading too. When you start troubleshooting direct buried cables and conductors in the coming years, you'll start to curse the guys who don't use conduit for u/g runs.

 

[BryanMD]

i have a model mj159 megger its a hand crank. thats the first time ive actually sat down and messed around with this. im trying to get some other type of wire and mess around with it the same way.

Beaver! You come back into the house this minute. Your dinner is getting cold or Wally will be late to his basketball game!

 

[electricalperson]

Beaver! You come back into the house this minute. Your dinner is getting cold or Wally will be late to his basketball game!

????:roll:

 

[BryanMD]

????:roll:

whooosh!

Beaver and Wally: aww Mom, we're just messing around!

 

[480sparky]

whooosh!

Beaver and Wally: aww Mom, we're just messing around!

"Gee, Beav. Wait 'till Dad gets home. Then you're really gonna get it!"​

 

[HighWirey]

meggering romex

electricalperson,

Good news on you experimenting with your megger. Gaining experience on the job with a brand new shiny instrument is not professional. Keep learning.

MDShunk posted:
"Megger almost any underground piece of UF cable that has been in the ground a number of years, and you'll often get a failure reading too. When you start troubleshooting direct buried cables and conductors in the coming years, you'll start to curse the guys who don't use conduit for u/g runs"

Amen, MD.

As a pup I used to volunter my time at the Little League field repairing their stuff. Had to give it up. Most of my time was spent digging up and repairing problems related to those 2/0 aluminum direct buried field light feeders. In Florida's salt sand, yet! Could have paid for a lot of that missing PVC.
Mr. Megger told me which conductor was faulty, he just did not tell me where. Oh, BTW guess your megger manual forgot to mention having to first remove all that sticky 'cheap tape' from the bugnuts to isolate the wire segments. Then do the same thing to the next segment. Sometimes there are mosquitos, and darkness. On and on . . .

Didn't know about the 'thumper' till later. Still don't. Ask Marc or Google.

Best Wishes Everyone

 

[ptonsparky]

i already learned a lot more with just a few hours of experimenting with my new toy:smile:

Hint - Never EVER refer to these tools as toys in front of spouse. :grin:

 

[frenchelectrican]

electricalperson,

Good news on you experimenting with your megger. Gaining experience on the job with a brand new shiny instrument is not professional. Keep learning.

Didn't know about the 'thumper' till later. Still don't. Ask Marc or Google.

Best Wishes Everyone

MDshunk or myself ??

MDshunk have few diffrent kinds of meggers i think he have at least 3 but i maybe wrong on that but i will let him speak about his view of using megger and thumper.


For myself.,, yeah i used the thumper from time to time but only one quirk you have to becarefull with it. a simple rules is disconnect any conductors off first before you use the megger or thumper.

the thumper is pretty acture down about 3 feet [ apx 1 metre ] down but more deeper it get pretty hard to get a good signal but can be tracable.

Merci, Marc

 

[HighWirey]

frenchelectrician posted:
"MDshunk or myself ??"

My apology Marc, I will be more specific in the future.

Did not know you had to 'isolate' when using the thumper also. That is why we are all here, to share and learn.

Always located my voltage 'leaks' using the VOM 'probe de dirt' method.

Best Wishes Everyone

 

[masterelect1]

more experimenting

more experimenting

Take a single conductor (THHN #12) and nick it. lay the conductor inside EMT or RMC. Connect one megger lead to the conduit and the other to the conductor and "megger away" - you should see a "0" or very close to it. This indicates the conductor insulation to ground.

 

[don_resqcapt19]

masterelect1,

Take a single conductor (THHN #12) and nick it. lay the conductor inside EMT or RMC. Connect one megger lead to the conduit and the other to the conductor and "megger away" - you should see a "0" or very close to it. This indicates the conductor insulation to ground.

I don't think so, unless the copper is touching the conduit. Even using a 1000 volt setting on the megger you should see near infinity in this case. The megger voltage will not jump the gap between the bare part of the conductor and the conduit. Now if you put wire pulling lube or some other conductive material on the wire, you will have a low megger reading.
Don

 

[electricalperson]

Megger almost any underground piece of UF cable that has been in the ground a number of years, and you'll often get a failure reading too. When you start troubleshooting direct buried cables and conductors in the coming years, you'll start to curse the guys who don't use conduit for u/g runs.

so if i get a bad reading on a piece of UF cable does it mean the cable is bad or is it because its in the ground?

 

[electricalperson]

electricalperson,

Good news on you experimenting with your megger. Gaining experience on the job with a brand new shiny instrument is not professional. Keep learning.

well im going to have to bring it into the real world sooner or later. probably to use on transformers and motors since i cant afford to buy them to experiment at home with. ill just make sure to read up on insulation testing that kind of equipment and fully understand what ill be looking for before i dive into it:grin: