Electrician Talk banner
1 - 6 of 6 Posts

·
Registered
Joined
·
3 Posts
Discussion Starter · #1 ·
I just bought my first megger and have been experimenting to help me better understand readings. Using a chunk of 14/2 bx I attach one lead to the armour and the other lead to a stripped end of the conductor. On 250 500 and 1000 volt settings my reading is always OL. Being that the megger is rated for 2000Mohms I expected that to be the max value and not OL. I then took strippers and cut and nicked the conductor insulation in various places expecting it would show some variation in my reading but still read OL. unless I am not properly understanding the megger should I not get some leakage due to the damaged insulation and also why do I read OL in perfect conditions instead of the meter max of 2000Mohm? Any help is greatly appreciated.
 

·
Registered
Joined
·
3,838 Posts
The resistance of air across the gap you created is greater than the range of you meter. In general, you need to have some type of contaminate between the conductors to get a reading.

Just because you have bare wires does not mean you will detect that using that type of meter. This is something that many users do not understand.
If you are pulling in conductors without the use of a pulling lube, something that is more common with the new "slick" wire jackets, you can have a damaged conductor with bare copper that will not show up when you use an insulation resistance tester, but once that conduit fills with water the conductor will fail.
 

·
Registered
Joined
·
1,802 Posts
  • Like
Reactions: pete87

·
Registered
Joined
·
3 Posts
Discussion Starter · #4 ·
Thanks for the links I will check them out.....based on what I mentioned in my post is there something obvious that im missing? I get the concept and I know other meggers to show their max value as a M omic value and not OL.....just questioning due to the laughing...
 

·
Registered
Joined
·
1,802 Posts
megging a chunk of wire is actually useless because the conductor is actually too short unless contaminated by water or oil
If i remember correctly (and i could be wrong on this) I believe a conductor needs to be at least 6 or more meters in length
a good test for experimenting is an old extension cord

also never meg a circuit unless you make sure anything electronic has been disconnected or it could end up costing you
 
1 - 6 of 6 Posts
Top