Testing conductor insulation

[AES1005]

Wanted to see if I was missing something? I connected my digital megger with three voltage settings, using the 500 v range connected the + to the bare part of the wire and the - to the outer insulation. (which I damaged on purpose for the test). Ran the test for 60 sec. meter read 4000+mohm. went up the scale 1000v no change. Anyway the only way I could get any type of reading was when I connected the meter + to the bare conductor and the - around the same wire coated with a piece of paper, only then did readings show insulation leakage. So my question is the digital meggers must only be good for very small applications?

 

[Buck Parrish]

Maybe it was to dry, or the conditions were not right for the leak.
Maybe some one else will respond.

 

[Flex]

on our digital megger at work, one lead goes on the conductor the other gets grounded.

 

[brian john]

FLEX: It is very difficult to test in this way.

If you want to do a test

Utilizing a sheet of paper, the thinner the better such as phone messages, but with a little work standard ruled paper will work. Take a soft pencil and scribble on the paper with copious amounts of lead surfaces at the points where the alligator clips will connect. Between these two points make random scribbles.

Set the megger at 1000 VDC and you should see sparks, arcs and flame, double click on the picture below.

 

[Buck Parrish]

FLEX: It is very difficult to test in this way.

If you want to do a test

Utilizing a sheet of paper, the thinner the better such as phone messages, but with a little work standard ruled paper will work. Take a soft pencil and scribble on the paper with copious amounts of lead surfaces at the points where the alligator clips will connect. Between these two points make random scribbles.

Set the megger at 1000 VDC and you should see sparks, arcs and flame, double click on the picture below.

Thanks Brian, That's a good slide show.

But how does that test the insulation.
Lead will conduct electricity.
The megger is testing isulating material.

 

[76nemo]

Wanted to see if I was missing something? I connected my digital megger with three voltage settings, using the 500 v range connected the + to the bare part of the wire and the - to the outer insulation. (which I damaged on purpose for the test). Ran the test for 60 sec. meter read 4000+mohm. went up the scale 1000v no change. Anyway the only way I could get any type of reading was when I connected the meter + to the bare conductor and the - around the same wire coated with a piece of paper, only then did readings show insulation leakage. So my question is the digital meggers must only be good for very small applications?

Must say I have never heard of testing insulation that way :roll:

 

[iwire]

Must say I have never heard of testing insulation that way :roll:

The only time I have heard of that was when the shop had a salesman come out to teach us how to use a Megga. :roll:

That may be a carry over from testing higher voltage conductors that have a shield you could hook to.

For run of the mill 600 volt building wiring I imagine conductor to ground would be the way to test.

 

[AES1005]

Thanks for the input guys, I belive the one lead to ground is the problem with my experiment. I'll have to set up something like that. and try the pencil lead thing.

Online at www.aemc.com they do show connecting the leads on the cable in one illistration to the wire only. But they are using a meter with the third ground lead.

 

[76nemo]

What in particular are you wanting to utilize an Insulation tester for AES?

 

[brian john]

Test the paper without pencil, Testing the insulation would require the cut you made to me in contact with water and or a grounded surface. The conductor insulation is good enough to test for a breakdown such as you set up it would be tough. Try a higher voltage, all insulation will break down if you have sufficient voltage to bridge the insulation.

 

[brian john]

on our digital megger at work, one lead goes on the conductor the other gets grounded.

Not necessarily, depends on what you are testing.