As long as they're not grounded or any load is present, that's all you need.

 

Thanks, Sparky.

So here's another dumb one. Let's say the opposite ends of the wires are exposed while testing. Wouldn't the exposed ends read as a point of insulation leakage in regards to the voltage passing through it (much like an exposed defected section of the wire)?

 

No, because there's no circuit for the leaking current to follow. It has to go somewhere for the meter to detect it.

 

Thanks again.

Just trying to understand how the meter would read any differently between having say a nick in the insulation that exposes copper, and leaving the ends also exposed during testing.

 

Short answer: No.

Longer answer: Maybe.

If you're doing testing at just a few kV this isn't likely to be a problem. But if for some reason the ends of your cable are excessively dirty or damp, you could have surface lakage that will lead to lower readings.

If you're ever doing any hipot testing, then you do have to bag the ends of the cables because ionizing the air will absolutely affect your reading.

For those higher voltage tests it's sometimes even necesdary to apply dielectric grease tonthe cable jacket to stop surface leakage.

 

...
If you're doing testing at just a few kV this isn't likely to be a problem. But if for some reason the ends of your cable are excessively dirty or damp, you could have surface lakage that will lead to lower readings.
...

And wire pulling lubricant is one of the most common sources of surface leakage when you are testing the conductors that you have just pulled in. The can look clean but still have enough lubricant on the surface so show low insulation resistance.

 

Start HERE it should clear up most of your questions and help you like it did many of us. :thumbup:

 

Thanks.

I actually had browsed through that right before I ask this question. But I didn't notice a clear reason why the wire ends don't need to be capped off during testing.

Maybe you can help explain or correct this analogy. The way I see it is like running water through a hose. If the end of the hose, or any other part of the hose is open, then that opening is responsible for the leakage. Isn't this the same basic principle as insulation testing?

 

Or are you saying something like: the meter will detect faults along the path of the wire, but once it gets to the end, it stops detecting because it's the end of the wire. So it wouldn't matter if the ends are exposed or not.

 

Not if in a dry atmosphere.

 

Nicked insulation that exposes the conductor under it isn't necessarily a fault. There's all sorts of uninsulated parts on a typical circuit. How much insulation is on the lugs in the panel (both the feeder/service, and the branch breaker)? What about all those screws on devices? Lampholders? Ever look into the business end of an installed wire nut and see bare copper? Just because you can see copper doesn't mean it's a fault. Sloppy work, maybe. But not a guaranteed fault.

I keep repeating this: A fault is an unintended path for current to flow. If the exposed conductor is not in contact with anything that is conductive, current cannot flow. Just like all those naked high-voltage conductors.... they're not in contact with anything conductive. And lugs in the panel. And device screws. And inside wire nuts.

 

So you agree with post 22 ???

 

Give us a break. You are new at this...right?

 

Start from scratch:

If you are using a megger as a go/no-go tester then you are testing for short circuts. You are not testing for cable damage becausr a megger doesn't detect that:

You can have a completely skinned open wire that will pass a megger test with flying colors, just as long as bare copper isn't close enough to a ground path to short circuit your test.

The megger does not know the difference between a deliberately cut cable end and an accidental tear in the insulation. If there isn't enough contamination on the surface of the wire, neither of those will allow enough surface tracking to give you poor readings.

 

Renfrey.
So you know that electricity doesn't pass through insulation right? Sometimes the insulation looks fine, or has been damaged by water, but actually the insulation has deteriorated and if you pass a enough voltage to the wire, the electricity WILL pass through the insulation to a conduit or another conductor.
A megger does that for you. It puts a higher voltage on the conductor and it gives you a resistance measurement between conductors and or the metal sheath/conduit.

Keep in mind if the insulation has been damaged but the damaged spot is not touching anything, (sheath, conduit, another conductor)the megger will read fine.

 

Renfrey should probably not own a megger or use it for anything. Sorry, bro. :001_huh:

 

Thank you so much, Big John, Sparky, and Eddy. Your last posts really clarified it for me.

 

Play with it, there is a video of testing paper that MAY help explain somewhat how a megger works.