Megging wiring

check here http://www.biddlemegger.com/biddle/A%20Stitch%20In%20Time.pdf

Depending on who you talk to, an insulation test is a necessary evil. Continual testing for some people is not a good thing while others believe it does no harm.

There have been several papers on the high voltage testing of cable, unfortunatly I can't find them to pass on, but there has been research into the damage continual high voltage testing does to cable. But the main word here is "CONTINUAL".

If you have a cable that is rated to 600 volts, (is it the voltage it will carry or the max rating of that cable?) you must consider the following; the reading you get at 1000 v which is suitable for this cable, will depend on temperature of the cable, the length and therefore the cable resistance.

You make no reference to what is connected to the end of the cable, or is it just a length of 3 core cable(?), does the cable have armour? So the test would be phase to phase and then each phase to earth(armour)

To keep it simple, test at 1000 volts, with nothing connected to the cable. Do not test further at higher voltages, no need as the result would be the same. Your first test, depending on the length of the cable you will see, (with long lengths of cable) a slow build up to infinity, and the opposite for short lengths. Do not remove the insulation tester immediately after you complete the test as the "Megger" will discharge the voltage build up in the cable, as was mentioned in an earlier reply. Leave it connected for a few minutes.

Please read the safety instructions of the instrument you are using and make sure you have the leads connected correctly as you will either have no reading or a reading you are not sure of.

You should see a reading of infinity or close to depending of the factors I mentioned earlier.