Testing 230 volt ac circuits.

davidk65 | 13:20 Tue 27th Sep 2011 | DIY

3 Answers

I have 2 cables, an SWA and an MICC, running from my mains across a yard supplying electricity to 2 out buildings.
I intend to do an insulation check on these cables using a Megger. What readings would indicate a "fail" or "pass" on these cables or other circuits?

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The Builder

The bare minimum for domestic circuits is around 1 megohm.......... that really is low, though. Depending which Megger you have, they would normally (in a good new system) go off the scale ........... reading maybe 299 megohm.

davidk65

Question Author

Hi. Thank you for your reply.
I have just done a quick test using a 500 volt Megger.
Testing the MICC cable I got a reading of 200k.
Testing the SWA cable it was slightly higher at 500k.
To do the test I isolated both ends of both cables, but it was not possible for me to follow the whole of the cable run so I am not sure if the cables have been jointed somewhere along the way or if something has been taped off the cable somewhere. I think the installation is about 10 + years old.

The Builder

Mmm....... mineral cable should show an insulation resistance of tens of thousands of Megohms at normal temperatures.

Unless something has gone wrong with the tests, I can only think the insulation has broken down somewhere. Have you had tripping, or MCB problems with the circuits?

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