On Sun, 17 Feb 2019 04:14:52 -0800 (PST), Kal Ico
wrote:

Thanks again for your steer.

I'm with you, Roger, that I think I will have mis-measured. Yes, I was using a low voltage AVO multimeter. I have a mains tester and even an insulation tester but would have to read up how to use them. (I qualified as 16th Edition, years ago, but not made use of this stuff in a long time. What is it they say about the brain - if you don't use it, you lose it!)

If you have to read up on how to use an insulation tester, you don't
really have the knowledge needed to diagnose the problem.

16th edition is meaningless. Anyone can pass the regs exam, you do not
have to have had even a miniscule amount of training or experience to
sit and pass the wiring regs test. Unless you have training or
experience, and your request for help on a very simple fault suggests
you haven't, get someone to look at it that does know where to start.

On the plus point most of the "advice" doesn't seem that bad. 'Pity to
have the equipment to diagnose the problem in minutes, yet not have
the solution.

For the solution you have to apply logic. Electrical diagnosis comes
into it, but you need a "system".

If you dig out the instructions for the Megger and have confidence
using it, you are well on your way to success. I would still ask an
electrically qualified aquaintance though :-)

AB