On 28/05/2019 19:10, ARW wrote:
Only posting to point out the point of testing and keeping proper
records for additions to electrical circuits.

Today's first job was to sort the low ME reading.

A work colleague had already identified the cause as the "twinkly
lights" above the bath (just to point out that these are lots of very
small fibre optic lights in some boxing above a bath in a children's
hospice) so permission and an agreed time to was needed to forcibly
remove the side panels of the boxing in for further investigation.

And the cause was that the PSUs of the fibre optic lights were plugged
into an RCD socket behind the boxing in. The RCD socket was the cause of
the low NE reading.

The lights were fitted by volunteers a few years ago.

However then came my second job.

High Zs on drive lights (same place). Yep but only high because they
were not designed correctly in the first place (and a pro designed that
11 years ago). The Zs reading of 1.8 ohms was lower than my guess of
20.0 to 2.5 ohms based on pacing out the length of the driveway.

Now the lights have been changed from sodium to LED and so rather than
checking the tightness of every earth terminal (which IMHO would do
nothing) I just swapped the MCB from a C type to a B type.


Interesting.

Bill