On 17/07/2019 09:31, Mathew Newton wrote:
On Wednesday, July 17, 2019 at 1:43:15 AM UTC+1, John Rumm wrote:

I should've said that this is a 2007-built house and so hopefully the
issue is not a result of some bizarre circuit design/layout.

In which case, yup, probably just a loose screw etc.

Also,
the E-E resistance is 0.9 ohms and all these readings are with a
non-zeroed meter (lead resistance measures at ~0.5 ohms) so whilst
they are all low it is the L-L/N-N inequality that raised my
suspicions rather than the absolute values, and given the
still-lowish N-N reading that's what led me towards it being a
contact point issue rather than a break or similar.

Yup, I would agree.

You could go for a "binary chop" type approach. Disconnect the
ends of the ring at the CU, and short L & N & E of one end
together. Now using a plug as a test point, plug it in somewhere on
the circuit near to where you think the middle might be. You can
now check if the L to E and N to E match. Whether they do or don't,
you have just eliminated half the circuit. Go half way again in
the appropriate direction, and you can get rid of half the
remaining ones again. Should take no more than Log_2(n) tests,
where n is the number of sockets on the circuit.

Okay that sounds doable - thanks. To be fair I think there are only
13 sockets so it's not that big an installation, and one or two of
those are spurs and thus wouldn't have contributed to the measured
resistance (their point of attachment would of course be - and
perhaps that's where it is quite likely to be?).

Something like one of these makes the job easy:

https://www.amazon.co.uk/Kewtech-KEW.../dp/B0058HZLTK



Hopefully this will be a one-off so a conventional plug with a
removable back should equally suffice, particularly given the power
will be off?

Yup the test sockets make it a bit easier (and safer), but working in a
controlled environment and with care, a normal plug and lead is fine. If
in doubt, you can always turn off everything at the main switch.


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/