Robin 1651 (calibrated) insulation test readings, 500V-DC, L/N shorted
v E.

Final circuit consists of 8m FTE2.5, 13m SWA-PVC-2.5-2-core to
a CU with 12m of FTE2.5 & 20m FTE1.5 for power & lighting ring.
All bulbs removed, all switches on, lighting switches are 1-way.
Cable tested at source with RCD removed (ie, whole cable run).

After removing the tell-tale neon (0.32Mohm) I get an insulation
resistance of 1651Mohms which seems unusually high/good.

Is the calibration stuffed or is this reading correct?
Set to 2000Mohm, 500VDC (200Mohm & 20Mohm range all OR).

IIRC PVC typically has insulation resistance of 200Mohms/km,
and resistance halves with every doubling of distance. So the
figure is not untoward - I expected 15-25 for a 1980 final circuit.
This is fully wired up, all fittings, bulbs removed, not bare reels.

Testing the meter on 3ft of shagged (technical term) butyl cable
from 1947, crumbling & disintegrated insulation, showed infinity
as the IR even on the 1000V-DC test. That I think is complete
******** because it should carbon track - it could not pass.


Doing basic IR tests before a BCO outsources same and we
get a PIR done generally. I have to replace a surface run of
SWA elsewhere (2-core, armour exported earth) due to a nick
in the sheath showing flaking rust. Conventional wisdom is
not to export the earth even if no Class-1 devices (in garage).
However with many 24" railway drains just 3-4ft below ground
I do not feel like SDSing 4ft earth rods at random. Last person
who damaged one found knee deep water & a £7k repair bill.

Thanks.