OP
DanMulhare
DIY
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It should not matter which way round for a simple short circuit style of fault. What you see with it initially low "resistance" and then rising is typical of charging capacitance (the meter measures the current flowing, so with a capacitor it is initially large and then drops as its voltage increases towards that of the source due to the accumulated charge).
Now all cable has capacitance, but I'm a little surprised to see enough of it to show up in your test but have no experience with your type of meter to know if that is reasonable or not.
The last thing you would try is a similar set of tests (both directions) using the diode check (arrow symbol) to see if anything electronic appears. Otherwise it looks as if the fault might be intermittent or not as simple as a E-N short (though it really looks like it).
Again if you had access to a proper insulation tester to check as 250V it would answer the question in a more certain manner.
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With the RCD off are you testing from the related strip of neutral terminals? (i.e. checking from RCD output's N to Earth)
Apologies I was testing all back to the corresponding N bar for the 80A RCD.
Further test below.
Test 5a and 5b
Testing at 2M
80A RCD in the off position
63A RCD in the on position
Red probe to E
(5a)
Black probe to N bar for the 80A RCD
Reading goes above 1 immediately and continues to rise
(5b)
Black probe to N bar for the 63A RCD
No reading at all.
I then switched to test at 200M and got a readings between 138 and 156 but only for a second before it would read 1 again.
Test 6a and 6b
Testing at 2M
80A RCD in the on position
63A RCD in the off position
Red probe to E
(6a)
Black probe to N bar for the 80A RCD
Reading goes above 1 immediately and continues to rise
(6b)
Black probe to N bar for the 63A RCD
No reading at all.
I then switched to test at 200M and got a readings between 138 and 197 but only for a second before it would read 1 again.
Conclusion when isolating and testing the separate N bars for both the 80A and 63A RCD’s the tests for the 63A RCD is the one I need to switch from 2M to 200M to see any reading and it’s not consistent or even going up.
Does this mean there is a N-E fault on one of the circuits fed off the 63A RCD?