weird IR test results with RCDs

[Benny_Boy]

Hi guys,

I'm doing some revision for 2391 and I've built a test rig to practice on, just one radial (lights) and a ring.
The testing was all going fine until the IR tests.

Results were as follows

Whole installation:

R1 to Rn = 0.13MOhms
(R1+Rn) to R2 = >299MOhms
R1 to R2 = >299Mohms
R2 to Rn = >299Mohms



I thought I must have made a stupid mistake when wiring up but individual IR tests on the radial and the ring all come out as >299MOhms.

long story short, I put the probes across the RCD inl the various Phase to Neutral combinations and found that when the rcd was off putting the probes at the bottom gave a reading of 0.24MOhms

as shown here:

When it was switched on the reading stayed the same then when I switched both the RCDs on with neither the ring or radial connected the reading dropped to 0.13Mohms indicating a parallel path through both rcds?

Boths RCDs behave in the same way

The 100A breaker checks out ok.
Are these just a pair of crap/dangerous RCDs or am I being a berk?
I realize that I've probably made some stupid mistake or am ignoring some blindingly obvious reason for this but I can't see it!

Any comments or suggestions gratefully received.

cheers
Ben

PS I should just say that before I posted this I removed all wiring except that which came with the board and retested with the same results.

 

[JulianC]

Sounds like you're reading through the RCD internals. Disconnect line and neutral from the relevant protective devices before carrying out IR tests.

 

[acat]

Beat me to it Julian Ive just done the same test but as mentioned but disconnected and got the >299


Chris

 

[Benny_Boy]

Sounds like you're reading through the RCD internals. Disconnect line and neutral from the relevant protective devices before carrying out IR tests.

What a donut!

sorry!

cheers
Ben

 

[scotsparky]

when your doing the test remember IR method 2 in GN3 isolate combine phase and neutran and then test between them and earth means you have no potential difference between line conductors so no need to strip out lights ect. far faster as well.

 

[Benny_Boy]

when your doing the test remember IR method 2 in GN3 isolate combine phase and neutran and then test between them and earth means you have no potential difference between line conductors so no need to strip out lights ect. far faster as well.

that actually makes a ton of sense. I did in fact perform that test and got >299 on the whole installation but couldn't work out why I was getting dodgy readings from r1 to rn.

That little nugget allows another piece of the puzzle to slot into place.

Thanks!

Ben