Hi All

I have a consumer unit problem that is driving me up the wall !
I installed a Crabtree split-load dual rccb unit in a house with a TT
supply, but am having trouble with the split-load rccb (63A 100mA) in
that it will not trip using the test button. It does trip however as
soon as I put a load on any of the MCBs it feeds.

I naturally thought that the rccb was faulty and swapped it for
another but this does the same??
The test button operation of the rccb is not rocket science - you
press the button which puts a resistive load across live and neutral,
the fault sensing winding then trips the rccb. So why doesn't this
work??

I now have a 3rd rccb to try but I am confident this will not help
things. This has never happened before and the supplier also confirms
that repeated failures of crabtree gear is unheard of - it just
doesn't happen (though its not impossible)

Any ideas?

The other rccb (80A 3mA) in the CU is working fine and trips as
expected when tested.

wrote in message
ps.com...
Hi All

I have a consumer unit problem that is driving me up the wall !
I installed a Crabtree split-load dual rccb unit in a house with a TT
supply, but am having trouble with the split-load rccb (63A 100mA) in
that it will not trip using the test button. It does trip however as
soon as I put a load on any of the MCBs it feeds.

I naturally thought that the rccb was faulty and swapped it for
another but this does the same??
The test button operation of the rccb is not rocket science - you
press the button which puts a resistive load across live and neutral,
the fault sensing winding then trips the rccb. So why doesn't this
work??

I now have a 3rd rccb to try but I am confident this will not help
things. This has never happened before and the supplier also confirms
that repeated failures of crabtree gear is unheard of - it just
doesn't happen (though its not impossible)

Any ideas?

The other rccb (80A 3mA) in the CU is working fine and trips as
expected when tested.

Check that all the neutral tails are in the correct bus bars. I have had two
Wylex CUs (made by the same people as Crabtee) where the neutral tails were
in the wrong busbar and had identical symptoms.

Adam

Cheers for the thoughts

I have removed the links so that N1, N2, and N3 are separated and
wired as per the tech diagram for this configuration.

Basically both rccb's get the common supply neutral (N1) into them and
they feed the separate neutrals (N2 and N3) out the other side.

I really am scratching over my head over this one, and am on 1st name
terms with Crabtree technical haha!

Cheers

Oldskool

Cheers for the thoughts

I have removed the links so that N1, N2, and N3 are separated and
wired as per the tech diagram for this configuration.

Basically both rccb's get the common supply neutral (N1) into them and
they feed the separate neutrals (N2 and N3) out the other side.

I really am scratching over my head over this one, and am on 1st name
terms with Crabtree technical haha!

Cheers

Oldskool

formulated the question :
I naturally thought that the rccb was faulty and swapped it for
another but this does the same??

Something rather odd here.

The test button operation of the rccb is not rocket science - you
press the button which puts a resistive load across live and neutral,
the fault sensing winding then trips the rccb. So why doesn't this
work??

That is not how it works!

The button connects between L and E via a resistor which causes an
imbalance between the L and N (not passing an equal current through
both conductors), the imbalance is what causes it to trip.

Should the button be between L and N then pressing it would not make
any difference as the load would remain equally balanced through the
two conductors.

Combine that with it tripping when ever you do put a load on via an MCB
- leads me to suggest that you have crossed or swapped the N & E
somewhere in the board.

--

Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk

"Harry Bloomfield" wrote in message
...
formulated the question :
I naturally thought that the rccb was faulty and swapped it for
another but this does the same??

Something rather odd here.

The test button operation of the rccb is not rocket science - you
press the button which puts a resistive load across live and neutral,
the fault sensing winding then trips the rccb. So why doesn't this
work??

That is not how it works!

The button connects between L and E via a resistor which causes an
imbalance between the L and N (not passing an equal current through both
conductors), the imbalance is what causes it to trip.

Should the button be between L and N then pressing it would not make any
difference as the load would remain equally balanced through the two
conductors.

Combine that with it tripping when ever you do put a load on via an MCB -
leads me to suggest that you have crossed or swapped the N & E somewhere
in the board.

--

Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk


Beat me to it - fits the symptoms perfectly

Nick

"Harry Bloomfield" wrote in message
...
formulated the question :
I naturally thought that the rccb was faulty and swapped it for
another but this does the same??

Something rather odd here.

The test button operation of the rccb is not rocket science - you
press the button which puts a resistive load across live and neutral,
the fault sensing winding then trips the rccb. So why doesn't this
work??

That is not how it works!

It is how it works! The test button is connected to the opposite sides of
the sensing coils on the RCD between live and neutral. Most RCDs have a
picture of this on them.

Adam

"ARWadsworth" wrote in message
k...

"Harry Bloomfield" wrote in message
...
formulated the question :
I naturally thought that the rccb was faulty and swapped it for
another but this does the same??

Something rather odd here.

The test button operation of the rccb is not rocket science - you
press the button which puts a resistive load across live and neutral,
the fault sensing winding then trips the rccb. So why doesn't this
work??

That is not how it works!

It is how it works! The test button is connected to the opposite sides of
the sensing coils on the RCD between live and neutral. Most RCDs have a
picture of this on them.

Adam
Adam,
The resistor simulates leakage to Earth - by connecting a conductor (Phase
or Neutral) to Earth.

Normally, current flows between the two conductors and this is when it
should NOT trip.

Only when the current is different in each of the flow/return conductors (
i.e. some to Earth)
should it trip. The coils for the trip circuit are contra-wound so equal
current, in each, balances
and no trip is caused

"Nick" wrote in message
...

"ARWadsworth" wrote in message
k...

"Harry Bloomfield" wrote in message
...
formulated the question :
I naturally thought that the rccb was faulty and swapped it for
another but this does the same??

Something rather odd here.

The test button operation of the rccb is not rocket science - you
press the button which puts a resistive load across live and neutral,
the fault sensing winding then trips the rccb. So why doesn't this
work??

That is not how it works!

It is how it works! The test button is connected to the opposite sides of
the sensing coils on the RCD between live and neutral. Most RCDs have a
picture of this on them.

Adam
Adam,
The resistor simulates leakage to Earth - by connecting a conductor (Phase
or Neutral) to Earth.

Normally, current flows between the two conductors and this is when it
should NOT trip.

Only when the current is different in each of the flow/return conductors
( i.e. some to Earth)
should it trip. The coils for the trip circuit are contra-wound so equal
current, in each, balances
and no trip is caused

Crabtee RCDs have Lin, Lout, Nin and Nout. Four connections and NO earth.

Adam

wrote in message
oups.com...
Cheers for the thoughts

I have removed the links so that N1, N2, and N3 are separated and
wired as per the tech diagram for this configuration.

Basically both rccb's get the common supply neutral (N1) into them and
they feed the separate neutrals (N2 and N3) out the other side.

I really am scratching over my head over this one, and am on 1st name
terms with Crabtree technical haha!


You can test the 100mA RCD by swapping it with the 30mA one. Easy and cost
free.

If the test button works when you have swapped them then assume the RCD
works.

Adam

Crabtee RCDs have Lin, Lout, Nin and Nout. Four connections and NO earth.

Adam


In which case, the only way the test button can work is to connect a
resistor from the L output to the N input ( or vice versa ), so the test
current flows through the L current sense , but not the N sense. ( or vice
versa )

In this case, the test function is 100% within the RCD, and does not depend
on external wiring. If the test button fails to trip it, it must be
faulty.

So it revolves around exactly how the test button works.
Does is actually attempt to flow some curent to earth, or does it just flow
some current in one leg which remains un-accounted for in the other? I
think we should be told :-)

--
Ron

Ron Lowe submitted this idea :

Crabtee RCDs have Lin, Lout, Nin and Nout. Four connections and NO earth.

Adam


In which case, the only way the test button can work is to connect a resistor
from the L output to the N input ( or vice versa ), so the test current flows
through the L current sense , but not the N sense. ( or vice versa )

In this case, the test function is 100% within the RCD, and does not depend
on external wiring. If the test button fails to trip it, it must be
faulty.

So it revolves around exactly how the test button works.
Does is actually attempt to flow some curent to earth, or does it just flow
some current in one leg which remains un-accounted for in the other? I
think we should be told :-)

You are correct Ron, I have just checked my DB in the garage! So the
test button must connect a resistor in series with one of the windings,
as well as applying a small load to the output. Still amounts to the
same thing - he has some how managed to get his connections wrong.

--

Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk

"Ron Lowe" ronATlowe-famlyDOTmeDOTukSPURIOUS wrote in message
...

Crabtee RCDs have Lin, Lout, Nin and Nout. Four connections and NO earth.

Adam


In which case, the only way the test button can work is to connect a
resistor from the L output to the N input ( or vice versa ), so the test
current flows through the L current sense , but not the N sense. ( or vice
versa )

In this case, the test function is 100% within the RCD, and does not
depend on external wiring. If the test button fails to trip it, it must
be faulty.

So it revolves around exactly how the test button works.
Does is actually attempt to flow some curent to earth, or does it just
flow some current in one leg which remains un-accounted for in the other?
I think we should be told :-)

http://www.memonline.com/rcd1.html

Is the best I can find at the monent. Notice the words

"A test circuit is also incorporated whereby connection is made from load
phase to supply neutral via a TEST COIL and RESISTOR and activated by a TEST
BUTTON."

Adam

"Ron Lowe" ronATlowe-famlyDOTmeDOTukSPURIOUS wrote in message
...

Crabtee RCDs have Lin, Lout, Nin and Nout. Four connections and NO earth.

Adam


In which case, the only way the test button can work is to connect a
resistor from the L output to the N input ( or vice versa ), so the test
current flows through the L current sense , but not the N sense. ( or vice
versa )

In this case, the test function is 100% within the RCD, and does not
depend on external wiring. If the test button fails to trip it, it must
be faulty.

Not if there is no neutral present. You need the potential difference to
make the current.

Adam

I now have a 3rd rccb to try but I am confident this will not help
things. This has never happened before and the supplier also confirms
that repeated failures of crabtree gear is unheard of - it just
doesn't happen (though its not impossible)


Any ideas?


Last year I had 3 Wylex split load CUs in a row where the RCD was
faulty straight out of the box. Different problem, would not latch
closed. (before installation).

Allan

You are correct Ron, I have just checked my DB in the garage! So the
test button must connect a resistor in series with one of the windings,
as well as applying a small load to the output. Still amounts to the
same thing - he has some how managed to get his connections wrong.

I have checked the technical drawings in the Crabtree catalogue and it
is definitely correct.

It does appear that the test facility is entirely within the rccb and
there is no connection to earth at all. I'm not sure how I could get
my connections wrong as this should function work within the CU
independant of any connections with regard to the domestic circuits.

Snippet from the rccb installation instructions:

1)The incoming cables to the rccb may be taken either to the top or
bottom set of terminals, dependant entirely on the ease of wiring the
device

2) As the rccb works on the current balance principle, all cables
feeding the protected installation (live and neutral) must be
connected to the device. If this is not complied with, continuous
nuisance tripping of the breaker will result when power is drawn from
the supply.

I know that no.2 above sounds like I haven't connected a neutral but
if that were the case the other rccb wouldn't work either..

3) Having installed the unit and switched on the rccb, press the test
button in order to test the correct function of the device. This ONLY
tests the operation of the rccb and not the continuity or value of
earth resistance path

Surely a rudimentary test would be for me to connect one set of the L
& N on the rccb to a flying lead plugged into my socket ring main and
hit the test button?
This would save me trekking over to the installation yet again to find
it not work again!

Thanks for all your views

On 28 Feb, 16:48, wrote:
Hi All

I have a consumer unit problem that is driving me up the wall !
I installed a Crabtree split-load dual rccb unit in a house with a TT
supply, but am having trouble with the split-load rccb (63A 100mA) in
that it will not trip using the test button. It does trip however as
soon as I put a load on any of the MCBs it feeds.

I naturally thought that the rccb was faulty and swapped it for
another but this does the same??
The test button operation of the rccb is not rocket science - you
press the button which puts a resistive load across live and neutral,
the fault sensing winding then trips the rccb. So why doesn't this
work??

I now have a 3rd rccb to try but I am confident this will not help
things. This has never happened before and the supplier also confirms
that repeated failures of crabtree gear is unheard of - it just
doesn't happen (though its not impossible)

Any ideas?

The other rccb (80A 3mA) in the CU is working fine and trips as
expected when tested.

Sounds as though the live input and output of the RCD is wired in
opposite direction through the neutral input and output. The intended
cross path provided by the test button will not cause imbalance. Any
normal current will immediately trip the unit.
Check the input live and neutral go to the right input terminals and
the output goes to the load @(i.e. the MCB busbar and the protected
Neutral rail) Most likely error is in the neutral connections
If this is not the case try posting a photo on a suitable site.

wrote:

Surely a rudimentary test would be for me to connect one set of the L
& N on the rccb to a flying lead plugged into my socket ring main and
hit the test button?

Yes, that should work.

Thanks for all your views

How about providing a close-up photo of your CU internal wiring in-situ?
Someone might then be able to spot something...

--
Andy

In article om,
wrote:
I now have a 3rd rccb to try but I am confident this will not help
things. This has never happened before and the supplier also confirms
that repeated failures of crabtree gear is unheard of - it just
doesn't happen (though its not impossible)

Any ideas?

Assuming you've wired the CU correctly, I'd be looking for a neutral funny
elsewhere. Something like a shared neutral.

--
*When the chips are down, the buffalo is empty*

Dave Plowman London SW
To e-mail, change noise into sound.

Snippet from the rccb installation instructions:

1)The incoming cables to the rccb may be taken either to the top or
bottom set of terminals, dependant entirely on the ease of wiring the
device

The source L & N must be taken AS A SET to either the top or bottom
SET of terminals.

The output L & N is from the other SET (top or bottom).

Splitting the sets will cause the exact symptoms you describe.

If that is the case, how do you propose I connect it up in light of
the following rccb terminal layout:

There is a neutral connection on the top of the rccb.
On the bottom there are two live terminal pins (which plug directly
into the CU busbar) and a neutral connection

The unit is a Crabtree split-load rccb part no 363/s100

What would you do?

Cheers

On 1 Mar 2007 04:15:58 -0800, mused:


Snippet from the rccb installation instructions:

1)The incoming cables to the rccb may be taken either to the top or
bottom set of terminals, dependant entirely on the ease of wiring the
device

The source L & N must be taken AS A SET to either the top or bottom
SET of terminals.

The output L & N is from the other SET (top or bottom).

Splitting the sets will cause the exact symptoms you describe.

If that is the case, how do you propose I connect it up in light of
the following rccb terminal layout:

There is a neutral connection on the top of the rccb.
On the bottom there are two live terminal pins (which plug directly
into the CU busbar) and a neutral connection

The unit is a Crabtree split-load rccb part no 363/s100

What would you do?

Well, I'd fix it using m skills as an electrician to test everything
and make 300% sure everything is actually the right polarity.

Simple really, but you haven't filled me with confidence so I'm
guessing you haven't been through and tested everything?
--
Regards,
Stuart.

In article .com,
wrote:
The source L & N must be taken AS A SET to either the top or bottom
SET of terminals.

The output L & N is from the other SET (top or bottom).

Splitting the sets will cause the exact symptoms you describe.

If that is the case, how do you propose I connect it up in light of
the following rccb terminal layout:

There is a neutral connection on the top of the rccb.
On the bottom there are two live terminal pins (which plug directly
into the CU busbar) and a neutral connection

The unit is a Crabtree split-load rccb part no 363/s100

Are you missing the two neutral buss bars? One is used for the non RCD
protected side, the other for the RCD protected. And both neutrals from
say a ring must go to the correct one.

I'd switch everything off (including MCBs) and check the resistance
between the two bars. It should be near infinite.

--
*Organized Crime Is Alive And Well; It's Called Auto Insurance. *

Dave Plowman London SW
To e-mail, change noise into sound.

explained on 28/02/2007 :
Surely a rudimentary test would be for me to connect one set of the L
& N on the rccb to a flying lead plugged into my socket ring main and
hit the test button?

My understanding of it suggests that nothing needs to be connected to
the output of the RCD, for it to be tripped by pressing the test button
- all it should need is a L & N on the input.





--

Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk

wrote in message
ups.com...
You are correct Ron, I have just checked my DB in the garage! So the
test button must connect a resistor in series with one of the windings,
as well as applying a small load to the output. Still amounts to the
same thing - he has some how managed to get his connections wrong.

I have checked the technical drawings in the Crabtree catalogue and it
is definitely correct.

It does appear that the test facility is entirely within the rccb and
there is no connection to earth at all. I'm not sure how I could get
my connections wrong as this should function work within the CU
independant of any connections with regard to the domestic circuits.

Snippet from the rccb installation instructions:

1)The incoming cables to the rccb may be taken either to the top or
bottom set of terminals, dependant entirely on the ease of wiring the
device

2) As the rccb works on the current balance principle, all cables
feeding the protected installation (live and neutral) must be
connected to the device. If this is not complied with, continuous
nuisance tripping of the breaker will result when power is drawn from
the supply.

I know that no.2 above sounds like I haven't connected a neutral but
if that were the case the other rccb wouldn't work either..

3) Having installed the unit and switched on the rccb, press the test
button in order to test the correct function of the device. This ONLY
tests the operation of the rccb and not the continuity or value of
earth resistance path

Surely a rudimentary test would be for me to connect one set of the L
& N on the rccb to a flying lead plugged into my socket ring main and
hit the test button?
This would save me trekking over to the installation yet again to find
it not work again!

With the 100mA RCD switched off, what voltage do you read between the top
right N connection and the main incoming live?

Adam

On 1 Mar, 12:15, wrote:
Snippet from the rccb installation instructions:

1)The incoming cables to the rccb may be taken either to the top or
bottom set of terminals, dependant entirely on the ease of wiring the
device

The source L & N must be taken AS A SET to either the top or bottom
SET of terminals.

The output L & N is from the other SET (top or bottom).

Splitting the sets will cause the exact symptoms you describe.

If that is the case, how do you propose I connect it up in light of
the following rccb terminal layout:

There is a neutral connection on the top of the rccb.
On the bottom there are two live terminal pins (which plug directly
into the CU busbar) and a neutral connection

The unit is a Crabtree split-load rccb part no 363/s100

What would you do?

Cheers

How are you getting two pins from the live busbar into one terminal on
the Rcd? I think we really need a photograph. to make sense of what
you have

On 1 Mar 2007 11:37:22 -0800, "cynic" mused:

On 1 Mar, 12:15, wrote:
Snippet from the rccb installation instructions:

1)The incoming cables to the rccb may be taken either to the top or
bottom set of terminals, dependant entirely on the ease of wiring the
device

The source L & N must be taken AS A SET to either the top or bottom
SET of terminals.

The output L & N is from the other SET (top or bottom).

Splitting the sets will cause the exact symptoms you describe.

If that is the case, how do you propose I connect it up in light of
the following rccb terminal layout:

There is a neutral connection on the top of the rccb.
On the bottom there are two live terminal pins (which plug directly
into the CU busbar) and a neutral connection

The unit is a Crabtree split-load rccb part no 363/s100

What would you do?

Cheers

How are you getting two pins from the live busbar into one terminal on
the Rcd? I think we really need a photograph. to make sense of what
you have

On the bottom of the RCD are two plug in pins. One takes the power
from the end of the non-RCD'd busbar and the other pin plugs into the
RCD protected busbar. The busbar is split behind the RCD.
--
Regards,
Stuart.

On 2 Mar, 17:43, Lurch wrote:
On 1 Mar 2007 11:37:22 -0800, "cynic" mused:





On 1 Mar, 12:15, wrote:
Snippet from the rccb installation instructions:

1)The incoming cables to the rccb may be taken either to the top or
bottom set of terminals, dependant entirely on the ease of wiring the
device

The source L & N must be taken AS A SET to either the top or bottom
SET of terminals.

The output L & N is from the other SET (top or bottom).

Splitting the sets will cause the exact symptoms you describe.

If that is the case, how do you propose I connect it up in light of
the following rccb terminal layout:

There is a neutral connection on the top of the rccb.
On the bottom there are two live terminal pins (which plug directly
into the CU busbar) and a neutral connection

The unit is a Crabtree split-load rccb part no 363/s100

What would you do?

Cheers

How are you getting two pins from the live busbar into one terminal on
the Rcd? I think we really need a photograph. to make sense of what
you have

On the bottom of the RCD are two plug in pins. One takes the power
from the end of the non-RCD'd busbar and the other pin plugs into the
RCD protected busbar. The busbar is split behind the RCD.
--
Regards,
Stuart.- Hide quoted text -

- Show quoted text -

I'm even more confused now. I thought it was the mains incoming time
delayed RCD which was tripping. In this case I would expect the L & N
meter tails to go into the top two 100mA RCD terminals. From the
bottom I'd expect there to be a Live connection to the L of the 30mA
RCD and a connection to the 100mA protected busbar section for
lighting and fixed equipment. The (other bottom terminal) Neutral
output from the 100mA RCD would connect to the input N of the 30mA RCD
and to the 100mA protected Neutral bar. The 30mA (fast) RCD would have
its own bit of busbar for socket outlets and similar together with its
own bit of Neutral bar for these associated circuits.
If two or maybe three 100mA RCDs are showing the same failure to trip
by their own test button it does point to either live or neutral
connections being to the "wrong" end of the RCD i.e. diagonally across
corner connected. This would not give a leakage path simulation by the
button but would give a trip by normal current flow.
We need pictures!

On 2 Mar 2007 23:04:21 -0800, "cynic" mused:

How are you getting two pins from the live busbar into one terminal on
the Rcd? I think we really need a photograph. to make sense of what
you have

On the bottom of the RCD are two plug in pins. One takes the power
from the end of the non-RCD'd busbar and the other pin plugs into the
RCD protected busbar. The busbar is split behind the RCD.
--
Regards,
Stuart.- Hide quoted text -

- Show quoted text -

I'm even more confused now. I thought it was the mains incoming time
delayed RCD which was tripping. In this case I would expect the L & N
meter tails to go into the top two 100mA RCD terminals. From the
bottom I'd expect there to be a Live connection to the L of the 30mA
RCD and a connection to the 100mA protected busbar section for
lighting and fixed equipment. The (other bottom terminal) Neutral
output from the 100mA RCD would connect to the input N of the 30mA RCD
and to the 100mA protected Neutral bar. The 30mA (fast) RCD would have
its own bit of busbar for socket outlets and similar together with its
own bit of Neutral bar for these associated circuits.
If two or maybe three 100mA RCDs are showing the same failure to trip
by their own test button it does point to either live or neutral
connections being to the "wrong" end of the RCD i.e. diagonally across
corner connected. This would not give a leakage path simulation by the
button but would give a trip by normal current flow.
We need pictures!

Yeah, actually, I'm confused now!

Pictures required.
--
Regards,
Stuart.

On 28 Feb, 17:08, wrote:
Cheers for the thoughts

I have removed the links so that N1, N2, and N3 are separated and
wired as per the tech diagram for this configuration.

Basically both rccb's get the common supply neutral (N1) into them and
they feed the separate neutrals (N2 and N3) out the other side.

I really am scratching over my head over this one, and am on 1st name
terms with Crabtree technical haha!

Cheers

Oldskool

Revisiting this post - are you saying that the two RCDs have the meter
tail neutral into them both in parallel but one Rcd (the 100mA one)
has the live meter tail feeding it and the output of the live side
goes to the 30mA RCD and the 100mA protected bus bar? If I've read you
right the 30mA protected circuits take the live current through the
100mA AND the 30mA RCDs but the neutral return current passes through
the 30mA and NOT the 100mA unit. This means there is bound to be an
imbalance in the 100mA RCD if any current is drawn through the 30mA
RCD protected circuits and the 100mA RCD will trip as soon as a load
is switched on. In short it aint wired up right!

Theunitis a Crabtree split-load rccb part no 363/s100

What would you do?

Well, I'd fix it using m skills as an electrician to test everything
and make 300% sure everything is actually the right polarity.

Simple really, but you haven't filled me with confidence so I'm
guessing you haven't been through and tested everything?
--
Regards,
Stuart.- Hide quoted text -

- Show quoted text -

Just an update on this for those interested.

The third rccb did actually work thus proving the previous two to be
at fault, which is a first indeed! (Live and learn eh? - Not to use
Crabtree again that is!)

Thanks for your contributions in trying to work this out. For the
posts questioning my abilities I know you can't assume knowledge
automatically, but believe me when I say that I did test and check
everything before running to this newsgroup as a last resort. It's
nice that some people actually took that as read...

On Wednesday, 28 February 2007 17:08:04 UTC, wrote:
Cheers for the thoughts

I have removed the links so that N1, N2, and N3 are separated and
wired as per the tech diagram for this configuration.

Basically both rccb's get the common supply neutral (N1) into them and
they feed the separate neutrals (N2 and N3) out the other side.

I really am scratching over my head over this one, and am on 1st name
terms with Crabtree technical haha!

Cheers
I am having exactly the same problem, wondered if you have solved it. Ive replaced the split rcd unit
But with no joy. My unit is split on a stack one above the other With the bottom rcd working perfectly.
The earth reading is 45 ohms well within the regs. All connections have been copied from a split none stacked board. Any help gratefully received.

Oldskool