Currently being driven nuts by the above... I have a split load CU. When
the RCD trips, it's only that which goes; ie none of the MCBs trips at
the same time which means there's not much for me to go on.

Question 1: if, for diagnostic purposes, I switch off each circuit in
turn by manually flipping its MCB, does that actually isolate the
circuits for the purpose of elimination? Or would I need to open the CU
and physically disconnect all the cables from each circuit in turn,
completely?

Question 2: what does the fact that no MCBs are tripping; and the trips
occur at apparently random intervals (4-5 times in the last day, with
interval of up to ~10 hours so far, and including an overnight trip; and
no problem with reinstating the RCD immediately) tell me about the
nature of the fault, if anything?

Thanks for any pointers!

--
David

On 06/08/2013 09:58, Lobster wrote:
Currently being driven nuts by the above... I have a split load CU. When
the RCD trips, it's only that which goes; ie none of the MCBs trips at
the same time which means there's not much for me to go on.

Question 1: if, for diagnostic purposes, I switch off each circuit in
turn by manually flipping its MCB, does that actually isolate the
circuits for the purpose of elimination? Or would I need to open the CU
and physically disconnect all the cables from each circuit in turn,
completely?

MCB should do it but the circuit will no longer be live so you need to
put the freezer on full bore for a while first (which might actually
demonstrate conclusively that it is the root cause).

It is fastest if you drop out half at a time:

11110000
11001100
10101010

It could be ambiguous if no trip occurs. You may have to repeat with the
other handed pattern so that you have three patterns that all cause a
failure. Then depending on which pattern(s) trip out try just the
appropriate failing circuit on its own.

Question 2: what does the fact that no MCBs are tripping; and the trips
occur at apparently random intervals (4-5 times in the last day, with
interval of up to ~10 hours so far, and including an overnight trip; and
no problem with reinstating the RCD immediately) tell me about the
nature of the fault, if anything?

Thanks for any pointers!

My money would probably be on cooker, fridge, freezer or similar.
Transient earth leakage fault as a motor starts or something like that.

--
Regards,
Martin Brown

In article ,
Lobster wrote:
Currently being driven nuts by the above... I have a split load CU. When
the RCD trips, it's only that which goes; ie none of the MCBs trips at
the same time which means there's not much for me to go on.

Question 1: if, for diagnostic purposes, I switch off each circuit in
turn by manually flipping its MCB, does that actually isolate the
circuits for the purpose of elimination? Or would I need to open the CU
and physically disconnect all the cables from each circuit in turn,
completely?

Question 2: what does the fact that no MCBs are tripping; and the trips
occur at apparently random intervals (4-5 times in the last day, with
interval of up to ~10 hours so far, and including an overnight trip; and
no problem with reinstating the RCD immediately) tell me about the
nature of the fault, if anything?

Thanks for any pointers!

The MCB will only trip on current overload. The RCD trip indicates a leak
to earth somewhere. This is frequently on things that have heating
elements, but they'd probably need to be switched on for the trip to occur.

But it could be water getting into a junction box somewhere. Do you have
any outdoor supplies?

--
From KT24

Using a RISC OS computer running v5.18

On Tue, 06 Aug 2013 09:58:03 +0100, Lobster wrote:

Question 1: if, for diagnostic purposes, I switch off each circuit in
turn by manually flipping its MCB, does that actually isolate the
circuits for the purpose of elimination?

Sort of. If the trips are being caused by a live earth leak then
switching off the MCB will give an indication that that circuit has a
problem. If the trips are from a neutral earth leak then switcging
off the MCB won't make any difference.

Question 2: what does the fact that no MCBs are tripping; and the trips
occur at apparently random intervals (4-5 times in the last day, with
interval of up to ~10 hours so far, and including an overnight trip; and
no problem with reinstating the RCD immediately) tell me about the
nature of the fault, if anything?

It's intermittent. B-) Others have pointed out likely appliances
but it could be down to rodent nibbled wiring...

--
Cheers
Dave.

On 06/08/2013 09:58, Lobster wrote:
Currently being driven nuts by the above... I have a split load CU. When
the RCD trips, it's only that which goes; ie none of the MCBs trips at
the same time which means there's not much for me to go on.

Question 1: if, for diagnostic purposes, I switch off each circuit in
turn by manually flipping its MCB, does that actually isolate the
circuits for the purpose of elimination?

It may prevent the trip, but you can't be certain, since switching off
the circuit leaves the neutral connected. If the cause of the problem
was say for example a neutral to earth short, then the trip could still
manifest.

Or would I need to open the CU
and physically disconnect all the cables from each circuit in turn,
completely?

That would ensure the circuit is isolated.

Question 2: what does the fact that no MCBs are tripping; and the trips
occur at apparently random intervals (4-5 times in the last day, with
interval of up to ~10 hours so far, and including an overnight trip; and
no problem with reinstating the RCD immediately) tell me about the
nature of the fault, if anything?

It tells you there is no associated overcurrent trip. It probably
indicates that you have high leakage that is "sensitising" the RCD (i.e.
using most of its trip current budget, and leaving it close to the point
of tripping), and hence it does not take much to put it over the edge.
Even transients on the mains that could originate outside of the house
may trigger the trip.

Thanks for any pointers!

Try he

http://wiki.diyfaq.org.uk/index.php?...Nuisance_trips


--
Cheers,

John.

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

In article ,
John Rumm writes:
It tells you there is no associated overcurrent trip. It probably
indicates that you have high leakage that is "sensitising" the RCD (i.e.
using most of its trip current budget, and leaving it close to the point
of tripping), and hence it does not take much to put it over the edge.
Even transients on the mains that could originate outside of the house
may trigger the trip.

My parents had a couple of trips recently, but knew it was a desk fan.
Fan is double insulated and all plastic case, so it can't generate
earth leaks. Eventually I opened the plug, and found a dead spider
nesting bwteen the live and (unused) earth connection.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

On Tue, 06 Aug 2013 09:58:03 +0100, Lobster
wrote:
Currently being driven nuts by the above... I have a split load CU. When
the RCD trips, it's only that which goes; ie none of the MCBs trips at
the same time which means there's not much for me to go on.

I has similar issues for years, which turned out to be a combination
of things:

1. An oven element, which had a leakage that was proportional to its
temperature, going up to around 10ma when it was red-hot. Measured by
breaking the earth wire out and measuring the current with a
multimeter on mA AC range. Cured by replacing the element.

2. An outside armoured cable with a low live/earth resistance when
wet. Discovered with a megger, cured by disconnecting the circuit.

3. A large number of switch-mode power supplies: household PCs,
router, NAS Etc, which all added up. Cured by replacing all the 32 amp
MCBs with RCBOs to give each ring it's own 30ma leakage budget.

On 06/08/2013 09:58, Lobster wrote:
Currently being driven nuts by the above... I have a split load CU. When
the RCD trips, it's only that which goes; ie none of the MCBs trips at
the same time which means there's not much for me to go on.

Question 1: if, for diagnostic purposes, I switch off each circuit in
turn by manually flipping its MCB, does that actually isolate the
circuits for the purpose of elimination? Or would I need to open the CU
and physically disconnect all the cables from each circuit in turn,
completely?

Question 2: what does the fact that no MCBs are tripping; and the trips
occur at apparently random intervals (4-5 times in the last day, with
interval of up to ~10 hours so far, and including an overnight trip; and
no problem with reinstating the RCD immediately) tell me about the
nature of the fault, if anything?

Thanks for any pointers!

Could be anything, but my first thought would be to check anything with
a heating element.

Over the years we've had it with the cooker, washing machine, dishwasher
and iron, but nothing else.

If your fridge/freezer is a frost free one, it'll have a heater too.

SteveW

On Tue, 06 Aug 2013 16:59:00 +0100, SteveW wrote:

On 06/08/2013 09:58, Lobster wrote:
Currently being driven nuts by the above... I have a split load CU.
When the RCD trips, it's only that which goes; ie none of the MCBs
trips at the same time which means there's not much for me to go on.

Question 1: if, for diagnostic purposes, I switch off each circuit in
turn by manually flipping its MCB, does that actually isolate the
circuits for the purpose of elimination? Or would I need to open the CU
and physically disconnect all the cables from each circuit in turn,
completely?

Question 2: what does the fact that no MCBs are tripping; and the trips
occur at apparently random intervals (4-5 times in the last day, with
interval of up to ~10 hours so far, and including an overnight trip;
and no problem with reinstating the RCD immediately) tell me about the
nature of the fault, if anything?

Thanks for any pointers!

Could be anything, but my first thought would be to check anything with
a heating element.

Over the years we've had it with the cooker, washing machine, dishwasher
and iron, but nothing else.

And an immersion heater if the OP has one.

--
Use the BIG mirror service in the UK: http://www.mirrorservice.org
My posts (including this one) are my copyright and if @diy_forums on
Twitter wish to tweet them they can pay me £30 a post
*lightning surge protection* - a w_tom conductor

On 06/08/2013 15:53, Caecilius wrote:

2. An outside armoured cable with a low live/earth resistance when
wet. Discovered with a megger, cured by disconnecting the circuit.

We started getting occasional RCD trips - every one being at at 10
o'clock at night. This was precisely when the time-switch for our garden
pond pump switched off (it's a 240v pump connected by 10m or so SWA cable).

Now I leave it running 24/7 (better for the external filter, apparently)
and no more problems. So it was either the time-switch or some weird
induction effect between earth and the armour wires when the voltage was
switched off.


--
Reentrant

On 06/08/2013 09:58, Lobster wrote:
Currently being driven nuts by the above... I have a split load CU.
When the RCD trips, it's only that which goes; ie none of the MCBs
trips at the same time which means there's not much for me to go on.

Question 1: if, for diagnostic purposes, I switch off each circuit in
turn by manually flipping its MCB, does that actually isolate the
circuits for the purpose of elimination? Or would I need to open the
CU and physically disconnect all the cables from each circuit in
turn, completely?

Question 2: what does the fact that no MCBs are tripping; and the
trips occur at apparently random intervals (4-5 times in the last
day, with interval of up to ~10 hours so far, and including an
overnight trip; and no problem with reinstating the RCD immediately)
tell me about the nature of the fault, if anything?

Thanks for any pointers!

Thanks for all the replies. It hasn't 'popped' since 5 am today (it's
now 9:30 pm so hopefully whatever it was has gone away... I'm suspecting
it might have been cat pee actually; no evidence but we certainly have a
problem here that way

--
David

3. A large number of switch-mode power supplies: household PCs,
router, NAS Etc, which all added up. Cured by replacing all the 32 amp
MCBs with RCBOs to give each ring it's own 30ma leakage budget.


Seconded. my old CU was a split load job, with 4 MCBs on a 30mA RCD
feeding a cooker, two ring mains and an immersion. The other half of the
CU was two MCBs feeding two lighting circuits.

Whenever I started two PCs or more at the same time, that would trip the
RCD. The trouble was that 30mA leakage current budget was spread across
four circuits.

I then got the CU changed for one that had RCBOs only and i split
several circuits up into smaller circuits and added new circuits. This I
went from 6 to 13 circuits, all on RCBO's

I also added high integrity as well, so the smoke dets, CO dets and
intruder alarm are on their own RCBO, the outside sockets are on their
own RCBO and the outside lights are on their own RCBO. That way anything
happening outside does not affect the inside.

The boiler is also on its own RCBO so reducing the risk of the house
freezing over if a different circuit develops a fault.

I've not had a single trip since.

although RCBOs are more expensive, its worth every penny from the
hassle/inconvenience/ease of fault finding point of view.

Lobster wrote:
Currently being driven nuts by the above... I have a split load CU. When
the RCD trips, it's only that which goes; ie none of the MCBs trips at
the same time which means there's not much for me to go on.

Question 1: if, for diagnostic purposes, I switch off each circuit in
turn by manually flipping its MCB, does that actually isolate the
circuits for the purpose of elimination? Or would I need to open the CU
and physically disconnect all the cables from each circuit in turn,
completely?

Question 2: what does the fact that no MCBs are tripping; and the trips
occur at apparently random intervals (4-5 times in the last day, with
interval of up to ~10 hours so far, and including an overnight trip; and
no problem with reinstating the RCD immediately) tell me about the
nature of the fault, if anything?

Thanks for any pointers!

Kettle or some other appliance kept near the sink.

On Wednesday, 7 August 2013 03:39:55 UTC+1, F Murtz wrote:

Kettle or some other appliance kept near the sink.

Mine tripped yesterday due to a loose raisin from a teacake becoming stuck between the toaster element and the case. Happened twice (different raisins).

On Wed, 07 Aug 2013 01:24:54 -0700, David wrote:

On Wednesday, 7 August 2013 03:39:55 UTC+1, F Murtz wrote:

Kettle or some other appliance kept near the sink.

Mine tripped yesterday due to a loose raisin from a teacake becoming
stuck between the toaster element and the case. Happened twice
(different raisins).

At least it wasn't an excessively large currant.

--
Use the BIG mirror service in the UK: http://www.mirrorservice.org
My posts (including this one) are my copyright and if @diy_forums on
Twitter wish to tweet them they can pay me £30 a post
*lightning surge protection* - a w_tom conductor

On 07/08/2013 10:26, Bob Eager wrote:
On Wed, 07 Aug 2013 01:24:54 -0700, David wrote:

On Wednesday, 7 August 2013 03:39:55 UTC+1, F Murtz wrote:

Kettle or some other appliance kept near the sink.

Mine tripped yesterday due to a loose raisin from a teacake becoming
stuck between the toaster element and the case. Happened twice
(different raisins).

At least it wasn't an excessively large currant.

fx applause



--
Cheers,

John.

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

On 7 Aug 2013 09:26:39 GMT, Bob Eager wrote:

Mine tripped yesterday due to a loose raisin from a teacake
becoming
stuck between the toaster element and the case. Happened twice
(different raisins).

At least it wasn't an excessively large currant.

Or a large fly and excessively currant.

--
Cheers
Dave.