The house suddenly lost power a couple of days ago and on checking the
circuit breaker box I found the one controlling the immersion heater
had tripped. But that is not switched on (it hardly ever is), so how
could a leak be detected by the circuit breaker?

After resetting that breaker there has been no re-occurrence, but with
a two week holiday imminent I'm nervous that it may happen again. It's
no big deal to return to a house with maybe some of my
electronically-controlled devices switched on (lights, radio, TV,
garden waterfall, etc), as occasionally happens due to storm
lightning, or a widespread power failure, but the fridge and freezer
would be a major issue.

The immersion heater cable from the heater coil on top of the hot
water tank in the airing cupboard goes directly to the switch on the
wall, with no intervening mains plug/socket. So presumably, to get an
ohm reading on this unit to test for leakage, I have to first switch
off at the breaker box, remove the switch panel in the airing
cupboard, unscrew a connection, and work from there?

Any practical advice would be much appreciated please.

--
Terry, West Sussex, UK

"Terry Pinnell" wrote in message
...
The house suddenly lost power a couple of days ago and on checking the
circuit breaker box I found the one controlling the immersion heater
had tripped. But that is not switched on (it hardly ever is), so how
could a leak be detected by the circuit breaker?

After resetting that breaker there has been no re-occurrence, but with
a two week holiday imminent I'm nervous that it may happen again. It's
no big deal to return to a house with maybe some of my
electronically-controlled devices switched on (lights, radio, TV,
garden waterfall, etc), as occasionally happens due to storm
lightning, or a widespread power failure, but the fridge and freezer
would be a major issue.

The immersion heater cable from the heater coil on top of the hot
water tank in the airing cupboard goes directly to the switch on the
wall, with no intervening mains plug/socket. So presumably, to get an
ohm reading on this unit to test for leakage, I have to first switch
off at the breaker box, remove the switch panel in the airing
cupboard, unscrew a connection, and work from there?

Any practical advice would be much appreciated please.

--
Terry, West Sussex, UK

The immersion heater switch is normally a double pole type, so if it's
switched off, the heater element is completely isolated anyway, so cannot be
responsible for for its feed MCB detecting leakage. When you say that your
house had lost all power, was the actual consumer unit breaker tripped, as
well as the immersion heater MCB, leading you to believe that an immersion
heater failure had tripped both ?

Arfa

In article ,
Terry Pinnell wrote:
The house suddenly lost power a couple of days ago and on checking the
circuit breaker box I found the one controlling the immersion heater
had tripped. But that is not switched on (it hardly ever is), so how
could a leak be detected by the circuit breaker?

If the whole house tripped out you've probably got one RCD for
everything. This works by looking for an imbalance in current flow
between the line and neutral - if everything is ok the current in each of
these will be identical. If, however, either of those conductors has a
fault to earth - doesn't have to be a short circuit - the device will
trip. And it can happen with a single pole switched device even when it's
off.

Mineral insulated heating elements like immersions and some oven elements
are notorious for this sort of fault - you get a slight leakage to earth,
but it still works ok. And it's unlikely to be the same on both legs so
upsets the RCD which trips.

These days most recommend a split load CU where only some circuits are
RCD protected, and things like the immersion and cooker - which are hard
wired so no safety implication there - are fed from the non RCD side.

--
*Many hamsters only blink one eye at a time *

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

Terry Pinnell wrote in message
...
The house suddenly lost power a couple of days ago and on checking the
circuit breaker box I found the one controlling the immersion heater
had tripped. But that is not switched on (it hardly ever is), so how
could a leak be detected by the circuit breaker?

After resetting that breaker there has been no re-occurrence, but with
a two week holiday imminent I'm nervous that it may happen again. It's
no big deal to return to a house with maybe some of my
electronically-controlled devices switched on (lights, radio, TV,
garden waterfall, etc), as occasionally happens due to storm
lightning, or a widespread power failure, but the fridge and freezer
would be a major issue.

The immersion heater cable from the heater coil on top of the hot
water tank in the airing cupboard goes directly to the switch on the
wall, with no intervening mains plug/socket. So presumably, to get an
ohm reading on this unit to test for leakage, I have to first switch
off at the breaker box, remove the switch panel in the airing
cupboard, unscrew a connection, and work from there?

Any practical advice would be much appreciated please.

--
Terry, West Sussex, UK

Tripped MCB or RCCD/ELCB device?

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

"N Cook" wrote:

Terry Pinnell wrote in message
.. .
The house suddenly lost power a couple of days ago and on checking the
circuit breaker box I found the one controlling the immersion heater
had tripped. But that is not switched on (it hardly ever is), so how
could a leak be detected by the circuit breaker?

After resetting that breaker there has been no re-occurrence, but with
a two week holiday imminent I'm nervous that it may happen again. It's
no big deal to return to a house with maybe some of my
electronically-controlled devices switched on (lights, radio, TV,
garden waterfall, etc), as occasionally happens due to storm
lightning, or a widespread power failure, but the fridge and freezer
would be a major issue.

The immersion heater cable from the heater coil on top of the hot
water tank in the airing cupboard goes directly to the switch on the
wall, with no intervening mains plug/socket. So presumably, to get an
ohm reading on this unit to test for leakage, I have to first switch
off at the breaker box, remove the switch panel in the airing
cupboard, unscrew a connection, and work from there?

Any practical advice would be much appreciated please.

--
Terry, West Sussex, UK

Tripped MCB or RCCD/ELCB device?

Thanks for those prompt and helpful replies. I'm responding to the
requests for more info:

The unit is a 'Crabtree', and carries a label '8A/30mA'.

It has two sections:

CIRCUIT BREAKERS:
-----------------
1. Upstairs lights: 2 shaver-sockets in bathrooms; outside security
light (from loft extension)

2. Downstairs lights: hall, kitchen ceiling & under cupboard,
downstairs toilet (and fan), cupboard under stairs (and alarm)

3. Downstairs lights: lounge, dining room

4. Transformer by board (This is an add-on of my own, as part of a
gadget to detect when the front door bell was pressed, to buzz a
garden extension. Not a possible culprit IMO.)

5. Spare

RCD PROTECTED CIRCUITS:
-----------------------

1. Immersion heater. (This is the one that tripped.)

2. Sockets (radial): My office. Too many items to list here.

3. Sockets (ring): Downstairs except kitchen (5); Garage (1); Upstairs
except main bedroom (6)

4. Sockets (ring): Main bedroom including spurs (1): Hall (1); Kitchen
(6), Utility (3), upstairs bedroom

5. Cooker and 1 socket by cooker switch.

I also have two other RCD units
- In garage mains socket, protecting garden and workshop circuits
- In lounge mains socket, protecting garden pond submersed pump

After the failure I thought *all* power was lost. But now I can't be
100% sure whether I had the lights on, and I don't recall checking
them. Certainly things like fridge, microwave, etc were off.

The only switch I reset in the Crabtree unit was the RCD one
controlling the immersion heater.

I haven't unscrewed the immersion heater wall switch yet, so can't
confirm whether it's single or double pole. But doesn't the fact that
this RCD was tripped mean that it *must* be single pole, with a leak?

Hope this helps further diagnosis.

--
Terry, West Sussex, UK

Terry Pinnell wrote in message
...
"N Cook" wrote:

Terry Pinnell wrote in message
.. .
The house suddenly lost power a couple of days ago and on checking the
circuit breaker box I found the one controlling the immersion heater
had tripped. But that is not switched on (it hardly ever is), so how
could a leak be detected by the circuit breaker?

After resetting that breaker there has been no re-occurrence, but with
a two week holiday imminent I'm nervous that it may happen again. It's
no big deal to return to a house with maybe some of my
electronically-controlled devices switched on (lights, radio, TV,
garden waterfall, etc), as occasionally happens due to storm
lightning, or a widespread power failure, but the fridge and freezer
would be a major issue.

The immersion heater cable from the heater coil on top of the hot
water tank in the airing cupboard goes directly to the switch on the
wall, with no intervening mains plug/socket. So presumably, to get an
ohm reading on this unit to test for leakage, I have to first switch
off at the breaker box, remove the switch panel in the airing
cupboard, unscrew a connection, and work from there?

Any practical advice would be much appreciated please.

--
Terry, West Sussex, UK

Tripped MCB or RCCD/ELCB device?

Thanks for those prompt and helpful replies. I'm responding to the
requests for more info:

The unit is a 'Crabtree', and carries a label '8A/30mA'.

It has two sections:

CIRCUIT BREAKERS:
-----------------
1. Upstairs lights: 2 shaver-sockets in bathrooms; outside security
light (from loft extension)

2. Downstairs lights: hall, kitchen ceiling & under cupboard,
downstairs toilet (and fan), cupboard under stairs (and alarm)

3. Downstairs lights: lounge, dining room

4. Transformer by board (This is an add-on of my own, as part of a
gadget to detect when the front door bell was pressed, to buzz a
garden extension. Not a possible culprit IMO.)

5. Spare

RCD PROTECTED CIRCUITS:
-----------------------

1. Immersion heater. (This is the one that tripped.)

2. Sockets (radial): My office. Too many items to list here.

3. Sockets (ring): Downstairs except kitchen (5); Garage (1); Upstairs
except main bedroom (6)

4. Sockets (ring): Main bedroom including spurs (1): Hall (1); Kitchen
(6), Utility (3), upstairs bedroom

5. Cooker and 1 socket by cooker switch.

I also have two other RCD units
- In garage mains socket, protecting garden and workshop circuits
- In lounge mains socket, protecting garden pond submersed pump

After the failure I thought *all* power was lost. But now I can't be
100% sure whether I had the lights on, and I don't recall checking
them. Certainly things like fridge, microwave, etc were off.

The only switch I reset in the Crabtree unit was the RCD one
controlling the immersion heater.

I haven't unscrewed the immersion heater wall switch yet, so can't
confirm whether it's single or double pole. But doesn't the fact that
this RCD was tripped mean that it *must* be single pole, with a leak?

Hope this helps further diagnosis.

--
Terry, West Sussex, UK

Probably just that that RCD trip is more sensitive to unbalanced inductive
load on another circuit, usually the motor of a washing machine but
theoretically could be due to a neighbour using an arc welder, anything else
very inductive, distant lightening strike etc. If definitely no problem with
the immersion wiring then change the RCD.

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

In article ,
Terry Pinnell wrote:
The unit is a 'Crabtree', and carries a label '8A/30mA'.

It has two sections:

CIRCUIT BREAKERS:
-----------------
1. Upstairs lights: 2 shaver-sockets in bathrooms; outside security
light (from loft extension)

2. Downstairs lights: hall, kitchen ceiling & under cupboard,
downstairs toilet (and fan), cupboard under stairs (and alarm)

3. Downstairs lights: lounge, dining room

4. Transformer by board (This is an add-on of my own, as part of a
gadget to detect when the front door bell was pressed, to buzz a
garden extension. Not a possible culprit IMO.)

5. Spare

RCD PROTECTED CIRCUITS:
-----------------------

1. Immersion heater. (This is the one that tripped.)

Because of nuisance tripping this would normally go on the non RCD side.

2. Sockets (radial): My office. Too many items to list here.

3. Sockets (ring): Downstairs except kitchen (5); Garage (1); Upstairs
except main bedroom (6)

4. Sockets (ring): Main bedroom including spurs (1): Hall (1); Kitchen
(6), Utility (3), upstairs bedroom

5. Cooker and 1 socket by cooker switch.

Likewise this - but remove the socket.

I also have two other RCD units
- In garage mains socket, protecting garden and workshop circuits
- In lounge mains socket, protecting garden pond submersed pump

After the failure I thought *all* power was lost. But now I can't be
100% sure whether I had the lights on, and I don't recall checking
them. Certainly things like fridge, microwave, etc were off.

The only way everything could go off with a split load CU is if the main
fuse blows. That's the 'company' one before the meter.

The only switch I reset in the Crabtree unit was the RCD one
controlling the immersion heater.

You mean the RCD controlling that side of the board - not the MCB for the
immersion?

I haven't unscrewed the immersion heater wall switch yet, so can't
confirm whether it's single or double pole. But doesn't the fact that
this RCD was tripped mean that it *must* be single pole, with a leak?

Could be anything on that side of the CU.

Hope this helps further diagnosis.

--
*No I haven't stolen it , I'm just a **** driver*

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

"Dave Plowman (News)" wrote in message
...
In article ,
Terry Pinnell wrote:
The unit is a 'Crabtree', and carries a label '8A/30mA'.

It has two sections:

CIRCUIT BREAKERS:
-----------------
1. Upstairs lights: 2 shaver-sockets in bathrooms; outside security
light (from loft extension)

2. Downstairs lights: hall, kitchen ceiling & under cupboard,
downstairs toilet (and fan), cupboard under stairs (and alarm)

3. Downstairs lights: lounge, dining room

4. Transformer by board (This is an add-on of my own, as part of a
gadget to detect when the front door bell was pressed, to buzz a
garden extension. Not a possible culprit IMO.)

5. Spare

RCD PROTECTED CIRCUITS:
-----------------------

1. Immersion heater. (This is the one that tripped.)

Because of nuisance tripping this would normally go on the non RCD side.

2. Sockets (radial): My office. Too many items to list here.

3. Sockets (ring): Downstairs except kitchen (5); Garage (1); Upstairs
except main bedroom (6)

4. Sockets (ring): Main bedroom including spurs (1): Hall (1); Kitchen
(6), Utility (3), upstairs bedroom

5. Cooker and 1 socket by cooker switch.

Likewise this - but remove the socket.

I also have two other RCD units
- In garage mains socket, protecting garden and workshop circuits
- In lounge mains socket, protecting garden pond submersed pump

After the failure I thought *all* power was lost. But now I can't be
100% sure whether I had the lights on, and I don't recall checking
them. Certainly things like fridge, microwave, etc were off.

The only way everything could go off with a split load CU is if the main
fuse blows. That's the 'company' one before the meter.

The only switch I reset in the Crabtree unit was the RCD one
controlling the immersion heater.

You mean the RCD controlling that side of the board - not the MCB for the
immersion?

I haven't unscrewed the immersion heater wall switch yet, so can't
confirm whether it's single or double pole. But doesn't the fact that
this RCD was tripped mean that it *must* be single pole, with a leak?

Could be anything on that side of the CU.

Hope this helps further diagnosis.


All agreed. If it was only the MCB for the immersion circuit that had
tripped, this could not affect all the ring and radial power circuits ( and
possibly the lights too ! ) unless there is something seriously wrong with
the way it's all wired. You must be talking main RCD trip for that side, as
Dave says ? As far as the immersion switch goes, it could indicate single
pole and a leak for the MCB on that circuit tripping, but in order for all
the other stuff to have gone out as well, there must have been something
else tripped on the feed to that side's fuse bus.

Arfa

Terry Pinnell wrote:



Thanks for those prompt and helpful replies. I'm responding to the
requests for more info:

The unit is a 'Crabtree', and carries a label '8A/30mA'.


Is this the SB6000 series by any chance, or at least that series/vintage?
(20 years old or more I'd think now!) There should be a label somewhere on
the fascia.

If so, these are known to get 'twitchy' as they age, the breakers trip for
no apparent reason and the only cure is replacement. However, I'm not sure
the individual breakers are available now, you may have to replace the
whole distribution box if it becomes troublesome- like I did!

If the problem reoccurs regularly it would be wise to consult an electrician
and get a quote. If it's just the immersion heater circuit though, you may
choose to just live with the minor inconvenience if it isn't regularly used
and spare breakers can't be sourced- changing the whole distribution box
isn't cheap!

Morse

Morse wrote:

Terry Pinnell wrote:



Thanks for those prompt and helpful replies. I'm responding to the
requests for more info:

The unit is a 'Crabtree', and carries a label '8A/30mA'.


Is this the SB6000 series by any chance, or at least that series/vintage?
(20 years old or more I'd think now!) There should be a label somewhere on
the fascia.

If so, these are known to get 'twitchy' as they age, the breakers trip for
no apparent reason and the only cure is replacement. However, I'm not sure
the individual breakers are available now, you may have to replace the
whole distribution box if it becomes troublesome- like I did!

If the problem reoccurs regularly it would be wise to consult an electrician
and get a quote. If it's just the immersion heater circuit though, you may
choose to just live with the minor inconvenience if it isn't regularly used
and spare breakers can't be sourced- changing the whole distribution box
isn't cheap!

Morse

Thanks for the follow-ups. I'm going to have to do some more careful
reading, maybe starting here
http://wiki.diyfaq.org.uk/index.php?title=RCD
as I don't really understand the basics, and hence some of the advice
given. Meanwhile, beginning to regret switching from my old fuse-based
unit a year or so ago!

The Crabtree is a modern modular unit, but so far I've not found its
spec. I'll do so as soon as possible and report back.

--
Terry, West Sussex, UK

Terry Pinnell wrote in message
...
Morse wrote:

Terry Pinnell wrote:



Thanks for those prompt and helpful replies. I'm responding to the
requests for more info:

The unit is a 'Crabtree', and carries a label '8A/30mA'.


Is this the SB6000 series by any chance, or at least that series/vintage?
(20 years old or more I'd think now!) There should be a label somewhere
on
the fascia.

If so, these are known to get 'twitchy' as they age, the breakers trip
for
no apparent reason and the only cure is replacement. However, I'm not
sure
the individual breakers are available now, you may have to replace the
whole distribution box if it becomes troublesome- like I did!

If the problem reoccurs regularly it would be wise to consult an
electrician
and get a quote. If it's just the immersion heater circuit though, you
may
choose to just live with the minor inconvenience if it isn't regularly
used
and spare breakers can't be sourced- changing the whole distribution box
isn't cheap!

Morse

Thanks for the follow-ups. I'm going to have to do some more careful
reading, maybe starting here
http://wiki.diyfaq.org.uk/index.php?title=RCD
as I don't really understand the basics, and hence some of the advice
given. Meanwhile, beginning to regret switching from my old fuse-based
unit a year or so ago!

The Crabtree is a modern modular unit, but so far I've not found its
spec. I'll do so as soon as possible and report back.

--
Terry, West Sussex, UK


Is the local supply into your house by overhead wire or underground feed.?
Do neighbours on the same phase (their lights go off with yours, about every
1 in 3 houses if there is a local sub-station/transformer problem/power cut)
have similar problems ?

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

Terry Pinnell wrote:

Morse wrote:

Terry Pinnell wrote:



Thanks for those prompt and helpful replies. I'm responding to the
requests for more info:

The unit is a 'Crabtree', and carries a label '8A/30mA'.


Is this the SB6000 series by any chance, or at least that series/vintage?
(20 years old or more I'd think now!) There should be a label somewhere on
the fascia.

If so, these are known to get 'twitchy' as they age, the breakers trip for
no apparent reason and the only cure is replacement. However, I'm not sure
the individual breakers are available now, you may have to replace the
whole distribution box if it becomes troublesome- like I did!

If the problem reoccurs regularly it would be wise to consult an electrician
and get a quote. If it's just the immersion heater circuit though, you may
choose to just live with the minor inconvenience if it isn't regularly used
and spare breakers can't be sourced- changing the whole distribution box
isn't cheap!

Morse

Thanks for the follow-ups. I'm going to have to do some more careful
reading, maybe starting here
http://wiki.diyfaq.org.uk/index.php?title=RCD
as I don't really understand the basics, and hence some of the advice
given. Meanwhile, beginning to regret switching from my old fuse-based
unit a year or so ago!

The Crabtree is a modern modular unit, but so far I've not found its
spec. I'll do so as soon as possible and report back.

I've also taken a photo and labeled it as per my previous post.
http://www.terrypin.dial.pipex.com/Images/CU-1.jpg

(BTW, MCB #5 on the RCD side is disconnected.)

Note that I realise that the RCD controls electricity to all the MCBs
on the RCD side of the unit (not just the immersion heater). But I
think I was correct in my recollection that the only switch I reset in
the Crabtree unit was the RCD one.

--
Terry, West Sussex, UK

In article ,
Terry Pinnell wrote:
Thanks for the follow-ups. I'm going to have to do some more careful
reading, maybe starting here
http://wiki.diyfaq.org.uk/index.php?title=RCD
as I don't really understand the basics, and hence some of the advice
given. Meanwhile, beginning to regret switching from my old fuse-based
unit a year or so ago!

Was the work done by a qualified electrician? It just seems strange to me
that the immersion is on the RCD side. And since you said it replaced a
fuse based unit was the house re-wired at the same time?

The Crabtree is a modern modular unit, but so far I've not found its
spec. I'll do so as soon as possible and report back.

If it's a current Starbreaker unit I've fitted several including my own
and they've been fine.

--
*Tell me to 'stuff it' - I'm a taxidermist.

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

This puzzle now has another twist. I decided to do some methodical
leakage tests. My intention was to introduce a leakage from the live
connection of the circuit under test to a convenient earth, and
observe what tripped. That would at least confirm that I understood
what behaviour I was *supposed* to get from my Crabtree StarBreaker
CU. I used a couple of robust 15k resistors in parallel, theoretically
giving me a leakage around 32 mA (in my UK 240 V circuits).

I decided to start with an unimportant circuit, which also had an
extra RCD unit over and above the main CU. This is a double socket RCD
in the garage, fed from #3 on the Main Switch (non-RCD) side of the
CU. As expected, momentarily connecting this leakage current
immediately tripped the garage RCD. However, to my surprise, maybe 1-2
seconds later (with the leakage removed), the *main* switch on the CU
was tripped. So my PC and various household devices and clocks went
down despite my cunning plan ;-)

I'd not have expected this to happen, so could someone offer a
possible explanation please? Does it offer more insight into the odd
behaviour already reported?

In case it helps, the electrician's scrawled installation notes record
trip times of 18/19 ms for all the RCD circuits, and 7 ms for the
external garage RCD unit. There are various other columns like 'Loop
Impedance', 'CPC-CPC ohms', 'Ph-Ph ohms', 'R1+R2 or R2 ohms'; they
mean nothing to me but please let me know if they could help the
diagnosis.

--
Terry, West Sussex, UK

Terry Pinnell wrote:

This puzzle now has another twist. I decided to do some methodical
leakage tests. My intention was to introduce a leakage from the live
connection of the circuit under test to a convenient earth, and
observe what tripped. That would at least confirm that I understood
what behaviour I was *supposed* to get from my Crabtree StarBreaker
CU. I used a couple of robust 15k resistors in parallel, theoretically
giving me a leakage around 32 mA (in my UK 240 V circuits).

I decided to start with an unimportant circuit, which also had an
extra RCD unit over and above the main CU. This is a double socket RCD
in the garage, fed from #3 on the Main Switch (non-RCD) side of the
CU. As expected, momentarily connecting this leakage current
immediately tripped the garage RCD. However, to my surprise, maybe 1-2
seconds later (with the leakage removed), the *main* switch on the CU
was tripped. So my PC and various household devices and clocks went
down despite my cunning plan ;-)

I'd not have expected this to happen, so could someone offer a
possible explanation please? Does it offer more insight into the odd
behaviour already reported?

In case it helps, the electrician's scrawled installation notes record
trip times of 18/19 ms for all the RCD circuits, and 7 ms for the
external garage RCD unit. There are various other columns like 'Loop
Impedance', 'CPC-CPC ohms', 'Ph-Ph ohms', 'R1+R2 or R2 ohms'; they
mean nothing to me but please let me know if they could help the
diagnosis.

Pondering this over a coffee shortly after hitting Send, I realised
that I was wrong to imply the devices on this circuit were
insignificant. I left all the devices in place when I applied the
leakage. Amongst other things, I have an ancient large DC power supply
in my shed/workshop (30A), permanently connected to provide automatic
garden lighting at dusk. I'm wondering if perhaps some sort of
inductive effect might be responsible? Could the sudden removal of
power from that and other lower-rated transformers have had the effect
observed? If so, my starting choice was poor, and I'll try another
circuit. Or maybe disconnect the two plugs from the garage RCD unit.

--
Terry, West Sussex, UK

"Terry Pinnell" wrote in message
...
Terry Pinnell wrote:

This puzzle now has another twist. I decided to do some methodical
leakage tests. My intention was to introduce a leakage from the live
connection of the circuit under test to a convenient earth, and
observe what tripped. That would at least confirm that I understood
what behaviour I was *supposed* to get from my Crabtree StarBreaker
CU. I used a couple of robust 15k resistors in parallel, theoretically
giving me a leakage around 32 mA (in my UK 240 V circuits).

I decided to start with an unimportant circuit, which also had an
extra RCD unit over and above the main CU. This is a double socket RCD
in the garage, fed from #3 on the Main Switch (non-RCD) side of the
CU. As expected, momentarily connecting this leakage current
immediately tripped the garage RCD. However, to my surprise, maybe 1-2
seconds later (with the leakage removed), the *main* switch on the CU
was tripped. So my PC and various household devices and clocks went
down despite my cunning plan ;-)

I'd not have expected this to happen, so could someone offer a
possible explanation please? Does it offer more insight into the odd
behaviour already reported?

In case it helps, the electrician's scrawled installation notes record
trip times of 18/19 ms for all the RCD circuits, and 7 ms for the
external garage RCD unit. There are various other columns like 'Loop
Impedance', 'CPC-CPC ohms', 'Ph-Ph ohms', 'R1+R2 or R2 ohms'; they
mean nothing to me but please let me know if they could help the
diagnosis.

Pondering this over a coffee shortly after hitting Send, I realised
that I was wrong to imply the devices on this circuit were
insignificant. I left all the devices in place when I applied the
leakage. Amongst other things, I have an ancient large DC power supply
in my shed/workshop (30A), permanently connected to provide automatic
garden lighting at dusk. I'm wondering if perhaps some sort of
inductive effect might be responsible? Could the sudden removal of
power from that and other lower-rated transformers have had the effect
observed? If so, my starting choice was poor, and I'll try another
circuit. Or maybe disconnect the two plugs from the garage RCD unit.


Ahhh ... Very possibly ... I'll still ask my neighbour, though ( see my
other reply )

Arfa

On Tue, 10 Jul 2007 09:30:24 +0100, Terry Pinnell
wrote:

Terry Pinnell wrote:

This puzzle now has another twist. I decided to do some methodical
leakage tests. My intention was to introduce a leakage from the live
connection of the circuit under test to a convenient earth, and
observe what tripped. That would at least confirm that I understood
what behaviour I was *supposed* to get from my Crabtree StarBreaker
CU. I used a couple of robust 15k resistors in parallel, theoretically
giving me a leakage around 32 mA (in my UK 240 V circuits).

I decided to start with an unimportant circuit, which also had an
extra RCD unit over and above the main CU. This is a double socket RCD
in the garage, fed from #3 on the Main Switch (non-RCD) side of the
CU. As expected, momentarily connecting this leakage current
immediately tripped the garage RCD. However, to my surprise, maybe 1-2
seconds later (with the leakage removed), the *main* switch on the CU
was tripped. So my PC and various household devices and clocks went
down despite my cunning plan ;-)

I'd not have expected this to happen, so could someone offer a
possible explanation please? Does it offer more insight into the odd
behaviour already reported?

In case it helps, the electrician's scrawled installation notes record
trip times of 18/19 ms for all the RCD circuits, and 7 ms for the
external garage RCD unit. There are various other columns like 'Loop
Impedance', 'CPC-CPC ohms', 'Ph-Ph ohms', 'R1+R2 or R2 ohms'; they
mean nothing to me but please let me know if they could help the
diagnosis.

Pondering this over a coffee shortly after hitting Send, I realised
that I was wrong to imply the devices on this circuit were
insignificant. I left all the devices in place when I applied the
leakage. Amongst other things, I have an ancient large DC power supply
in my shed/workshop (30A), permanently connected to provide automatic
garden lighting at dusk. I'm wondering if perhaps some sort of
inductive effect might be responsible? Could the sudden removal of
power from that and other lower-rated transformers have had the effect
observed? If so, my starting choice was poor, and I'll try another
circuit. Or maybe disconnect the two plugs from the garage RCD unit.


Can you confirm that it was the main switch on the far left that
tripped or was it the RCD in the middle? I suspect that the socket
outlet only disconnects the live conductor and not the neutral, very
common, hence your leakage providing a link between N and E possibly
combined with the power supply tripping the RCD. The main switch on
the left is purely a switch and contains no over current or RCD
device, if that has turned itself off then someone's playing tricks or
it needs to be changed, however I have never come across that 15
years.

On you main board the switch on the far left controls everything up to
the RCD (RCD included), and the RCD everything after that. I my
experience it's usually caused by an appliance somewhere, washing
machine, cooker and anything plugged in outside seem to be the popular
ones. Other less likely causes are loose contacts in a socket, and
mice.

Wait and see if it happens again, and note down what was on when it
went. If it seems to be at random get a spark in and get him to do an
insulation test at 250v with live and neutral joined to earth with
everything connected. It's not accepted practice but it usually finds
the fault! In my mind nothing has happened that seems especially odd,
and other than doing a quick test of earth loop impedance and RCD trip
times for peace of mind, I wouldn't look any further and advise to
wait and see.

It's a shame you don't live in Herefordshire or I'd offer to pop round
and do a quick check for a cup of coffee!

Graham

Graham wrote:

On Tue, 10 Jul 2007 09:30:24 +0100, Terry Pinnell
wrote:

Terry Pinnell wrote:

This puzzle now has another twist. I decided to do some methodical
leakage tests. My intention was to introduce a leakage from the live
connection of the circuit under test to a convenient earth, and
observe what tripped. That would at least confirm that I understood
what behaviour I was *supposed* to get from my Crabtree StarBreaker
CU. I used a couple of robust 15k resistors in parallel, theoretically
giving me a leakage around 32 mA (in my UK 240 V circuits).

I decided to start with an unimportant circuit, which also had an
extra RCD unit over and above the main CU. This is a double socket RCD
in the garage, fed from #3 on the Main Switch (non-RCD) side of the
CU. As expected, momentarily connecting this leakage current
immediately tripped the garage RCD. However, to my surprise, maybe 1-2
seconds later (with the leakage removed), the *main* switch on the CU
was tripped. So my PC and various household devices and clocks went
down despite my cunning plan ;-)

I'd not have expected this to happen, so could someone offer a
possible explanation please? Does it offer more insight into the odd
behaviour already reported?

In case it helps, the electrician's scrawled installation notes record
trip times of 18/19 ms for all the RCD circuits, and 7 ms for the
external garage RCD unit. There are various other columns like 'Loop
Impedance', 'CPC-CPC ohms', 'Ph-Ph ohms', 'R1+R2 or R2 ohms'; they
mean nothing to me but please let me know if they could help the
diagnosis.

Pondering this over a coffee shortly after hitting Send, I realised
that I was wrong to imply the devices on this circuit were
insignificant. I left all the devices in place when I applied the
leakage. Amongst other things, I have an ancient large DC power supply
in my shed/workshop (30A), permanently connected to provide automatic
garden lighting at dusk. I'm wondering if perhaps some sort of
inductive effect might be responsible? Could the sudden removal of
power from that and other lower-rated transformers have had the effect
observed? If so, my starting choice was poor, and I'll try another
circuit. Or maybe disconnect the two plugs from the garage RCD unit.


Can you confirm that it was the main switch on the far left that
tripped or was it the RCD in the middle?

Thanks Graham, appreciate your reply. Yes, it was the RCD switch that
had opened.

I suspect that the socket
outlet only disconnects the live conductor and not the neutral, very
common, hence your leakage providing a link between N and E possibly
combined with the power supply tripping the RCD. The main switch on
the left is purely a switch and contains no over current or RCD
device, if that has turned itself off then someone's playing tricks or
it needs to be changed, however I have never come across that 15
years.

On you main board the switch on the far left controls everything up to
the RCD (RCD included), and the RCD everything after that. I my
experience it's usually caused by an appliance somewhere, washing
machine, cooker and anything plugged in outside seem to be the popular
ones. Other less likely causes are loose contacts in a socket, and
mice.

Wait and see if it happens again, and note down what was on when it
went. If it seems to be at random get a spark in and get him to do an
insulation test at 250v with live and neutral joined to earth with
everything connected. It's not accepted practice but it usually finds
the fault! In my mind nothing has happened that seems especially odd,
and other than doing a quick test of earth loop impedance and RCD trip
times for peace of mind, I wouldn't look any further and advise to
wait and see.

As mentioned in my original post, it was the thought of it happening
during my imminent holiday and leaving the fridge/freezer unpowered
that troubled me most. But as you saw up-thread, I can at least avoid
that risk by powering it from the cooker socket. Nevertheless, that's
hardly satisfactory so I won't be comfortable until I've diagnosed the
problem properly.

I've arranged for the original installing electrician to visit this
evening. Apart from anything else he wants to do, I propose to repeat
my earlier experiment. Both with the various devices connected and
also disconnected.

It's a shame you don't live in Herefordshire or I'd offer to pop round
and do a quick check for a cup of coffee!

Indeed! But a very welcome second-best would be for you to hang on in
here with me in the thread until either I get a resolution or terminal
boredom sets in ;-)

--
Terry, West Sussex, UK

On Tue, 10 Jul 2007 17:24:17 +0100, Terry Pinnell
wrote:

Graham wrote:

On Tue, 10 Jul 2007 09:30:24 +0100, Terry Pinnell
wrote:

Terry Pinnell wrote:

This puzzle now has another twist. I decided to do some methodical
leakage tests. My intention was to introduce a leakage from the live
connection of the circuit under test to a convenient earth, and
observe what tripped. That would at least confirm that I understood
what behaviour I was *supposed* to get from my Crabtree StarBreaker
CU. I used a couple of robust 15k resistors in parallel, theoretically
giving me a leakage around 32 mA (in my UK 240 V circuits).

I decided to start with an unimportant circuit, which also had an
extra RCD unit over and above the main CU. This is a double socket RCD
in the garage, fed from #3 on the Main Switch (non-RCD) side of the
CU. As expected, momentarily connecting this leakage current
immediately tripped the garage RCD. However, to my surprise, maybe 1-2
seconds later (with the leakage removed), the *main* switch on the CU
was tripped. So my PC and various household devices and clocks went
down despite my cunning plan ;-)

I'd not have expected this to happen, so could someone offer a
possible explanation please? Does it offer more insight into the odd
behaviour already reported?

In case it helps, the electrician's scrawled installation notes record
trip times of 18/19 ms for all the RCD circuits, and 7 ms for the
external garage RCD unit. There are various other columns like 'Loop
Impedance', 'CPC-CPC ohms', 'Ph-Ph ohms', 'R1+R2 or R2 ohms'; they
mean nothing to me but please let me know if they could help the
diagnosis.

Pondering this over a coffee shortly after hitting Send, I realised
that I was wrong to imply the devices on this circuit were
insignificant. I left all the devices in place when I applied the
leakage. Amongst other things, I have an ancient large DC power supply
in my shed/workshop (30A), permanently connected to provide automatic
garden lighting at dusk. I'm wondering if perhaps some sort of
inductive effect might be responsible? Could the sudden removal of
power from that and other lower-rated transformers have had the effect
observed? If so, my starting choice was poor, and I'll try another
circuit. Or maybe disconnect the two plugs from the garage RCD unit.


Can you confirm that it was the main switch on the far left that
tripped or was it the RCD in the middle?

Thanks Graham, appreciate your reply. Yes, it was the RCD switch that
had opened.

I suspect that the socket
outlet only disconnects the live conductor and not the neutral, very
common, hence your leakage providing a link between N and E possibly
combined with the power supply tripping the RCD. The main switch on
the left is purely a switch and contains no over current or RCD
device, if that has turned itself off then someone's playing tricks or
it needs to be changed, however I have never come across that 15
years.

On you main board the switch on the far left controls everything up to
the RCD (RCD included), and the RCD everything after that. I my
experience it's usually caused by an appliance somewhere, washing
machine, cooker and anything plugged in outside seem to be the popular
ones. Other less likely causes are loose contacts in a socket, and
mice.

Wait and see if it happens again, and note down what was on when it
went. If it seems to be at random get a spark in and get him to do an
insulation test at 250v with live and neutral joined to earth with
everything connected. It's not accepted practice but it usually finds
the fault! In my mind nothing has happened that seems especially odd,
and other than doing a quick test of earth loop impedance and RCD trip
times for peace of mind, I wouldn't look any further and advise to
wait and see.

As mentioned in my original post, it was the thought of it happening
during my imminent holiday and leaving the fridge/freezer unpowered
that troubled me most. But as you saw up-thread, I can at least avoid
that risk by powering it from the cooker socket. Nevertheless, that's
hardly satisfactory so I won't be comfortable until I've diagnosed the
problem properly.

I've arranged for the original installing electrician to visit this
evening. Apart from anything else he wants to do, I propose to repeat
my earlier experiment. Both with the various devices connected and
also disconnected.

It's a shame you don't live in Herefordshire or I'd offer to pop round
and do a quick check for a cup of coffee!

Indeed! But a very welcome second-best would be for you to hang on in
here with me in the thread until either I get a resolution or terminal
boredom sets in ;-)

If it only happened the once I would be inclined to leave it. There
are a whole heap of things that can cause it trip, most of which are
one time only events that dissappear as soon as it happens, such as
power spikes. I would only investgate it heavily if it was tripping
regually ( once a month) and causing a nusance, otherwise your not
likely to find a fault. As for plugging the freezer into the cooker,
go ahead, it is common (and considered good practice) to provide a
single socket that is not RCD protected and on its own breaker for it,
Although that won't be allowed under the next regs, you will however
be able to plug it in in the bathroom......

Graham

"Terry Pinnell" wrote in message
...
This puzzle now has another twist. I decided to do some methodical
leakage tests. My intention was to introduce a leakage from the live
connection of the circuit under test to a convenient earth, and
observe what tripped. That would at least confirm that I understood
what behaviour I was *supposed* to get from my Crabtree StarBreaker
CU. I used a couple of robust 15k resistors in parallel, theoretically
giving me a leakage around 32 mA (in my UK 240 V circuits).

I decided to start with an unimportant circuit, which also had an
extra RCD unit over and above the main CU. This is a double socket RCD
in the garage, fed from #3 on the Main Switch (non-RCD) side of the
CU. As expected, momentarily connecting this leakage current
immediately tripped the garage RCD. However, to my surprise, maybe 1-2
seconds later (with the leakage removed), the *main* switch on the CU
was tripped. So my PC and various household devices and clocks went
down despite my cunning plan ;-)

I'd not have expected this to happen, so could someone offer a
possible explanation please? Does it offer more insight into the odd
behaviour already reported?

In case it helps, the electrician's scrawled installation notes record
trip times of 18/19 ms for all the RCD circuits, and 7 ms for the
external garage RCD unit. There are various other columns like 'Loop
Impedance', 'CPC-CPC ohms', 'Ph-Ph ohms', 'R1+R2 or R2 ohms'; they
mean nothing to me but please let me know if they could help the
diagnosis.


Well, that's certainly strange to me, and like you, not what I would have
expected. I suspect that you are now getting beyond my level of expertise
with this, so if I catch up with him in the next day or two, I will ask my
next door neighbour, who is a fully UK qualified electrician, and talks
about this sort of stuff all the time.

Arfa
--
Terry, West Sussex, UK