2 year old split load MK CU with 30mA RCD, PME supply, lighting circuits
and outbuilding (with own CU/RCD) on non-protected side, everything else
on protected side, no history of tripping.

Just had the RCD trip out, went down to investigate, it tripped straight
out again, twice, so initially appeared to be a fault remaining
somewhere. To identify which circuit I switched off all MCBs on
protected side, the RCD then reset OK, so switched on MCBs one at a time
expecting RCD to trip when I reached the offending circuit, but they all
came back OK.

Of course now I wish I'd done it the other way round, switching *off*
MCBs one at a time attempting RCD reset after each. Still seems strange
behaviour though, will see if it re-occurs, any possible explanations
for the sequence of events?

Luckily I was at home when it happened, if nothing else this serves as a
reminder that I really ought to have a non-protected circuit using a
spare way on the CU for fridge/freezer (perhaps central heating too) and
to fit a rechargeable battery back in the radio alarm clock.

Andy Burns wrote:

2 year old split load MK CU with 30mA RCD, PME supply, lighting circuits
and outbuilding (with own CU/RCD) on non-protected side, everything else
on protected side, no history of tripping.

Just had the RCD trip out, went down to investigate, it tripped straight
out again, twice, so initially appeared to be a fault remaining
somewhere. To identify which circuit I switched off all MCBs on
protected side, the RCD then reset OK, so switched on MCBs one at a time
expecting RCD to trip when I reached the offending circuit, but they all
came back OK.

Of course now I wish I'd done it the other way round, switching *off*
MCBs one at a time attempting RCD reset after each. Still seems strange
behaviour though, will see if it re-occurs, any possible explanations
for the sequence of events?

Luckily I was at home when it happened, if nothing else this serves as a
reminder that I really ought to have a non-protected circuit using a
spare way on the CU for fridge/freezer (perhaps central heating too) and
to fit a rechargeable battery back in the radio alarm clock.

couple of sections useful:
http://wiki.diyfaq.org.uk/index.php?title=Rewiring_Tips


NT

wrote:

couple of sections useful:
http://wiki.diyfaq.org.uk/index.php?title=Rewiring_Tips

I'm not knocking you for redirection to wiki/faq, I agree there is good
general information being consolidated there, I indicated I already knew
I'd be better served by an extra non-protected circuit, also it doesn't
seem to have mention causes of RCD trips (nuisance or otherwise) I
suppose it could mention damage to wiring, lamps blowing, damp ingress,
EMI suppression filters, etc.

I was really questioning why simply opening and closing all the MCBs had
allowed the RCD to reset when it initially wouldn't, everything else was
scene-setting.

Thanks anyway.

wrote:

http://wiki.diyfaq.org.uk/index.php?title=Rewiring_Tips

What's the policy on editing the wiki? I see that there is no
requirement to create an account to do so, so I suppose that's a clue,
but is it considered good form to confer with FAQ section maintainers,
or just contribute in good faith and let corrections get made as and
when required? So far I've restrained myself to typo-swatting.

Andy Burns wrote:

wrote:

http://wiki.diyfaq.org.uk/index.php?title=Rewiring_Tips


What's the policy on editing the wiki? I see that there is no
requirement to create an account to do so, so I suppose that's a clue,
but is it considered good form to confer with FAQ section maintainers,
or just contribute in good faith and let corrections get made as and
when required? So far I've restrained myself to typo-swatting.

I think at this stage in its life, let rip and see how it goes. I would
prefer edits were not made anonymously, but that is only my personal
preference.

--
Cheers,

John.

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

In article ,
Andy Burns writes:
wrote:

couple of sections useful:
http://wiki.diyfaq.org.uk/index.php?title=Rewiring_Tips

I'm not knocking you for redirection to wiki/faq, I agree there is good
general information being consolidated there, I indicated I already knew
I'd be better served by an extra non-protected circuit, also it doesn't
seem to have mention causes of RCD trips (nuisance or otherwise) I

I don't think there's any generally accepted definition of a
nuisance trip. I can think of several possible definitions
spanning a very wide range of causes.

suppose it could mention damage to wiring, lamps blowing, damp ingress,
EMI suppression filters, etc.

I was really questioning why simply opening and closing all the MCBs had
allowed the RCD to reset when it initially wouldn't, everything else was
scene-setting.

Possibly some part of the earth leakage pathed has been burned out now.
Maybe the leakage is only marginal against the breaker's trip level.

--
Andrew Gabriel

Andy Burns wrote:
wrote:

couple of sections useful:
http://wiki.diyfaq.org.uk/index.php?title=Rewiring_Tips

I'm not knocking you for redirection to wiki/faq, I agree there is good
general information being consolidated there, I indicated I already knew
I'd be better served by an extra non-protected circuit, also it doesn't
seem to have mention causes of RCD trips (nuisance or otherwise) I
suppose it could mention damage to wiring, lamps blowing, damp ingress,
EMI suppression filters, etc.

I was really questioning why simply opening and closing all the MCBs had
allowed the RCD to reset when it initially wouldn't, everything else was
scene-setting.

Thanks anyway.

I was thinking of the discussion of RCBOs. Fitting them really is the
best approach to these situations. Imho anyway. Article explains why
IIRC.


NT

wrote:

I was thinking of the discussion of RCBOs. Fitting them really is the
best approach to these situations.

Yes I re-read it while correcting some typos and realised it was
discussing multiple RCBOs vs one or more RCDs.

In article ,
Andy Burns wrote:
Just had the RCD trip out, went down to investigate, it tripped straight
out again, twice, so initially appeared to be a fault remaining
somewhere. To identify which circuit I switched off all MCBs on
protected side, the RCD then reset OK, so switched on MCBs one at a time
expecting RCD to trip when I reached the offending circuit, but they all
came back OK.

Snag is an MCB only isolates the line and an RCD will trip if a fault is
in the neutral. Of course it gives you a 50/50 chance of finding out which
circuit it is.

--
*Errors have been made. Others will be blamed.

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

Andrew Gabriel wrote:

Possibly some part of the earth leakage pathed has been burned out now.
Maybe the leakage is only marginal against the breaker's trip level.

Or perhaps something that got wet and has now dried out?

Sensitive "earth leakage" clamp meters like this
http://www.martindale-electric.co.uk/clamp.htm#cm67
are now being promoted as a good way of tracing faults causing RCDs to trip.

--
Andy

In an earlier contribution to this discussion,
Andy Wade wrote:

Andrew Gabriel wrote:

Possibly some part of the earth leakage pathed has been burned out
now. Maybe the leakage is only marginal against the breaker's trip
level.

Or perhaps something that got wet and has now dried out?

Sensitive "earth leakage" clamp meters like this
http://www.martindale-electric.co.uk/clamp.htm#cm67
are now being promoted as a good way of tracing faults causing RCDs
to trip.


Fascinating! Can you hire them - 'cos you could replace quite a lot of
potentially faulty kit for the £300 cost of buying one?
--
Cheers,
Roger
______
Email address maintained for newsgroup use only, and not regularly
monitored.. Messages sent to it may not be read for several weeks.
PLEASE REPLY TO NEWSGROUP!

In article ,
Roger Mills wrote:

In an earlier contribution to this discussion,
Andy Wade wrote:
Sensitive "earth leakage" clamp meters like this
http://www.martindale-electric.co.uk/clamp.htm#cm67

Fascinating! Can you hire them - 'cos you could replace quite a
lot of potentially faulty kit for the £300 cost of buying one?

I made a cruder version of that a couple of years
ago, when trying to trace an RCD trip. It had
very little measuring accuracy, just an indication
whether the unbalance current was larger or smaller
than 15mArms.

Started off with one of those RCDs built into a
13A plugtop. Stripped all comps off the internal
pcb except the Current Transformer and the two
mains wires looping through it. Then terminated
the secondary of the CT with a pair of diodes and
a burden resistor (10k to start with afair). Then
brought out a couple of wires for connection to
a digital multimeter, ( on the 200mVrms range).

I wired a 15k resistor across L-E in a 13A plug
and plugged that into the modified RCD as a
15mArms calibration current and noted the reading
on the DMM.

It worked ok. I was surprised at the very low
unbalance current for most items.

BTW: It did not help in locating the RCD trip
because the fault was actually an N-E short that
only produced a tripping unbalance during the
transient startup surge of a heavy load, (say a
vacuum cleaner, or computer, etc).

--
Tony Williams.

Andy Wade wrote:

Or perhaps something that got wet and has now dried out?

I realise that things could have changed during my reset attempts,
either by an appliance that I've not used since remaining on standby, or
the wind changing direction, or self heating/drying from the leak
itself, but the sequence of events was all within just a few seconds,
and it definitely wouldn't initially reset with the MCBs on, but then it
would reset with them off and didn't trip as they were all turned back on.

Sensitive "earth leakage" clamp meters like this
http://www.martindale-electric.co.uk/clamp.htm#cm67
are now being promoted as a good way of tracing faults causing RCDs to
trip.

Useful to know, but excessive to trace a single episode ...

Andy Wade wrote:

Andrew Gabriel wrote:

Possibly some part of the earth leakage pathed has been burned out
now. Maybe the leakage is only marginal against the breaker's trip level.


Or perhaps something that got wet and has now dried out?

Sensitive "earth leakage" clamp meters like this
http://www.martindale-electric.co.uk/clamp.htm#cm67
are now being promoted as a good way of tracing faults causing RCDs to
trip.

Ohh nice... handy they numbered it the same as the Honeywell prog stat
to save having to remember another number. ;-)

I suppose the slightly cruder way I use to enhance the resolution of my
clamp meter could equally well be applied in these circumstances...

For doing accurate(ish) low current measurements with my "ordinary" true
RMS meter, I have a special short extension lead with about a meter of
outer insulation stripped from it in the middle, and each of the
conductors cable tied into ten turn coils. You can then clamp round one
of the coils and read ten times the actual current flow.

One could knock up a jig that allowed a flyling lead to be taken to the
CU, and the original leg of the power circuit taken to a junction box on
the test jig, and it provides a number of pre-wound coils to clamp round.

--
Cheers,

John.

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

Andy Burns wrote:
2 year old split load MK CU with 30mA RCD, PME supply, lighting circuits
and outbuilding (with own CU/RCD) on non-protected side, everything else
on protected side, no history of tripping.

Just had the RCD trip out, went down to investigate, it tripped straight
out again, twice, so initially appeared to be a fault remaining
somewhere. To identify which circuit I switched off all MCBs on
protected side, the RCD then reset OK, so switched on MCBs one at a time
expecting RCD to trip when I reached the offending circuit, but they all
came back OK.

Of course now I wish I'd done it the other way round, switching *off*
MCBs one at a time attempting RCD reset after each. Still seems strange
behaviour though, will see if it re-occurs, any possible explanations
for the sequence of events?

Luckily I was at home when it happened, if nothing else this serves as a
reminder that I really ought to have a non-protected circuit using a
spare way on the CU for fridge/freezer (perhaps central heating too) and
to fit a rechargeable battery back in the radio alarm clock.
..
Sounds similar to the reason that GFI (so called Ground Fault
Interrupter) outlets (or the equivalent equipped circuit breaker) are
not recommended here (Canada) for certain appliance circuits.
They are recommended for wet and 'outside' locations.
Reason given being that GFI operate on unbalance of current in the live
and neutral wires Some appliances (fridges/freezers etc.) may have
unbalances when starting. Nothing worse that going away and coming back
to a freezer full of rotten food!