Tripping Mains circuit - how to isolate?

[Terry Pinnell]

Hope someone can help me with this domestic problem please.
Intermittently the consumer unit (which I had installed a few months
ago to replace the old conventional 'fuse-box') is cutting off the
main supply. Upstairs and downstairs lights etc are left on, but
anything connected to mains sockets loses power. Just the one MCB is
tripping. So something on the 'ring main' is presumably causing this.
The big snag is that it's *intermittent*. First happened a couple of
months ago, then again 2 weeks later. Then nothing until yesterday,
when it happened twice within an hour. On that last occasion at least
no one was actively using anything (my wife and I were in the garden
when we noticed the pond pump had suddenly stopped).

As soon as I flip the trip-switch back, power comes straight back. I
have *dozens* of things connected to these 3-hole mains sockets. From
domestic stuff like washing machine, gas boiler, freezer, dishwasher
etc, to PC printer, scanner, desk-lamp, Pocket PC cradle, etc, etc.
Dozens. So it's a daunting task to isolate the cause, but that's
clearly what I need to do.

Could someone confirm the basics please? Is it a matter of
methodically using my DMM on a high Ohms range between the Live and
Earth pins of every mains plug involved? But, if the fault is
intermittent, presumably that won't work! (Unless that particular unit
just happens to be in its 'leaky' state when I'm taking the reading.)

Coming at it another way, is there some device (maybe to make myself)
which I can successively interpose at each outlet socket so that, when
the next trip occurs it will signal whether *that* unit was
responsible (with say a battery-powered LED)? It might take a while,
but it seems to me that at least that approach would eventually
isolate it.

Needless to say, I'm keen to fix this asap. Apart from re-setting
microwave and cooker clocks etc, the greatest PITA is recovering PC
stuff.

 

[I.F.]

Hope someone can help me with this domestic problem please.
Intermittently the consumer unit (which I had installed a few months
ago to replace the old conventional 'fuse-box') is cutting off the
main supply. Upstairs and downstairs lights etc are left on, but
anything connected to mains sockets loses power. Just the one MCB is
tripping. So something on the 'ring main' is presumably causing this.
The big snag is that it's *intermittent*. First happened a couple of
months ago, then again 2 weeks later. Then nothing until yesterday,
when it happened twice within an hour. On that last occasion at least
no one was actively using anything (my wife and I were in the garden
when we noticed the pond pump had suddenly stopped).

As soon as I flip the trip-switch back, power comes straight back. I
have *dozens* of things connected to these 3-hole mains sockets. From
domestic stuff like washing machine, gas boiler, freezer, dishwasher
etc, to PC printer, scanner, desk-lamp, Pocket PC cradle, etc, etc.
Dozens. So it's a daunting task to isolate the cause, but that's
clearly what I need to do.

Could someone confirm the basics please? Is it a matter of
methodically using my DMM on a high Ohms range between the Live and
Earth pins of every mains plug involved? But, if the fault is
intermittent, presumably that won't work! (Unless that particular unit
just happens to be in its 'leaky' state when I'm taking the reading.)

Coming at it another way, is there some device (maybe to make myself)
which I can successively interpose at each outlet socket so that, when
the next trip occurs it will signal whether *that* unit was
responsible (with say a battery-powered LED)? It might take a while,
but it seems to me that at least that approach would eventually
isolate it.

Needless to say, I'm keen to fix this asap. Apart from re-setting
microwave and cooker clocks etc, the greatest PITA is recovering PC
stuff.

Hire a certificated mains appliance mains leakage tester for a day and test
everything on the wall outlets one by one - I think the equipment is called
a PAT tester, its an acronym for something but I don't know what!

 

[Fred Bloggs]

Hope someone can help me with this domestic problem please.
Intermittently the consumer unit (which I had installed a few months
ago to replace the old conventional 'fuse-box') is cutting off the
main supply. Upstairs and downstairs lights etc are left on, but
anything connected to mains sockets loses power. Just the one MCB is
tripping. So something on the 'ring main' is presumably causing this.
The big snag is that it's *intermittent*. First happened a couple of
months ago, then again 2 weeks later. Then nothing until yesterday,
when it happened twice within an hour. On that last occasion at least
no one was actively using anything (my wife and I were in the garden
when we noticed the pond pump had suddenly stopped).

As soon as I flip the trip-switch back, power comes straight back. I
have *dozens* of things connected to these 3-hole mains sockets. From
domestic stuff like washing machine, gas boiler, freezer, dishwasher
etc, to PC printer, scanner, desk-lamp, Pocket PC cradle, etc, etc.
Dozens. So it's a daunting task to isolate the cause, but that's
clearly what I need to do.

Could someone confirm the basics please? Is it a matter of
methodically using my DMM on a high Ohms range between the Live and
Earth pins of every mains plug involved? But, if the fault is
intermittent, presumably that won't work! (Unless that particular unit
just happens to be in its 'leaky' state when I'm taking the reading.)

Coming at it another way, is there some device (maybe to make myself)
which I can successively interpose at each outlet socket so that, when
the next trip occurs it will signal whether *that* unit was
responsible (with say a battery-powered LED)? It might take a while,
but it seems to me that at least that approach would eventually
isolate it.

Needless to say, I'm keen to fix this asap. Apart from re-setting
microwave and cooker clocks etc, the greatest PITA is recovering PC
stuff.

The only way the MCB could be tripping before the individual circuit CB
is that the MCB is detecting more than overcurrent. If it has arc
detection then there is a real and possibly dangerous condition with the
existing house wiring or the culprit may be an old style wornout bimetal
thermostat switching the mains directly- this would be the boiler and
the refrigeration stuff. Plan on building a multichannel fast
acquisition unit to capture those circuits first- current transformers,
signal conditioned, and smart "pre" triggering is a must- obviously
triggered on MCB trip. You might also contact the engineering department
of the CB maker.

 

[martin griffith]

Hope someone can help me with this domestic problem please.
Intermittently the consumer unit (which I had installed a few months
ago to replace the old conventional 'fuse-box') is cutting off the
main supply. Upstairs and downstairs lights etc are left on, but
anything connected to mains sockets loses power. Just the one MCB is
tripping. So something on the 'ring main' is presumably causing this.
The big snag is that it's *intermittent*. First happened a couple of
months ago, then again 2 weeks later. Then nothing until yesterday,
when it happened twice within an hour. On that last occasion at least
no one was actively using anything (my wife and I were in the garden
when we noticed the pond pump had suddenly stopped).

As soon as I flip the trip-switch back, power comes straight back. I
have *dozens* of things connected to these 3-hole mains sockets. From
domestic stuff like washing machine, gas boiler, freezer, dishwasher
etc, to PC printer, scanner, desk-lamp, Pocket PC cradle, etc, etc.
Dozens. So it's a daunting task to isolate the cause, but that's
clearly what I need to do.

Could someone confirm the basics please? Is it a matter of
methodically using my DMM on a high Ohms range between the Live and
Earth pins of every mains plug involved? But, if the fault is
intermittent, presumably that won't work! (Unless that particular unit
just happens to be in its 'leaky' state when I'm taking the reading.)

Coming at it another way, is there some device (maybe to make myself)
which I can successively interpose at each outlet socket so that, when
the next trip occurs it will signal whether *that* unit was
responsible (with say a battery-powered LED)? It might take a while,
but it seems to me that at least that approach would eventually
isolate it.

Needless to say, I'm keen to fix this asap. Apart from re-setting
microwave and cooker clocks etc, the greatest PITA is recovering PC
stuff.

I'd change the MCB for another, as a first step

Is it an ELCB, or what ever they call it these days, it might be worth
measuring the leakage current, it might just be on the limit. I got an
old elektor scan somewhere with a cct for such a device




martin

 

[Ken Weitzel]

Hope someone can help me with this domestic problem please.
Intermittently the consumer unit (which I had installed a few months
ago to replace the old conventional 'fuse-box') is cutting off the
main supply. Upstairs and downstairs lights etc are left on, but
anything connected to mains sockets loses power. Just the one MCB is
tripping. So something on the 'ring main' is presumably causing this.
The big snag is that it's *intermittent*. First happened a couple of
months ago, then again 2 weeks later. Then nothing until yesterday,
when it happened twice within an hour. On that last occasion at least
no one was actively using anything (my wife and I were in the garden
when we noticed the pond pump had suddenly stopped).

As soon as I flip the trip-switch back, power comes straight back. I
have *dozens* of things connected to these 3-hole mains sockets. From
domestic stuff like washing machine, gas boiler, freezer, dishwasher
etc, to PC printer, scanner, desk-lamp, Pocket PC cradle, etc, etc.
Dozens. So it's a daunting task to isolate the cause, but that's
clearly what I need to do.

Could someone confirm the basics please? Is it a matter of
methodically using my DMM on a high Ohms range between the Live and
Earth pins of every mains plug involved? But, if the fault is
intermittent, presumably that won't work! (Unless that particular unit
just happens to be in its 'leaky' state when I'm taking the reading.)

Coming at it another way, is there some device (maybe to make myself)
which I can successively interpose at each outlet socket so that, when
the next trip occurs it will signal whether *that* unit was
responsible (with say a battery-powered LED)? It might take a while,
but it seems to me that at least that approach would eventually
isolate it.

Needless to say, I'm keen to fix this asap. Apart from re-setting
microwave and cooker clocks etc, the greatest PITA is recovering PC
stuff.

Hi Terry...

Know absolutely nothing about the UK systems out here in the
colonies (Canada); but just a thought for whatever it may be
worth?

IF what you're tripping is ground fault protected, then surely
the first place I'd be looking is at the water/high humidity
devices - you specifically mentioned a pond pump.

FWIW, I have an individual ground fault interruper outlet on the
side of my house - for the car, etc. Even a few drops of snow
or rain on it is likely to cause it to "pop"

Take care.

Ken

 

[Michael A. Terrell]

IF what you're tripping is ground fault protected, then surely
the first place I'd be looking is at the water/high humidity
devices - you specifically mentioned a pond pump.

I've had to replace a small submersible pump in a fish pond because
of leakage current tripping the breaker.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[Don Lancaster]

Hi Terry...

Know absolutely nothing about the UK systems out here in the
colonies (Canada); but just a thought for whatever it may be
worth?

IF what you're tripping is ground fault protected, then surely
the first place I'd be looking is at the water/high humidity
devices - you specifically mentioned a pond pump.

FWIW, I have an individual ground fault interruper outlet on the
side of my house - for the car, etc. Even a few drops of snow
or rain on it is likely to cause it to "pop"

Take care.

Ken

There are several sensitivities of GFI, and those associated with pools
and especially hot tubs can be extreme.

But the general solution is to disconnect half the loads and see if the
problem persists. Then disconnect one quarter of the problem loads.

I had to do this once with a city fire alarm system. Which would trip
only on very windy days. The problem took months to solve.

Finally found a short mid block and twenty feet in the air where the
steel cable on a power drop had sawed its way through the alarm insulation.

--
Many thanks,

Don Lancaster voice phone: (928)428-4073
Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
rss: http://www.tinaja.com/whtnu.xml email: [email protected]

Please visit my GURU's LAIR web site at http://www.tinaja.com

 

[Pooh Bear]

Hope someone can help me with this domestic problem please.
Intermittently the consumer unit (which I had installed a few months
ago to replace the old conventional 'fuse-box') is cutting off the
main supply. Upstairs and downstairs lights etc are left on, but
anything connected to mains sockets loses power. Just the one MCB is
tripping. So something on the 'ring main' is presumably causing this.
The big snag is that it's *intermittent*. First happened a couple of
months ago, then again 2 weeks later. Then nothing until yesterday,
when it happened twice within an hour. On that last occasion at least
no one was actively using anything (my wife and I were in the garden
when we noticed the pond pump had suddenly stopped).

As soon as I flip the trip-switch back, power comes straight back. I
have *dozens* of things connected to these 3-hole mains sockets. From
domestic stuff like washing machine, gas boiler, freezer, dishwasher
etc, to PC printer, scanner, desk-lamp, Pocket PC cradle, etc, etc.
Dozens. So it's a daunting task to isolate the cause, but that's
clearly what I need to do.

Could someone confirm the basics please? Is it a matter of
methodically using my DMM on a high Ohms range between the Live and
Earth pins of every mains plug involved? But, if the fault is
intermittent, presumably that won't work! (Unless that particular unit
just happens to be in its 'leaky' state when I'm taking the reading.)

Coming at it another way, is there some device (maybe to make myself)
which I can successively interpose at each outlet socket so that, when
the next trip occurs it will signal whether *that* unit was
responsible (with say a battery-powered LED)? It might take a while,
but it seems to me that at least that approach would eventually
isolate it.

Needless to say, I'm keen to fix this asap. Apart from re-setting
microwave and cooker clocks etc, the greatest PITA is recovering PC
stuff.

What's the sensitivity of the breaker to earth leakage current ?

If you have lots of smps powered products on your ring you might be
surprised at the accumulated earth current from the Y caps in the EMI
filters. Maybe it's just on the point of tripping all the time ?

Graham

 

[Paul Hovnanian P.E.]

Hope someone can help me with this domestic problem please.
Intermittently the consumer unit (which I had installed a few months
ago to replace the old conventional 'fuse-box') is cutting off the
main supply. Upstairs and downstairs lights etc are left on, but
anything connected to mains sockets loses power. Just the one MCB is
tripping. So something on the 'ring main' is presumably causing this.
The big snag is that it's *intermittent*.

First of all, I have to admit that I'm no expert on UK wiring systems
and codes. With that aside, here's my input:

[snip]

Could someone confirm the basics please? Is it a matter of
methodically using my DMM on a high Ohms range between the Live and
Earth pins of every mains plug involved? But, if the fault is
intermittent, presumably that won't work! (Unless that particular unit
just happens to be in its 'leaky' state when I'm taking the reading.)

Its doubtfull that a DMM will find anything other than a hard fault. If
its intermittent, it could be something nonlinear, i.e. system voltage
causes something to break down that will look OK at low voltage.

Coming at it another way, is there some device (maybe to make myself)
which I can successively interpose at each outlet socket so that, when
the next trip occurs it will signal whether *that* unit was
responsible (with say a battery-powered LED)? It might take a while
but it seems to me that at least that approach would eventually
isolate it.

If I understand ring mains correctly, this is a distribution branck
circuit that has two sources of power. Unlike radial circuits (used here
in the USA), fault current will flow in from both sources and will be
present on each segment of the circuit. The device you build will have
to detect power magnitude and direction.

I don't know if this is safe or complies with code, but you could try to
break the ring and place some overcurrent indication on each source. I'm
not sure how a ring circuit breaker is configured (it would probably
break both sources for an overcurrent on one side), but fuses would make
the problem simpler.

With all that said, don't follow my advice unless you know it meets
local codes!

Needless to say, I'm keen to fix this asap. Apart from re-setting
microwave and cooker clocks etc, the greatest PITA is recovering PC
stuff.

[/QUOTE]

 

[I.F.]

Hope someone can help me with this domestic problem please.
Intermittently the consumer unit (which I had installed a few months
ago to replace the old conventional 'fuse-box') is cutting off the
main supply. Upstairs and downstairs lights etc are left on, but
anything connected to mains sockets loses power. Just the one MCB is
tripping. So something on the 'ring main' is presumably causing this.
The big snag is that it's *intermittent*.

First of all, I have to admit that I'm no expert on UK wiring systems
and codes. With that aside, here's my input:

[snip]

Could someone confirm the basics please? Is it a matter of
methodically using my DMM on a high Ohms range between the Live and
Earth pins of every mains plug involved? But, if the fault is
intermittent, presumably that won't work! (Unless that particular unit
just happens to be in its 'leaky' state when I'm taking the reading.)

Its doubtfull that a DMM will find anything other than a hard fault. If
its intermittent, it could be something nonlinear, i.e. system voltage
causes something to break down that will look OK at low voltage.

Coming at it another way, is there some device (maybe to make myself)
which I can successively interpose at each outlet socket so that, when
the next trip occurs it will signal whether *that* unit was
responsible (with say a battery-powered LED)? It might take a while
but it seems to me that at least that approach would eventually
isolate it.

If I understand ring mains correctly, this is a distribution branck
circuit that has two sources of power. Unlike radial circuits (used here
in the USA), fault current will flow in from both sources and will be
present on each segment of the circuit. The device you build will have
to detect power magnitude and direction.

A ring main has a single source (the fuse for that circuit) its simply both
ends of the ring are connected to the fuse, the ring main can have any
number of radial spurs.

 

[[email protected]]

Sure all the above is probable but heres another.
If you have a spur going to an outside shed or similar then lightening
can suplement the earth current an trip the earth return.
Had to bypass the trip on my water pump circuit for this reason.

 

[Terry Pinnell]

Thanks for all the helpful replies so far. I'm leaning towards the
view that these are what in further reading late last night I've seen
called 'nuisance trips'. IOW maybe something (apart from me) showing
signs of its age. Such as my 15 year old cooker (electric oven, gas
hobs), 14 year old washer, 18 year old gas boiler, etc.

Graham's suggestion about SMPS-powered devices is another possibility.
Presumably the obvious contributors are my PC and Epson Inkjet
printer? (Not sure about other candidates like: flat-bed scanner,
NiCd/NiMh battery charger, SW Radio, Realistic 2006 Radio Scanner,
etc?) But if that was a serious issue wouldn't I have heard a lot more
about it? FWIW, Graham, this Crabtree consumer unit has a prominent
label '8A/30mA', so I assume the sensitivity is 30 mA?

Ken: I have a separate breaker unit on the house socket that takes
power outside to the pond pump. That has never tripped, so I think I
can exclude that as culprit.

The installing electrician (I 'phoned him last night) said one
possibility was something to do with fluorescent lights. He's
mid-European, English is not his first language, so he's rather hard
to understand sometimes. (In the same conversation, when confirming I
could do some leakage tests myself with my DMM, he referred to his own
testing instrument as '250 Watt', when I assume he meant '250 M Ohm'.)
So I may not have grasped that issue about fluorescent lights
properly. But I think I can rule it out anyway based on no one being
in the house on the last occasion.

The 'RCD Protected' circuits are apparently:
- Hot Water Immersion Unit (always switched off at wall)
- Upstairs mains sockets
- Downstairs mains sockets
- 'Office' (treated separately because of all the stuff here)
- Cooker

Fred was the only one who addressed the second part of my post, about
some sort of automatic detection device. Any other thoughts on that
please? On reflection, if the residual current triggering this thing
is the cumulative effect from those 5 circuits above, then I'd need to
interpose the detector in each one somehow, yes? But, given that I'm
obviously not the first consumer with intermittent tripping, there
must be commercial tools around?

The electrician has promised to call in today. I'll report back on
progress. Meanwhile, any further advice would be much appreciated
please.

 

[Arfa Daily]

Hope someone can help me with this domestic problem please.
Intermittently the consumer unit (which I had installed a few months
ago to replace the old conventional 'fuse-box') is cutting off the
main supply. Upstairs and downstairs lights etc are left on, but
anything connected to mains sockets loses power. Just the one MCB is
tripping. So something on the 'ring main' is presumably causing this.
The big snag is that it's *intermittent*.

First of all, I have to admit that I'm no expert on UK wiring systems
and codes. With that aside, here's my input:

[snip]

Could someone confirm the basics please? Is it a matter of
methodically using my DMM on a high Ohms range between the Live and
Earth pins of every mains plug involved? But, if the fault is
intermittent, presumably that won't work! (Unless that particular unit
just happens to be in its 'leaky' state when I'm taking the reading.)

Its doubtfull that a DMM will find anything other than a hard fault. If
its intermittent, it could be something nonlinear, i.e. system voltage
causes something to break down that will look OK at low voltage.

Coming at it another way, is there some device (maybe to make myself)
which I can successively interpose at each outlet socket so that, when
the next trip occurs it will signal whether *that* unit was
responsible (with say a battery-powered LED)? It might take a while
but it seems to me that at least that approach would eventually
isolate it.

If I understand ring mains correctly, this is a distribution branck
circuit that has two sources of power. Unlike radial circuits (used here
in the USA), fault current will flow in from both sources and will be
present on each segment of the circuit. The device you build will have
to detect power magnitude and direction.

A ring main has a single source (the fuse for that circuit) its simply
both ends of the ring are connected to the fuse, the ring main can have
any number of radial spurs.

I don't know if this is safe or complies with code, but you could try to
break the ring and place some overcurrent indication on each source. I'm
not sure how a ring circuit breaker is configured (it would probably
break both sources for an overcurrent on one side), but fuses would make
the problem simpler.

With all that said, don't follow my advice unless you know it meets
local codes!

How about popping down to B & Q or wherever, and picking up one of those
in-line ECLB sockets used for isolating outdoor portable equipment like
lawnmowers ? These often have a higher sensitivity than 'proper' MCBs, so if
you went round the house putting it ahead of each piece of plugged-in
equipment in turn, you might well find that it trips before the MCB on that
circuit, back at the consumer unit.

Just as a matter of interest, we used to have a similar problem at one of my
wife's cafes, that was in premises shared with another business. We finally
tracked it down to that other business's electric kettle. A pinhole of
corrosion in the outer jacket of the element, is a known common problem for
causing this. Electric toasters are another favourite.

Arfa

 

[Ken Taylor]

Thanks for all the helpful replies so far. I'm leaning towards the
view that these are what in further reading late last night I've seen
called 'nuisance trips'. IOW maybe something (apart from me) showing
signs of its age. Such as my 15 year old cooker (electric oven, gas
hobs), 14 year old washer, 18 year old gas boiler, etc.

Graham's suggestion about SMPS-powered devices is another possibility.
Presumably the obvious contributors are my PC and Epson Inkjet
printer? (Not sure about other candidates like: flat-bed scanner,
NiCd/NiMh battery charger, SW Radio, Realistic 2006 Radio Scanner,
etc?) But if that was a serious issue wouldn't I have heard a lot more
about it? FWIW, Graham, this Crabtree consumer unit has a prominent
label '8A/30mA', so I assume the sensitivity is 30 mA?

Ken: I have a separate breaker unit on the house socket that takes
power outside to the pond pump. That has never tripped, so I think I
can exclude that as culprit.

The installing electrician (I 'phoned him last night) said one
possibility was something to do with fluorescent lights. He's
mid-European, English is not his first language, so he's rather hard
to understand sometimes. (In the same conversation, when confirming I
could do some leakage tests myself with my DMM, he referred to his own
testing instrument as '250 Watt', when I assume he meant '250 M Ohm'.)
So I may not have grasped that issue about fluorescent lights
properly. But I think I can rule it out anyway based on no one being
in the house on the last occasion.

The 'RCD Protected' circuits are apparently:
- Hot Water Immersion Unit (always switched off at wall)
- Upstairs mains sockets
- Downstairs mains sockets
- 'Office' (treated separately because of all the stuff here)
- Cooker

Fred was the only one who addressed the second part of my post, about
some sort of automatic detection device. Any other thoughts on that
please? On reflection, if the residual current triggering this thing
is the cumulative effect from those 5 circuits above, then I'd need to
interpose the detector in each one somehow, yes? But, given that I'm
obviously not the first consumer with intermittent tripping, there
must be commercial tools around?

The electrician has promised to call in today. I'll report back on
progress. Meanwhile, any further advice would be much appreciated
please.

While SMPS's can trip an RCD, I'd expect it to do it a lot more often than
every few weeks/months, and at turn-on. The cooker is way more likely to be
the culprit, though you haven't mentioned if any/all of the trips happened
with the washer going (the water being the obvious reason). Another poster's
comment about looking for auxiliary causes (rain, wind, people kicking cats,
whatever) is a good one - see if there's another common cause going on.

You could maybe break the circuit and run from two breakers, but that may
not be possible if the current rating of the cabling then is insufficient.
Possibly start with separating out the office and running it off its own
RCD.

I don't know of any commercial equipment that will help you with this
because of the intermittent nature. Regarding your sparkie's comment about a
250W tester, that may be the maximum power rating of the equipment under
test that his tester can handle. I'd be surprised if it was fluoro lights,
if only because I assume your wiring is similar to Antipodean wiring and the
lighting is on a separate circuit to the power outlets (which are the ones
with the RCD). If the lights are also protected maybe a ballast is breaking
down.....? Oh, and you want to use a Megger to test the insulation, though
at a couple of hundred pounds (RS price) you probably would want a real
reason for buying one.

Cheers.

Ken

 

[Steve]

I've had to replace a small submersible pump in a fish pond because
of leakage current tripping the breaker.

Interesting that others have trouble with pumps. I had an
intermittent RCD trip of the type described, it started off very
infrequent but (fortunately perhaps) it got a lot more frequent so I
could ID the cause by isolating things - turned out to be the central
heating pump, which of course was still pumping fine, so the fault
wasn't exactly obvious.

Steve

 

[Michael A. Terrell]

Interesting that others have trouble with pumps. I had an
intermittent RCD trip of the type described, it started off very
infrequent but (fortunately perhaps) it got a lot more frequent so I
could ID the cause by isolating things - turned out to be the central
heating pump, which of course was still pumping fine, so the fault
wasn't exactly obvious.

Steve

This pump ran 24 hours a day, outdoors in the hot sun. It was filled
with transformer oil for cooling but the heat and vibration broke down
the insulation on the field windings.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[Ken Weitzel]

:

[snip]

A ring main has a single source (the fuse for that circuit) its simply both
ends of the ring are connected to the fuse, the ring main can have any
number of radial spurs.

That modifies the problem slightly. A fault on one of the radials can be
detected by fusing or putting some sort of overcurrent indication on
each. But for a problem on the ring itself, both sides of the loop will
carry part of the overcurrent. So either the ring must be split or
overcurrent detection placed in the middle of the ring must also sense
power direction.

Hi Paul...

For the benefit of the OP, may I add that if he does go the route
of fusing or GFI'ing one of those spurs, that it still won't
necessarily tell him anything.

The one that opens is going to be the one that is either/or more
sensitive to a ground fault, or failing that the one that's faster

Take care.

Ken

 

[Paul Hovnanian P.E.]

[snip]

A ring main has a single source (the fuse for that circuit) its simply both
ends of the ring are connected to the fuse, the ring main can have any
number of radial spurs.

That modifies the problem slightly. A fault on one of the radials can be
detected by fusing or putting some sort of overcurrent indication on
each. But for a problem on the ring itself, both sides of the loop will
carry part of the overcurrent. So either the ring must be split or
overcurrent detection placed in the middle of the ring must also sense
power direction.

 

[Terry Pinnell]

While SMPS's can trip an RCD, I'd expect it to do it a lot more often than
every few weeks/months, and at turn-on. The cooker is way more likely to be
the culprit, though you haven't mentioned if any/all of the trips happened
with the washer going (the water being the obvious reason). Another poster's
comment about looking for auxiliary causes (rain, wind, people kicking cats,
whatever) is a good one - see if there's another common cause going on.

I did suspect the (rather ancient) washing machine when it happened a
few weeks ago. But as I said in my OP, *nothing* was being actively
used on the most recent occasion.

You could maybe break the circuit and run from two breakers, but that may
not be possible if the current rating of the cabling then is insufficient.
Possibly start with separating out the office and running it off its own
RCD.

I don't know of any commercial equipment that will help you with this
because of the intermittent nature. Regarding your sparkie's comment about a
250W tester, that may be the maximum power rating of the equipment under
test that his tester can handle.

During his visit yesterday I realised he had been saying 'Volts', not
'Watts'. ("Votz".) His tester has settings for 250V and 500V. Which of
course is why it's much more suitable than my DMM; although that
sports a handy 200 MOhm range, its 9V presumably provides an
inadequate test of real conditions.

I'd be surprised if it was fluoro lights,
if only because I assume your wiring is similar to Antipodean wiring and the
lighting is on a separate circuit to the power outlets (which are the ones
with the RCD). If the lights are also protected maybe a ballast is breaking
down.....? Oh, and you want to use a Megger to test the insulation, though
at a couple of hundred pounds (RS price) you probably would want a real
reason for buying one.

Turns out that was a tripping cause he'd experienced a couple of
times, but only when light was actually being switched on/off.
Inapplicable here.

Cheers.

Anyway, happy to report that cause now found. The overall 'rating'
when he first applied the tester to the entire house was borderline,
which of course was consistent with such an intermittent fault.
Eventually we isolated that 'iffy' circuit to external garden wiring
which I'd installed a decade ago. Switching to the Ohm meter, we got
erratic readings, typically about 20 M. Interestingly, I'd tentatively
excluded that garden circuit. It was one of a couple (my shed/workshop
being another) that was supplied via another 30 mA RCD unit. But of
course, as both Ken Weitzel and my electrician pointed out, the
consumer unit breaker that did trip was probably already sensing a
small leakage from everything *else* in the house. And/or it may be
faster acting.

After his departure I started tracking down the actual fault. I aim to
complete that today, but I'm pretty sure it will prove to be damp
getting into one or more of my connections. (There are a couple of
external mains sockets, linked by cable running from house. One of
them takes 240V to a relay box at bottom of garden, which switches
lights on at night.) Despite generous use of 'gaffer tape' (which will
be a pain to remove), I expect rain has somehow found a way in!

Thanks to all here for the help and advice, which was much
appreciated.

 

[Ken Taylor]

I did suspect the (rather ancient) washing machine when it happened a
few weeks ago. But as I said in my OP, *nothing* was being actively
used on the most recent occasion.


During his visit yesterday I realised he had been saying 'Volts', not
'Watts'. ("Votz".) His tester has settings for 250V and 500V. Which of
course is why it's much more suitable than my DMM; although that
sports a handy 200 MOhm range, its 9V presumably provides an
inadequate test of real conditions.


Turns out that was a tripping cause he'd experienced a couple of
times, but only when light was actually being switched on/off.
Inapplicable here.


Anyway, happy to report that cause now found. The overall 'rating'
when he first applied the tester to the entire house was borderline,
which of course was consistent with such an intermittent fault.
Eventually we isolated that 'iffy' circuit to external garden wiring
which I'd installed a decade ago. Switching to the Ohm meter, we got
erratic readings, typically about 20 M. Interestingly, I'd tentatively
excluded that garden circuit. It was one of a couple (my shed/workshop
being another) that was supplied via another 30 mA RCD unit. But of
course, as both Ken Weitzel and my electrician pointed out, the
consumer unit breaker that did trip was probably already sensing a
small leakage from everything *else* in the house. And/or it may be
faster acting.

After his departure I started tracking down the actual fault. I aim to
complete that today, but I'm pretty sure it will prove to be damp
getting into one or more of my connections. (There are a couple of
external mains sockets, linked by cable running from house. One of
them takes 240V to a relay box at bottom of garden, which switches
lights on at night.) Despite generous use of 'gaffer tape' (which will
be a pain to remove), I expect rain has somehow found a way in!

Thanks to all here for the help and advice, which was much
appreciated.

Glad you have (or soon will!) find the problem. Rather than gaffer tape, get
hold of some heatshrink tubing, the type with the 'glue' in it - much better
weatherproofing.

Cheers.

Ken