I'm having a bit of "fun" with my electrical system at home, and would
appreciate any advice.

The system has a RCD between the meter and the consumer unit (not sure
why, it was there when I moved in, but it has proved useful). The earth
is a spike in the ground at the back of the house.

Thursday night just as I turned the shower on, the RCD tripped out. So
I found a torch and reset the trip in the dark. I tried the shower
again, and off went the power again. I concluded that the shower had
died (it is 10-12 years old, so that seemed a fair conclusion).

This evening (Saturday), I was busy cooking my evening meal (on an
electric hob), and after about 10 minutes, off goes the power. Having
been moving the wiring for the boiler earlier in the day, I wondered if
I had got something wrong on that, so I turned off the RCD for that on
the consumer unit, put the power back on, and went back to cooking. 5
minutes or so later (certainly not straight away), off goes the power
again. I turned off the hob (which is 15 months old, so should have
some life in it yet), reset the trip, then tried the other two rings,
and within a minute or so, off goes the power again. The good news is
that by now the spuds are done, so at least I can get something to eat.

Having eaten the spuds, and thought about it, I consulted my tame
electrician (Dad). One thought that crossed my mind was that after a
long dry summer, the earth spike could be making a bad contact (*), so
whilst it was a long shot, it was worth a try. So I slowly poured some
salty water round the spike, allowing it to soak in. I then tried the
hob again for 20 minutes or so, and this time it was fine.

(*) memories of tales of old phone systems not working until a bucket of
water was tipped over the earth lead.

So, is it a coincidence that watering the earth spike has got things
working ?. Is there anything else I should do (getting it looked at
professionally will be arranged next week) ?.


TIA

Adrian
--
To Reply :
replace "news" with "adrian" and "nospam" with "ffoil"
Sorry for the rigmarole, If I want spam, I'll go to the shops
Every time someone says "I don't believe in trolls", another one dies.

In article , Adrian Simpson
writes
I'm having a bit of "fun" with my electrical system at home, and would
appreciate any advice.

The system has a RCD between the meter and the consumer unit (not sure
why, it was there when I moved in, but it has proved useful). The earth
is a spike in the ground at the back of the house.

Thursday night just as I turned the shower on, the RCD tripped out. So
I found a torch and reset the trip in the dark. I tried the shower
again, and off went the power again. I concluded that the shower had
died (it is 10-12 years old, so that seemed a fair conclusion).

This evening (Saturday), I was busy cooking my evening meal (on an
electric hob), and after about 10 minutes, off goes the power. Having
been moving the wiring for the boiler earlier in the day, I wondered if
I had got something wrong on that, so I turned off the RCD for that on
the consumer unit, put the power back on, and went back to cooking. 5
minutes or so later (certainly not straight away), off goes the power
again. I turned off the hob (which is 15 months old, so should have
some life in it yet), reset the trip, then tried the other two rings,
and within a minute or so, off goes the power again. The good news is
that by now the spuds are done, so at least I can get something to eat.

Having eaten the spuds, and thought about it, I consulted my tame
electrician (Dad). One thought that crossed my mind was that after a
long dry summer, the earth spike could be making a bad contact (*), so
whilst it was a long shot, it was worth a try. So I slowly poured some
salty water round the spike, allowing it to soak in. I then tried the
hob again for 20 minutes or so, and this time it was fine.

(*) memories of tales of old phone systems not working until a bucket of
water was tipped over the earth lead.

So, is it a coincidence that watering the earth spike has got things
working ?. Is there anything else I should do (getting it looked at
professionally will be arranged next week) ?.


TIA

Adrian

The RCD has nothing to do with the earth as such. All it does is look at
the current into the protected circuits, on the live and checks that the
same comes back out on the neutral. Any imbalance i.e. leakage to earth
then it will trip the level needs to be about 15 ma or so..

Usual causes are leakage between heating elements to earth especially
cookers, immersion heaters, and anything which uses an enclosed heating
elements inside a metal case.

Another cause sometimes is if the earth and neutral are inadvertently
connected together anywhere. This will result in nuisance tripping when
the load on the system increases. Some of the current will be carried by
the earth rod and if you have made this a *better* earth then a part of
the fault current will now be diverted via this route back to the
substation and hence the imbalance between power in on the live and out
on the neutral will cause the trip to drop....
--
Tony Sayer

In uk.d-i-y, tony sayer wrote:

The RCD has nothing to do with the earth as such. All it does is look at
the current into the protected circuits, on the live and checks that the
same comes back out on the neutral. Any imbalance i.e. leakage to earth
then it will trip the level needs to be about 15 ma or so..

This is an accurate description of a modern RCCD. However, the earlier
type was voltage-operated - it would look to see when the house earth
potential had risen to more than 50V above that from the earth rod (!).
This type of voltage-operated earth breaker hasn't been fitted for 15+
years. (You can usually tell the difference by reading the case: the
more recent current-balance ones will include an indication of the current
sensitivity, usual values being 30mA or 100mA. The older voltage-operated
ones tend not to have anything too detailed written on them, and will
have their own relatively thin (4mmsq, say) earth wire going off to an
earth rod).

But it's quite possible that the original poster has just such a unit.
(It's also possible that it's a whole-house current-balance one). Whichever
the exact type of the RCD, there *is* likely to be some sort of a fault.
The whole-house RCD will have been fitted precisely because the supply
can't provide a good earth - common in rural feeds, but also on some
estates (our first house in Abingdon had such an arrangement). The
dicking-about with the central heating wiring might have resulted in a
small increase in earth leakage, such that the whole-house breaker now
has less margin for other small leaks (e.g. from the cooker).

It's not a bad idea to get an intelligent and experienced electrician in
at this point, who will have suitable test gear and the practice in
using it. At our previous place I found just such a gem, who as part of
the 50-quid inspection did some excellent fault finding on the earth
leakage side of things (we had both a rather-too-sensitive nominal-30mA
trip which went out at about 13-14 mA: the 30mA is a nominal value and
is specced to mean "will pop at no more than 30, won't pop below 15". And
we had both a grill and a cooker element which leaked a bit too much; this,
added to the immodest number of computeren with their mains input filters
each leaking 1-3 mAs, accounted for the excessive number of nuisance trips).
So, in this case at least, it was well worth getting a Professional in!

HTH, Stefek

"Adrian Simpson" wrote in message
...
I'm having a bit of "fun" with my electrical system at home, and would
appreciate any advice.

The system has a RCD between the meter and the consumer unit (not sure
why, it was there when I moved in, but it has proved useful). The earth
is a spike in the ground at the back of the house.

Thursday night just as I turned the shower on, the RCD tripped out. So
I found a torch and reset the trip in the dark. I tried the shower
again, and off went the power again. I concluded that the shower had
died (it is 10-12 years old, so that seemed a fair conclusion).

This evening (Saturday), I was busy cooking my evening meal (on an
electric hob), and after about 10 minutes, off goes the power. Having
been moving the wiring for the boiler earlier in the day, I wondered if
I had got something wrong on that, so I turned off the RCD for that on
the consumer unit, put the power back on, and went back to cooking. 5
minutes or so later (certainly not straight away), off goes the power
again. I turned off the hob (which is 15 months old, so should have
some life in it yet), reset the trip, then tried the other two rings,
and within a minute or so, off goes the power again. The good news is
that by now the spuds are done, so at least I can get something to eat.

Having eaten the spuds, and thought about it, I consulted my tame
electrician (Dad). One thought that crossed my mind was that after a
long dry summer, the earth spike could be making a bad contact (*), so
whilst it was a long shot, it was worth a try. So I slowly poured some
salty water round the spike, allowing it to soak in. I then tried the
hob again for 20 minutes or so, and this time it was fine.

(*) memories of tales of old phone systems not working until a bucket of
water was tipped over the earth lead.

So, is it a coincidence that watering the earth spike has got things
working ?. Is there anything else I should do (getting it looked at
professionally will be arranged next week) ?.


TIA

Adrian


You could try putting another metre length on the earth spike to take it
further in to the ground. :-))

One thing I've noticed on new installation I'm visiting, is that the RCD's
which are fitted in the mains supply like yours, are only rated at 30mA
imbalance fault signal. This is really not adequate for a whole house
supply. This, to me, is erring on the "to safe to be properly functional"
side of things and is now causing a lot of nuisance breaks in whole house
supplies that are being installed these days.

A split load consumer unit seems to be a better design for a whole house
supply system and this is the road I'd advise you to take, if not already
installed, in your property. The split load CU separates low Wattage loads
like lighting and ventilation fans etc. from heavier loads like heating
circuits and larger domestic appliances fitted to other ring circuits
throughout the house. The heavier loads are controlled by an RCD with
individual MCB's to each circuit and depending on the load you may be
putting on the supply, can be rated up to 100mA fault signal before a trip
is activated. The lighter loads are controlled through a standard double
pole mains switch. This is safer because it leaves the lighting on so
you're not stumbling around in the dark to find torches and things, and if
the it is the lighting that has tripped off, then you can still plug in a
table to see your way around.

I still think designers of these electrical installations are not
considering that many people are actually drawing a lot more power from the
supply than they think and they are not allowing for heavier heating
elements in showers and washing and cooking appliances, and the fact that a
lot more dwellings can have more than one of each of these items installed
today.

The only place I now err on the side of "better safe than sorry" is in the
earthing continuity I install. If I can't get below 2 ohm impedance to
earth on any of my installations, then I feel that I have failed to provide
an adequate safety measure, even though an allowance of 10 ohms or below is
required to pass current testing approval.

These are just my thoughts on things. So. End of ramble. :-)

On 20 Sep 2003 20:08:52 GMT, wrote:

In uk.d-i-y, tony sayer wrote:

The RCD has nothing to do with the earth as such. All it does is look at
the current into the protected circuits, on the live and checks that the
same comes back out on the neutral. Any imbalance i.e. leakage to earth
then it will trip the level needs to be about 15 ma or so..

This is an accurate description of a modern RCCD. However, the earlier
type was voltage-operated - it would look to see when the house earth
potential had risen to more than 50V above that from the earth rod (!).

Must admit, this was the first thing that crossed my mind when I read
this thread. First thing, get someone who knows the difference to see if
you have a voltage operated trip.

On Sat, 20 Sep 2003 20:08:00 +0100, Adrian Simpson
wrote:

So, is it a coincidence that watering the earth spike has got things
working ?

No, chances are that it's a voltage-activated RCD. Is it old ? 15-20
years ? These things were a bit prone to this problem.

--
Blind drunk - Please ignore all postings I make,
until I sober up enough to notice the .sig file
that has been attached to them.
Thank you.

wrote in message
...
In uk.d-i-y, tony sayer wrote:

The RCD has nothing to do with the earth as such. All it does is look at
the current into the protected circuits, on the live and checks that the
same comes back out on the neutral. Any imbalance i.e. leakage to earth
then it will trip the level needs to be about 15 ma or so..

This is an accurate description of a modern RCCD. However, the earlier
type was voltage-operated - it would look to see when the house earth
potential had risen to more than 50V above that from the earth rod (!).
This type of voltage-operated earth breaker hasn't been fitted for 15+
years. (You can usually tell the difference by reading the case: the
more recent current-balance ones will include an indication of the current
sensitivity, usual values being 30mA or 100mA. The older voltage-operated
ones tend not to have anything too detailed written on them, and will
have their own relatively thin (4mmsq, say) earth wire going off to an
earth rod).

It could be labelled ELCB if it is one of the older types. Also as you say,
the old units frequently are connected to earth whereas an RCD is not.

Adam

In article ,
"ARWadsworth" writes:

It could be labelled ELCB if it is one of the older types. Also as you say,
the old units frequently are connected to earth whereas an RCD is not.

Some RCD's have earth connections too. A unique feature of a Voltage
Operated ELCB is that it has two separate earth connections -- one
to the house wiring, and the other to the earth rod. It operates by
measuring the voltage between these two connections.

--
Andrew Gabriel

"Andrew Gabriel" wrote in message
...
In article ,
"ARWadsworth" writes:

It could be labelled ELCB if it is one of the older types. Also as you
say,
the old units frequently are connected to earth whereas an RCD is not.

Some RCD's have earth connections too. A unique feature of a Voltage
Operated ELCB is that it has two separate earth connections -- one
to the house wiring, and the other to the earth rod. It operates by
measuring the voltage between these two connections.

--
Andrew Gabriel

I was thinking of it being an RCD (ELCB) with an active earth connection, or
so I would have thought due to the age of the installation as the OP
mentions.

"tony sayer" wrote in message
...
In article , Adrian Simpson
writes
I'm having a bit of "fun" with my electrical system at home, and would
snipped

The RCD has nothing to do with the earth as such. All it does is look at
the current into the protected circuits, on the live and checks that the
same comes back out on the neutral. Any imbalance i.e. leakage to earth
then it will trip the level needs to be about 15 ma or so..

snipped
--
Tony Sayer


http://www.westernautomation.com/pages/demystify.htm

BigWallop wrote:

"Adrian Simpson" wrote in message
...

I'm having a bit of "fun" with my electrical system at home, and would
appreciate any advice.

The system has a RCD between the meter and the consumer unit (not sure
why, it was there when I moved in, but it has proved useful). The earth
is a spike in the ground at the back of the house.

Thursday night just as I turned the shower on, the RCD tripped out. So
I found a torch and reset the trip in the dark. I tried the shower
again, and off went the power again. I concluded that the shower had
died (it is 10-12 years old, so that seemed a fair conclusion).

This evening (Saturday), I was busy cooking my evening meal (on an
electric hob), and after about 10 minutes, off goes the power. Having
been moving the wiring for the boiler earlier in the day, I wondered if
I had got something wrong on that, so I turned off the RCD for that on
the consumer unit, put the power back on, and went back to cooking. 5
minutes or so later (certainly not straight away), off goes the power
again. I turned off the hob (which is 15 months old, so should have
some life in it yet), reset the trip, then tried the other two rings,
and within a minute or so, off goes the power again. The good news is
that by now the spuds are done, so at least I can get something to eat.

Having eaten the spuds, and thought about it, I consulted my tame
electrician (Dad). One thought that crossed my mind was that after a
long dry summer, the earth spike could be making a bad contact (*), so
whilst it was a long shot, it was worth a try. So I slowly poured some
salty water round the spike, allowing it to soak in. I then tried the
hob again for 20 minutes or so, and this time it was fine.

(*) memories of tales of old phone systems not working until a bucket of
water was tipped over the earth lead.

So, is it a coincidence that watering the earth spike has got things
working ?. Is there anything else I should do (getting it looked at
professionally will be arranged next week) ?.


TIA

Adrian



You could try putting another metre length on the earth spike to take it
further in to the ground. :-))

One thing I've noticed on new installation I'm visiting, is that the RCD's
which are fitted in the mains supply like yours, are only rated at 30mA
imbalance fault signal. This is really not adequate for a whole house
supply. This, to me, is erring on the "to safe to be properly functional"
side of things and is now causing a lot of nuisance breaks in whole house
supplies that are being installed these days.



Hear Hear!

I replaced my 30mA with a 100mA and haven't had a nuisance trip since.

By all ,means protect sockets or outsode rings witha sperate 30mA, but
teh amount of leakage off electronic equipment is enough to regurarly
trip 30mA IME.


A split load consumer unit seems to be a better design for a whole house
supply system and this is the road I'd advise you to take, if not already
installed, in your property. The split load CU separates low Wattage loads
like lighting and ventilation fans etc. from heavier loads like heating
circuits and larger domestic appliances fitted to other ring circuits
throughout the house. The heavier loads are controlled by an RCD with
individual MCB's to each circuit and depending on the load you may be
putting on the supply, can be rated up to 100mA fault signal before a trip
is activated. The lighter loads are controlled through a standard double
pole mains switch. This is safer because it leaves the lighting on so
you're not stumbling around in the dark to find torches and things, and if
the it is the lighting that has tripped off, then you can still plug in a
table to see your way around.

I still think designers of these electrical installations are not
considering that many people are actually drawing a lot more power from the
supply than they think and they are not allowing for heavier heating
elements in showers and washing and cooking appliances, and the fact that a
lot more dwellings can have more than one of each of these items installed
today.

The only place I now err on the side of "better safe than sorry" is in the
earthing continuity I install. If I can't get below 2 ohm impedance to
earth on any of my installations, then I feel that I have failed to provide
an adequate safety measure, even though an allowance of 10 ohms or below is
required to pass current testing approval.

These are just my thoughts on things. So. End of ramble. :-)

One thing I've noticed on new installation I'm visiting, is that the RCD's
which are fitted in the mains supply like yours, are only rated at 30mA
imbalance fault signal. This is really not adequate for a whole house
supply. This, to me, is erring on the "to safe to be properly functional"
side of things and is now causing a lot of nuisance breaks in whole house
supplies that are being installed these days.

Well FWIW our house and the rented ones we own all have 30 ma RCD's and
none have any nuisance tripping problems except when a fault occurred on
an immersion heater when it warmed up a bit.

The only common problems I've seen over the last few years are where a
lot of computers and electronic equipment's are connected to the same
protected circuits. IIRC there are new reg's to cater for this sort of
thing in offices etc now...
--
Tony Sayer

tony sayer wrote:

One thing I've noticed on new installation I'm visiting, is that the RCD's
which are fitted in the mains supply like yours, are only rated at 30mA
imbalance fault signal. This is really not adequate for a whole house
supply. This, to me, is erring on the "to safe to be properly functional"
side of things and is now causing a lot of nuisance breaks in whole house
supplies that are being installed these days.


Well FWIW our house and the rented ones we own all have 30 ma RCD's and
none have any nuisance tripping problems except when a fault occurred on
an immersion heater when it warmed up a bit.

The only common problems I've seen over the last few years are where a
lot of computers and electronic equipment's are connected to the same
protected circuits. IIRC there are new reg's to cater for this sort of
thing in offices etc now...


Yerrs Tony. But I have - lets see.

Two computers.
Two printers
Scanner
Two monitors
PC loudspakers.
PABX
Cisco router
Labgear distribution amplifier.
6 TV's
3 radios

....all of whach are permanently pluugedd in, and, because the remotes
work, probablly have RF filters across the incoming mains.

Plus a random selection of battery chargers and so on. Not to mention an
immersion heater and two electric cookers, two fridges and a deep
freeze, all also permamently on.

Plus 9 extrenal lights and a klargester down the garden, and 2 external
power sockets, that get a leetle moist occasionally...


30mA was nusiance tripping on load for a long time - no pattern to it -
just general earth neutral leakage it would seem. 100mA is rock solid.

I think 30mA is fine for a small house, but not a large one really.

In article , writes
In uk.d-i-y, tony sayer wrote:

The RCD has nothing to do with the earth as such. All it does is look at
the current into the protected circuits, on the live and checks that the
same comes back out on the neutral. Any imbalance i.e. leakage to earth
then it will trip the level needs to be about 15 ma or so..

This is an accurate description of a modern RCCD. However, the earlier
type was voltage-operated - it would look to see when the house earth
potential had risen to more than 50V above that from the earth rod (!).
This type of voltage-operated earth breaker hasn't been fitted for 15+
years. (You can usually tell the difference by reading the case: the
more recent current-balance ones will include an indication of the current
sensitivity, usual values being 30mA or 100mA. The older voltage-operated
ones tend not to have anything too detailed written on them, and will
have their own relatively thin (4mmsq, say) earth wire going off to an
earth rod).

But it's quite possible that the original poster has just such a unit.
(It's also possible that it's a whole-house current-balance one). Whichever
the exact type of the RCD, there *is* likely to be some sort of a fault.
The whole-house RCD will have been fitted precisely because the supply
can't provide a good earth - common in rural feeds, but also on some
estates (our first house in Abingdon had such an arrangement). The
dicking-about with the central heating wiring might have resulted in a
small increase in earth leakage, such that the whole-house breaker now
has less margin for other small leaks (e.g. from the cooker).

It's not a bad idea to get an intelligent and experienced electrician in
at this point, who will have suitable test gear and the practice in
using it. At our previous place I found just such a gem, who as part of
the 50-quid inspection did some excellent fault finding on the earth
leakage side of things (we had both a rather-too-sensitive nominal-30mA
trip which went out at about 13-14 mA: the 30mA is a nominal value and
is specced to mean "will pop at no more than 30, won't pop below 15". And
we had both a grill and a cooker element which leaked a bit too much; this,
added to the immodest number of computeren with their mains input filters
each leaking 1-3 mAs, accounted for the excessive number of nuisance trips).
So, in this case at least, it was well worth getting a Professional in!

HTH, Stefek


Today, the power stayed on, so I got a proper meal tonight :-)

To follow up on the various comments made so far (and many thanks for
them) :

The main RCD was fitted new last December (the previous one had a broken
casing, so it was changed on safety grounds) 30mA trip, 80A capacity.
It is situated on the tails between the meter and the consumer unit, so
only has Live/Neutral connections to it. As the house is a low
occupancy two bed bungalow, then the total consumption is not that high
(one 4 ring ceramic hob, a double oven and 8.5Kw shower being the major
items), everything else could be run off a 13A socket. Not sure why the
earthing is done the way it is, I'm not rural, but I am on the edge of
town. So far as I can tell, none of my neighbours has earthing
arrangement that I have, but I doubt that any of them could tell me what
they do have. The good news is that at least I do have an earth now (it
was not connected up when I moved in).

This morning, I rechecked the wiring that has been disturbed recently,
and all appears to be in order. The change in the central heating
wiring was to moved the switched fused spur unit along the wall a few
inches to make for a better location, the cabling involved is the same
as before (which has been in for 6 weeks or so).


Adrian
--
To Reply :
replace "news" with "adrian" and "nospam" with "ffoil"
Sorry for the rigmarole, If I want spam, I'll go to the shops
Every time someone says "I don't believe in trolls", another one dies.

In uk.d-i-y, Adrian Simpson wrote:

Today, the power stayed on, so I got a proper meal tonight :-)

Good - can't have you Blaining out on us through lack of food ;-)

The main RCD was fitted new last December (the previous one had a broken
casing, so it was changed on safety grounds) 30mA trip, 80A capacity.
It is situated on the tails between the meter and the consumer unit, so
only has Live/Neutral connections to it. As the house is a low
occupancy two bed bungalow, then the total consumption is not that high
.................................................. .... Not sure why the
earthing is done the way it is, I'm not rural, but I am on the edge of
town. So far as I can tell, none of my neighbours has earthing
arrangement that I have, but I doubt that any of them could tell me what
they do have. The good news is that at least I do have an earth now (it
was not connected up when I moved in).

OK, this gives us more information to work with. Your whole-house RCD
is definitely a Modern current-operated one, then. It's no longer thought
Good Practice to fit a single 30mA RCD as a whole-house fitment, actually:
split-load arrangements which leave the lights on and put the more-likely-
to-have-benign-leakage circuits (immersions and cookers) on the non-RCD
side, and the more-likely-to-fault-with-danger-to-human-life circuits
- especially sockets rings "likely" to be used to supply tools used
outside the house - on the RCD side. So whoever fitted the 80A/30mA trip
(you? a sparks?) was following last decade's accepted practice ;-)

IF you're confident in your own competence, you could go split-load at
minimal kit cost by running the tails which now go to the RCD into a
Henley block (fat-arse junction box ;-) from which you'd run tails into
the existing RCD-and-on-to-current-CU, and also out to a new small CU
with say 6 or 8 non-RCD-protected ways, for your lights, cooker, and
immersion/CH circuits. This is *only* safe if you have a decent earth
for these non-RCD circuits, mind! If you're not sure of that, you really
should get a real sparks in. S/he might end up recommending you fit a
time-delayed 100mA-trip RCD to give short enough disconnection times
if your existing earth isn't low resistance enough; downstream of that
you could (and should) still run a split-load arrangement, whether in
a single new CU or the Henley-block-and-two-CUs stylie outlined above.
The difference in both trip ratings and time-to-disconnect between the
100mA time-delayed trip and the 30mA faster-acting trip preserves good
"discrimination", i.e. an earth leakage fault on the 30mA side should
make that trip, and that trip only, disconnect, leaving power on to
your lights and other circuits.

Hope that helps (and thanks for bottom-posting; now move further up
the style scale by trimming the post you're replying to more aggressively
- OK? :-) - Stefek

On Mon, 22 Sep 2003 10:28:58 +0100, tony sayer
wrote:

I'm bugg**ed if I'd rely on a 100 ma trip for protection against accidental contact!...

You won't be, it just feels like it.

--
Smert' spamionam

On Mon, 22 Sep 2003 10:28:58 +0100, tony sayer wrote:

I think 30mA is fine for a small house, but not a large one really.

A whole house RCD should be a 100mA time delayed device. It is there
for circuit protection because the earth loop impedance is (or maybe)
to high for prospective fault currents to be large enough to trip
overload devices within the specified time(s). It is not there for
shock protection.

Well we're running more electronic stuff than that nat P but I'm
bugg**ed if I'd rely on a 100 ma trip for protection against
accidental contact!...

Quite. For that you need a 30mA non-delayed device, even then a belt
through one of those hurts. The delayed/non-delayed action is to
provide discrimination between the devices, the current rating alone
does not guarantee that.

--
Cheers
Dave. pam is missing e-mail

tony sayer wrote:

In article , The Natural Philosopher
writes

tony sayer wrote:


One thing I've noticed on new installation I'm visiting, is that the RCD's
which are fitted in the mains supply like yours, are only rated at 30mA
imbalance fault signal. This is really not adequate for a whole house
supply. This, to me, is erring on the "to safe to be properly functional"
side of things and is now causing a lot of nuisance breaks in whole house
supplies that are being installed these days.


Well FWIW our house and the rented ones we own all have 30 ma RCD's and
none have any nuisance tripping problems except when a fault occurred on
an immersion heater when it warmed up a bit.

The only common problems I've seen over the last few years are where a
lot of computers and electronic equipment's are connected to the same
protected circuits. IIRC there are new reg's to cater for this sort of
thing in offices etc now...


Yerrs Tony. But I have - lets see.

Two computers.
Two printers
Scanner
Two monitors
PC loudspakers.
PABX
Cisco router
Labgear distribution amplifier.
6 TV's
3 radios

...all of whach are permanently pluugedd in, and, because the remotes
work, probablly have RF filters across the incoming mains.

Plus a random selection of battery chargers and so on. Not to mention an
immersion heater and two electric cookers, two fridges and a deep
freeze, all also permamently on.

Plus 9 extrenal lights and a klargester down the garden, and 2 external
power sockets, that get a leetle moist occasionally...


30mA was nusiance tripping on load for a long time - no pattern to it -
just general earth neutral leakage it would seem. 100mA is rock solid.

I think 30mA is fine for a small house, but not a large one really.








Well we're running more electronic stuff than that nat P but I'm
bugg**ed if I'd rely on a 100 ma trip for protection against accidental
contact!...


I don't. I rely on common sense. ;-)

Well we're running more electronic stuff than that nat P but I'm
bugg**ed if I'd rely on a 100 ma trip for protection against accidental
contact!...


I don't. I rely on common sense. ;-)


No argument there then:-))...
--
Tony Sayer

In article , writes


snipped much useful/interesting stuff about current (no pun intended)
domestic wiring practice

I'm trying to get hold of a sparks this week to have a look at it (I
won't touch that end of the circuitry). Who knows when s/he will get
around to looking at it (if my experience of local builders/plumbers is
anything to go by, it could be weeks).

I'm happy working on the load side of the consumer unit, but I don't
touch the CU or the supply side.

Hope that helps (and thanks for bottom-posting; now move further up
the style scale by trimming the post you're replying to more aggressively
- OK? :-) - Stefek

I _never_ top post !. Snipping is always a difficult one, how much
context to leave, how much to remove.

Thanks again.


Adrian
--
To Reply :
replace "news" with "adrian" and "nospam" with "ffoil"
Sorry for the rigmarole, If I want spam, I'll go to the shops
Every time someone says "I don't believe in trolls", another one dies.

Adrian Simpson writes
The main RCD was fitted new last December (the previous one had a broken
casing, so it was changed on safety grounds) 30mA trip, 80A capacity.

It is possible to have an appliance [or eg a shower] which works fine
but has a leak of a few ohms between neutral and earth.
This may not normally trip the RCD.
However, when a nearby kettle and the dishwasher are switched on and
draw 20Amps or so, the neutral-to-earth voltage increases enough to
cause a trip.

BTW, does anyone have a smooth safe technique for using an automatic PAT
Tester on showers and ovens? Yes, I know it's a *portable appliance*
tester but...


--
roger

delete x's to email

In article , roger
writes

It is possible to have an appliance [or eg a shower] which works fine
but has a leak of a few ohms between neutral and earth.
This may not normally trip the RCD.
However, when a nearby kettle and the dishwasher are switched on and
draw 20Amps or so, the neutral-to-earth voltage increases enough to
cause a trip.


Thanks for the suggested explanation. However as I was the only one in
the house at the time, I can say with a high degree of certainty (*),
that nothing else got switched on either whilst the shower was trying to
be used, or the hob.

(*) the possible exception was the thermostat on the fridge cutting in.


Adrian
--
To Reply :
replace "news" with "adrian" and "nospam" with "ffoil"
Sorry for the rigmarole, If I want spam, I'll go to the shops
Every time someone says "I don't believe in trolls", another one dies.

Adrian Simpson writes
writes

It is possible to have an appliance [or eg a shower] which works fine
but has a leak of a few ohms between neutral and earth.
This may not normally trip the RCD.
However, when a nearby kettle and the dishwasher are switched on and
draw 20Amps or so, the neutral-to-earth voltage increases enough to
cause a trip.


Thanks for the suggested explanation. However as I was the only one in
the house at the time, I can say with a high degree of certainty (*),
that nothing else got switched on either whilst the shower was trying to
be used, or the hob.

(*) the possible exception was the thermostat on the fridge cutting in.

The last instance I had of this, the offender was a one-year-old Bosch
fridge.

An increase in N to E voltage due to load change in a neighbour's house
could presumably have the same effect.

If you ever find what it was/is causing your problem, do please post and
let us all know.

--
roger

In article , roger
writes
The last instance I had of this, the offender was a one-year-old Bosch
fridge.


The fridge is out of the ark (It was well past its first flush of your
when I got it, which will be 17 years this December), so I suppose that
could be starting to shown signs of old age.

If you ever find what it was/is causing your problem, do please post and
let us all know.


If I find out what it was, I will report back.


Adrian
--
To Reply :
replace "news" with "adrian" and "nospam" with "ffoil"
Sorry for the rigmarole, If I want spam, I'll go to the shops
Every time someone says "I don't believe in trolls", another one dies.

Yerrs Tony. But I have - lets see.

Two computers.
Two printers
Scanner
Two monitors
PC loudspakers.
PABX
Cisco router
Labgear distribution amplifier.
6 TV's
3 radios

...all of whach are permanently pluugedd in, and, because the remotes
work, probablly have RF filters across the incoming mains.

Plus a random selection of battery chargers and so on. Not to mention an
immersion heater and two electric cookers, two fridges and a deep
freeze, all also permamently on.

Plus 9 extrenal lights and a klargester down the garden, and 2 external
power sockets, that get a leetle moist occasionally...


30mA was nusiance tripping on load for a long time - no pattern to it -
just general earth neutral leakage it would seem. 100mA is rock solid.

I think 30mA is fine for a small house, but not a large one really.

If I recall correctly, 40mA will kill you, therefore RCD's are set to trip
at 30mA

The whole purpose of an RCD is to try to prevent people getting killed from
electrocution
installing a 100mA breaker, IMO is madness

The only reason I can see to use a 100mA breaker, would be to feed it's
output directly into several 30mA breakers to keep a handful of circuits
separate
(for example, mains in -100mA breaker, then this feeds to house 30mA
breaker and another 30mA breaker for another building.

I had a problem with an old MK ELCB - it would randomly trip for no apparent
reason
Turns out the breaker was knackered - It was replaced with the same
make/model/rating, and it hasn't tripped incorrectly since

Just my £0.02

Sparks...

In article ,
"Sparks" writes:

If I recall correctly, 40mA will kill you, therefore RCD's are set to trip
at 30mA

So can 30mA, but not normally within the time it takes for
an RCD to trip.

The whole purpose of an RCD is to try to prevent people getting killed from
electrocution

No, that's _one_ purpose.
Indeed RCD's used for providing protection against electrocution
must not exceed 30mA rating. However, RCD's protecting a whole
installation (due to excessive earth fault loop impedance) must be
at least 100mA, but cannot be used to provide protection against
electrocution. Hence a single RCD cannot do both jobs.

installing a 100mA breaker, IMO is madness

A direct swap is indeed silly. The installation was wrong before,
and is now wrong in a different (possibly more dangerous) way.

The only reason I can see to use a 100mA breaker, would be to feed it's
output directly into several 30mA breakers to keep a handful of circuits
separate
(for example, mains in -100mA breaker, then this feeds to house 30mA
breaker and another 30mA breaker for another building.

No, that doesn't work. RCD's don't discriminate on current.
You should avoid daisy chaining them at all, but if you have to,
the one nearer the supply has to be a time delayed type.

100mA and greater RCD's are for protection again high earth
impedance, where a short to earth might not pass enough current
to trip the fault current protective device within the required
time (or even at all). This is commonly the case where the system
uses an earth rod for earthing.

--
Andrew Gabriel

"Andrew Gabriel" wrote in message
...
In article ,
"Sparks" writes:

If I recall correctly, 40mA will kill you, therefore RCD's are set to
trip
at 30mA

So can 30mA, but not normally within the time it takes for
an RCD to trip.

The whole purpose of an RCD is to try to prevent people getting killed
from
electrocution

No, that's _one_ purpose.
Indeed RCD's used for providing protection against electrocution
must not exceed 30mA rating. However, RCD's protecting a whole
installation (due to excessive earth fault loop impedance) must be
at least 100mA, but cannot be used to provide protection against
electrocution. Hence a single RCD cannot do both jobs.

installing a 100mA breaker, IMO is madness

A direct swap is indeed silly. The installation was wrong before,
and is now wrong in a different (possibly more dangerous) way.

The only reason I can see to use a 100mA breaker, would be to feed it's
output directly into several 30mA breakers to keep a handful of circuits
separate
(for example, mains in -100mA breaker, then this feeds to house 30mA
breaker and another 30mA breaker for another building.

No, that doesn't work. RCD's don't discriminate on current.
You should avoid daisy chaining them at all, but if you have to,
the one nearer the supply has to be a time delayed type.

100mA and greater RCD's are for protection again high earth
impedance, where a short to earth might not pass enough current
to trip the fault current protective device within the required
time (or even at all). This is commonly the case where the system
uses an earth rod for earthing.

--
Andrew Gabriel

Hmmm, that's interesting.

One of my projects for Q1 next year (ie before the draconian new regs appear
and drive the cost up to the point where I won't bother) is to replace my cu
rrent CU.

I've read through a number of posts on the matter, and will be getting hold
of a 16th edition on-site guide soon, but initial plan was to install an
isolator before the CU, and replace the current one with one populated with
a mixture of RCBOs and MCBs, possibly splitting my office off onto it's own
ring, protected by an MCB due to the amount of computer equipment in there.

I had been uncertain as to whether the CU should have overall protection of
a time-delayed 100mA RCD, but from what you say this is probably not
necessary nor desireable. The earth is supplied by the provider.

Is this about the size of things?

cheers
Richard

--
Richard Sampson

email me at
richard at olifant d-ot co do-t uk

On Mon, 29 Sep 2003 14:21:37 +0100, "RichardS" noaccess@invalid
wrote:

One of my projects for Q1 next year (ie before the draconian new regs appear
and drive the cost up to the point where I won't bother) is to replace my cu
rrent CU.

One thing to be wary of is that the new regulations don't kick in with
a retrospective element.

By this I mean that when you eventually come to sell your house the
solicitors may wish you, as the seller, to confirm whether there has
been any electrical modifications made during your tenancy - and if so
to provide appropriate certification. It is already common for the
purchasers solicitor to issue a questionaire to the buyers solicitor
requesting confirmation of various services, neighbourhood disputes,
etc.

This particular question about the electrical installation could be
posed a number of ways, I suppose I would not be surprised if they
left out mention of 1st April 2004.

PoP

"PoP" wrote in message
...
On Mon, 29 Sep 2003 14:21:37 +0100, "RichardS" noaccess@invalid
wrote:

One of my projects for Q1 next year (ie before the draconian new regs
appear
and drive the cost up to the point where I won't bother) is to replace my
cu
rrent CU.

One thing to be wary of is that the new regulations don't kick in with
a retrospective element.

By this I mean that when you eventually come to sell your house the
solicitors may wish you, as the seller, to confirm whether there has
been any electrical modifications made during your tenancy - and if so
to provide appropriate certification. It is already common for the
purchasers solicitor to issue a questionaire to the buyers solicitor
requesting confirmation of various services, neighbourhood disputes,
etc.

This particular question about the electrical installation could be
posed a number of ways, I suppose I would not be surprised if they
left out mention of 1st April 2004.

PoP


Yup, noted, thanks.

It should be said that there are also quite a number of ways to answer a
question truthfully...


cheers
Richard

--
Richard Sampson

email me at
richard at olifant d-ot co do-t uk

On Mon, 29 Sep 2003 16:22:45 +0100, "RichardS" noaccess@invalid
wrote:

It should be said that there are also quite a number of ways to answer a
question truthfully...

I spy a budding politician and claim my five pounds

PoP

"PoP" wrote in message
...
On Mon, 29 Sep 2003 16:22:45 +0100, "RichardS" noaccess@invalid
wrote:

It should be said that there are also quite a number of ways to answer a
question truthfully...

I spy a budding politician and claim my five pounds

PoP


Public life? I think not! :-)

Just spent rather too much time (and money) in the company of lawyers
recently.... think some of it must have rubbed off. I obviously need
rehab...



--
Richard Sampson

email me at
richard at olifant d-ot co do-t uk

In article , tony sayer
writes
In article , Adrian Simpson
writes
I'm having a bit of "fun" with my electrical system at home, and would
appreciate any advice.

The system has a RCD between the meter and the consumer unit (not sure
why, it was there when I moved in, but it has proved useful). The earth
is a spike in the ground at the back of the house.

Thursday night just as I turned the shower on, the RCD tripped out. So
I found a torch and reset the trip in the dark. I tried the shower
again, and off went the power again. I concluded that the shower had
died (it is 10-12 years old, so that seemed a fair conclusion).

This evening (Saturday), I was busy cooking my evening meal (on an
electric hob), and after about 10 minutes, off goes the power. Having
been moving the wiring for the boiler earlier in the day, I wondered if
I had got something wrong on that, so I turned off the RCD for that on
the consumer unit, put the power back on, and went back to cooking. 5
minutes or so later (certainly not straight away), off goes the power
again. I turned off the hob (which is 15 months old, so should have
some life in it yet), reset the trip, then tried the other two rings,
and within a minute or so, off goes the power again. The good news is
that by now the spuds are done, so at least I can get something to eat.

Having eaten the spuds, and thought about it, I consulted my tame
electrician (Dad). One thought that crossed my mind was that after a
long dry summer, the earth spike could be making a bad contact (*), so
whilst it was a long shot, it was worth a try. So I slowly poured some
salty water round the spike, allowing it to soak in. I then tried the
hob again for 20 minutes or so, and this time it was fine.

(*) memories of tales of old phone systems not working until a bucket of
water was tipped over the earth lead.

So, is it a coincidence that watering the earth spike has got things
working ?. Is there anything else I should do (getting it looked at
professionally will be arranged next week) ?.


TIA

Adrian

The RCD has nothing to do with the earth as such. All it does is look at
the current into the protected circuits, on the live and checks that the
same comes back out on the neutral. Any imbalance i.e. leakage to earth
then it will trip the level needs to be about 15 ma or so..

Usual causes are leakage between heating elements to earth especially
cookers, immersion heaters, and anything which uses an enclosed heating
elements inside a metal case.

Another cause sometimes is if the earth and neutral are inadvertently
connected together anywhere. This will result in nuisance tripping when
the load on the system increases. Some of the current will be carried by
the earth rod and if you have made this a *better* earth then a part of
the fault current will now be diverted via this route back to the
substation and hence the imbalance between power in on the live and out
on the neutral will cause the trip to drop....



Firstly apologies for the amount of quote, but the thread has been
dormant for that long, I though it best to retain the context.

Having finally got a sparks in to have a look at it (long story), the
circuits were fully checked out, and given a clean bill of health.

The problem was eventually traced to being a touched earth/neutral on
the wiring that has been put in place for the oven (which has yet to be
fitted). These have now had the ends insulated. Light usage was not
enough to cause the circuit to trip, but heavy usage (hob or shower)
was.

So thanks again for the replies.


Adrian
--
To Reply :
replace "news" with "adrian" and "nospam" with "ffoil"
Sorry for the rigmarole, If I want spam, I'll go to the shops
Every time someone says "I don't believe in trolls", another one dies.