Reverse Polarity Mains Socket -- How Dangerous?
Andrew Thelwell
Note: This post is talking about UK (220-240V mains supply)
My girlfriend and I recently moved into our newly-purchased house. We
wanted to get the electric meter changed but when the guy came out to
do so, he reported a live reading on the neutral block in our meter
box. This was potentially dangerous, he said, and he called out the
mains engineers. They investigated and couldn't replicate the problem.
They asked if we'd experienced any problems in the house and we hadn't.
Since then we've had three occurrences of the RCDs in our fuse box
tripping. I today bought a standard socket tester and tested every
socket in the house. I've found the culprit to be the mains outlet in
our spare bedroom, which appears to be incorrectly wired, showing a
live/neutral reverse on the tester.
My questions, then...
1) Would this explain both the apparent live neutral reading in our
main meter box and the tripping of the RCDs? I always thought RCDs were
only concerned with earthing faults, not live/neutral reverse polarity
type problems
2) I've been using the sockets in that room with no real probles apart
from the trips. All equipment (TV, XBox, amplifier, phone charger) have
worked OK thus far. Is the socket likely to be causing any harm?
3) Is this potentially dangerous?
4) Is getting this fixed a big (and ergo, expensive) job?
Your help would be much appreciated as I've had surprising difficult
finding any info about this on the web.
Many thanks
Andy
R D S
"Andrew Thelwell" <andy.t...@gmail.com> wrote in message
news:1164567010.5...@h54g2000cwb.googlegroups.com...
> Hi,
>
>
> Since then we've had three occurrences of the RCDs in our fuse box
> tripping. I today bought a standard socket tester and tested every
> socket in the house. I've found the culprit to be the mains outlet in
> our spare bedroom, which appears to be incorrectly wired, showing a
> live/neutral reverse on the tester.
>
>
>
> Your help would be much appreciated as I've had surprising difficult
> finding any info about this on the web.
>
> Many thanks
>
> Andy
>
Would just swaping the wires in the plug socket sort it?
Andrew Gabriel
"Andrew Thelwell" <andy.t...@gmail.com> writes:
> Hi,
>
> Note: This post is talking about UK (220-240V mains supply)
>
> My girlfriend and I recently moved into our newly-purchased house. We
> wanted to get the electric meter changed but when the guy came out to
> do so, he reported a live reading on the neutral block in our meter
> box. This was potentially dangerous, he said, and he called out the
> mains engineers. They investigated and couldn't replicate the problem.
Well, it's not a problem that goes away by itself.
One of the engineers is wrong.
> They asked if we'd experienced any problems in the house and we hadn't.
>
> Since then we've had three occurrences of the RCDs in our fuse box
> tripping. I today bought a standard socket tester and tested every
> socket in the house. I've found the culprit to be the mains outlet in
> our spare bedroom, which appears to be incorrectly wired, showing a
> live/neutral reverse on the tester.
>
> My questions, then...
>
> 1) Would this explain both the apparent live neutral reading in our
> main meter box and the tripping of the RCDs? I always thought RCDs were
No, and No.
> only concerned with earthing faults, not live/neutral reverse polarity
> type problems
>
> 2) I've been using the sockets in that room with no real probles apart
> from the trips. All equipment (TV, XBox, amplifier, phone charger) have
> worked OK thus far. Is the socket likely to be causing any harm?
Not to the appliances.
> 3) Is this potentially dangerous?
Yes - there's no fuse in the live.
> 4) Is getting this fixed a big (and ergo, expensive) job?
It's easy, but this and and RCD trips indicate you should have the
installation inspected. I don't necessarily mean a full inspection
and test, but get an electrician in to give it a quick check, and
advise if anything more substantial is required.
--
Andrew Gabriel
David Hansen
<andy.t...@gmail.com> wrote this:-
>3) Is this potentially dangerous?
Yes.
>4) Is getting this fixed a big (and ergo, expensive) job?
a) switch off the main switch at the consumer unit. Check that the
lights on the socket tester are now out.
b) unscrew the socket.
c) unscrew the live and neutral wires from the terminals. These are
probably coloured red and black respectively, but may be coloured
brown and blue respectively. There will be one, two or three wires
to each terminal.
d) look at the back of the socket, where there will be terminals
marked L and N for the live and neutral wires.
e) back off the screws fully and then insert the wires into the
correct terminals.
f) check that all wires are secure, pushed in fully and will not
pull out. That includes the earth wires, which you should not have
touched.
g) screw the socket back, checking no wires are trapped. One wire to
each terminal is a lot easier to get back than three and a double
socket is easier than a single.
h) switch on and check the lights on the socket tester. Check the
other sockets.
i) have someone who knows how to do wring look over the
installation. Someone who couldn't be bothered to wire up a socket
correctly will not have bothered with any other work they did, or
tested it.
--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54
d...@gglz.com
a "live" reading on the neutral at the electricity meter. What exactly
did he mean by "live"? I doubt both phase(live) and neutral could be
sitting at 240V. Nor should it be responsible for RCD trips(which
happens because the current on the phase and neutral is different -
i.e. leaking somewhere).
In his position I would have flicked off the main isolater and to see
if the problem cleared, then switched on the MCB's one by one.
Significant voltage on the household neutral (which is what I think he
meant) would suggest to me that it is poorly tied to the suppliers
neutral - and I'd want that fixed urgently.
2) Yes, if a faulty piece of equipment was plugged in. Don't use that
socket
3) Yes, there is something odd happening and needs professional
investigation.
4) Probably not a major expense, if it's an isolated stupid mistake by
a professional or an isolated case of uninformed tinkering. If however
it's the tip of the iceberg of a rewire by a madman, then very urgent
and somewhat expensive work may be required.
d...@gglz.com
> correct terminals.
You're assuming it's a single isolated fault. Given that there's some
bizarre behaviour, I wouldn't do a quick fix until I was quite clear
about other possible faults.
John Rumm
> My questions, then...
>
> 1) Would this explain both the apparent live neutral reading in our
> main meter box and the tripping of the RCDs?
No, and no. Did your first engineer say what he was comparing the
neutral with to delcare it "live"?
(if it appeared live compared to the live conductor, then that would
suggest the polarity of your supply is incorrect (unlikely!), however if
he compared it to earth, it may tell you nothing of significance).
> I always thought RCDs were
> only concerned with earthing faults, not live/neutral reverse polarity
> type problems
This is true. They detect inbalance between the current flowing in the
neutral and live conductors.
> 2) I've been using the sockets in that room with no real probles apart
> from the trips. All equipment (TV, XBox, amplifier, phone charger) have
> worked OK thus far. Is the socket likely to be causing any harm?
> 3) Is this potentially dangerous?
In the normal course of operation it will not be explicitly dangerous -
many countries electrical systems do not maintain correct polarisation,
and yet they remain resonably safe. The real danger comes in the event
of a fault that causes the fuse to blow. Even with the fuse blown the
device could still remain "live"
> 4) Is getting this fixed a big (and ergo, expensive) job?
In itself (the reversed polarity) no, it is trivial. The RCD tripping
however could be due to any number of possible causes, and it will be
harder to identify the culprit.
> Your help would be much appreciated as I've had surprising difficult
> finding any info about this on the web.
There have been many threads on tracjing down the cause of spurious
trips on RCDs in this group in the past. It may be worth googling for a
few...
--
Cheers,
John.
/=================================================================\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\=================================================================/
David Hansen
<d...@gglz.com> wrote this:-
>You're assuming it's a single isolated fault.
Indeed. However, fixing this one fault means there is one less
problem to worry about.
>Given that there's some
>bizarre behaviour, I wouldn't do a quick fix until I was quite clear
>about other possible faults.
I don't see how fixing this one particular fault will make any
others worse.
d...@gglz.com
> I don't see how fixing this one particular fault will make any
> others worse.
What if phase, neutral and earth have all been rotated at both ends?
Maybe phase is connected to the neutral position at this socket and
earth to the live position (and all the colours are wrong because
they've been jumbled at the consumer unit end too).
I've actually seen this done on a boat. It was a corporate event, my
company had hired the yacht, and the skiper proudly gave me the
extension he had made up with a UK socket strip on one end and a schuko
on the other. I suspect he was red/green colour blind.
Ron
"Andrew Thelwell" <andy.t...@gmail.com> wrote in message
news:1164567010.5...@h54g2000cwb.googlegroups.com...
>
> Note: This post is talking about UK (220-240V mains supply)
>
> My girlfriend and I recently moved into our newly-purchased house. We
> wanted to get the electric meter changed but when the guy came out to
> do so, he reported a live reading on the neutral block in our meter
> box. This was potentially dangerous, he said, and he called out the
> mains engineers. They investigated and couldn't replicate the problem.
> They asked if we'd experienced any problems in the house and we hadn't.
>
certificate, so ask for a copy, then contact the person that arranged your
survey and complain. You can't have both live and neutral on a neutral
block or your main fuse would blow. What he has measured is the voltage
between neutral and earth. If you have fluorescent lights this sometimes
happens. It can happen if you have a faulty TV or video.
> Since then we've had three occurrences of the RCDs in our fuse box
> tripping. I today bought a standard socket tester and tested every
> socket in the house. I've found the culprit to be the mains outlet in
> our spare bedroom, which appears to be incorrectly wired, showing a
> live/neutral reverse on the tester.
>
That would not cause a problem anywhere else, but should have been checked
before you bought the house. The socket is not connected to anything else
unless it is in a loop. Just rewire it or get the seller to correct it.
> My questions, then...
>
> 1) Would this explain both the apparent live neutral reading in our
> main meter box and the tripping of the RCDs? I always thought RCDs were
> only concerned with earthing faults, not live/neutral reverse polarity
> type problems
>
Depending how it is wired and what you use might make one circuit breaker
trip.
> 2) I've been using the sockets in that room with no real probles apart
> from the trips. All equipment (TV, XBox, amplifier, phone charger) have
> worked OK thus far. Is the socket likely to be causing any harm?
>
It will not cause harm, but you will be switching the neutral instead of the
live.
> 3) Is this potentially dangerous?
>
Not unless you take something apart and think it is switched off !
> 4) Is getting this fixed a big (and ergo, expensive) job?
>
No, get a screwdriver - open the socket after witching the mains off and
make sure that the L terminal is going to RED or BROWN wires and N terminal
to BLACK or BLUE. If they are correct then check inside the consumer unit -
then check for any junction boxes.
>
> Your help would be much appreciated as I've had surprising difficult
> finding any info about this on the web.
>
> Many thanks
>
> Andy
>
There are lots of cowboys about, so don't be conned in to buying new
consumer units or having your home rewired. Don't bother checking for
reputable trades people with trading standards either - they don't bother
checking them out and are not allowed to tell the public even if a company
does have a bad record!
Adrian C
> He's a cowboy trying to rip you off. A new house should have an inspection
> certificate, so ask for a copy, then contact the person that arranged your
> survey and complain. You can't have both live and neutral on a neutral
> block or your main fuse would blow. What he has measured is the voltage
> between neutral and earth. If you have fluorescent lights this sometimes
> happens. It can happen if you have a faulty TV or video.
Sigh.... Just beware that 'ron' has a poor understanding of electricity
judged from previous ramblings in usenet, and is mostly trolling...
--
Adrian C
John Rumm
>>My girlfriend and I recently moved into our newly-purchased house. We
>>wanted to get the electric meter changed but when the guy came out to
>>do so, he reported a live reading on the neutral block in our meter
>>box. This was potentially dangerous, he said, and he called out the
>>mains engineers. They investigated and couldn't replicate the problem.
>>They asked if we'd experienced any problems in the house and we hadn't.
>>
>
> He's a cowboy trying to rip you off.
I can't see any basis for that conclusion.
> A new house should have an inspection
> certificate, so ask for a copy, then contact the person that arranged your
> survey and complain.
He never said the house was new, only that he purchased it recently.
> What he has measured is the voltage
> between neutral and earth.
You know this how?
> If you have fluorescent lights this sometimes
> happens. It can happen if you have a faulty TV or video.
It can also happen when the sky is cloudy. There is however equally
little connection between the observation and your suggested "cause"
>>Since then we've had three occurrences of the RCDs in our fuse box
>>tripping. I today bought a standard socket tester and tested every
>>socket in the house. I've found the culprit to be the mains outlet in
>>our spare bedroom, which appears to be incorrectly wired, showing a
>>live/neutral reverse on the tester.
>>
>
> That would not cause a problem anywhere else, but should have been checked
> before you bought the house.
Depends on what survey you paid for.
> The socket is not connected to anything else
> unless it is in a loop.
Which is highly likely...
>>My questions, then...
>>
>>1) Would this explain both the apparent live neutral reading in our
>>main meter box and the tripping of the RCDs? I always thought RCDs were
>>only concerned with earthing faults, not live/neutral reverse polarity
>>type problems
>>
>
> Depending how it is wired and what you use might make one circuit breaker
> trip.
What makes you say that?
Dave Plowman (News)
Andrew Thelwell <andy.t...@gmail.com> wrote:
> Note: This post is talking about UK (220-240V mains supply)
> My girlfriend and I recently moved into our newly-purchased house. We
> wanted to get the electric meter changed but when the guy came out to
> do so, he reported a live reading on the neutral block in our meter
> box. This was potentially dangerous, he said, and he called out the
> mains engineers. They investigated and couldn't replicate the problem.
> They asked if we'd experienced any problems in the house and we hadn't.
My feeling is to trust the engineers over a meter swapper. Those are
simply 'trained' for the one job and usually not even employees of the
electricity supplier.
> Since then we've had three occurrences of the RCDs in our fuse box
> tripping.
First, can you be clear about this? Most houses only have the one RCD in
the 'fuse box'. So do you mean MCBs (circuit breakers)? An RCD is easy to
spot - it has a test button on it.
> I today bought a standard socket tester and tested every
> socket in the house. I've found the culprit to be the mains outlet in
> our spare bedroom, which appears to be incorrectly wired, showing a
> live/neutral reverse on the tester.
I'm afraid that isn't the 'culprit' for anything.
> My questions, then...
> 1) Would this explain both the apparent live neutral reading in our
> main meter box and the tripping of the RCDs? I always thought RCDs were
> only concerned with earthing faults, not live/neutral reverse polarity
> type problems
No and no. RCDs aren't concerned with earth faults - they work by looking
for imbalance in the line and neutral current flow.
> 2) I've been using the sockets in that room with no real probles apart
> from the trips. All equipment (TV, XBox, amplifier, phone charger) have
> worked OK thus far. Is the socket likely to be causing any harm?
Unlikely.
> 3) Is this potentially dangerous?
Yes. A 13 amp lug fuse is in the line for a good reason. With this socket
it is effectively in the neutral.
> 4) Is getting this fixed a big (and ergo, expensive) job?
It *should* be merely a matter of swapping the wires to the socket.
> Your help would be much appreciated as I've had surprising difficult
> finding any info about this on the web.
Like all things you have to ask the right questions to get sensible
answers.
--
*The e-mail of the species is more deadly than the mail *
Dave Plowman da...@davenoise.co.uk London SW
To e-mail, change noise into sound.
m...@privacy.net
<andy.t...@gmail.com> wrote:
>Hi,
>
>Note: This post is talking about UK (220-240V mains supply)
>
>My girlfriend and I recently moved into our newly-purchased house. We
>wanted to get the electric meter changed but when the guy came out to
>do so, he reported a live reading on the neutral block in our meter
>box. This was potentially dangerous, he said, and he called out the
>mains engineers. They investigated and couldn't replicate the problem.
>They asked if we'd experienced any problems in the house and we hadn't.
<snip>
The house is newly purchased and obviously the electrics are
sub-standard/faulty. Take up the matter with the builder and get them
to come and do a full electrical test and remedy any faults.
chris...@postmaster.co.uk
Andrew Thelwell wrote:
> I today bought a standard socket tester and tested every
> socket in the house. I've found the culprit to be the mains outlet in
> our spare bedroom, which appears to be incorrectly wired, showing a
> live/neutral reverse on the tester.
When I encountered this once, it transpired that some of the sockets in
the house had their neutral/live terminals on left/right respectively
and some, presumably a different manufacture, had them the other way
round. The sparks had simply wired them all up the same way without
looking. A point to check when replacing a socket.
Chris
Andy Wade
> First, can you be clear about this? Most houses only have the one RCD in
> the 'fuse box'.
More than one RCD suggests that it might be a TT installation (i.e. it
has its own earth rod and doesn't rely on an earth connection provided
by the supply company). This could account for a variable voltage
reading between the supply neutral and the local earth.
Is the house out in the sticks and fed via a long overhead line?
--
Andy
Guy King
from <m...@privacy.net> contains these words:
> The house is newly purchased and obviously the electrics are
> sub-standard/faulty. Take up the matter with the builder and get them
> to come and do a full electrical test and remedy any faults.
Newly purchased doesn't necessarily mean newly built.
--
Skipweasel
Pay no attention to that man behind the curtain.
Andrew Thelwell
First off thanks for all the replies -- great to get so much feedback.
Let me clarify a few points... this should help with the discussion:
1) The house is newly-purchased, not a new build. It's a 1930's
semi-detached
2) I may have misled when I referred to RCDs (sorry!). We have two
large rotary switch type things on our consumer unit labelled
"Earth-Leakage Circuit Breaker". There is apparently one on each 'loop'
of the house. It is these that have tripped
3) The problem with the meter when the guy came to change it was that
he was as follows: He had one of those 'mains tester' screwdrivers with
the LEDs in the end that should only light up on when touched to a live
terminal. However, he got it to light up on ALL FOUR terminals attached
to our meter (+ in, - in, + out, - out, yes?). I don't think there was
an suggestion as to the 'size' of the current though. He also got it to
light up when he pressed it to the big grey block (neutral block) in
the meter box, which apparently it shouldn't do. This happenend both
with our consumer unit main isolator turned ON and OFF. It stopped,
however, when he pulled the main fuse out of the meter box.
Two mains engineers from Central Networks came out that night and
tested thoroughly for almost 2 hours in our meter box and around our
roof (we have overhead supply). They found nothing out of place at all.
They asked if we'd experienced any oddities inside the house, which we
hadn't. However, since then we have seen our Earth-Leakage Circuit
Breakers (not RCDs, sorry!) trip three times. Two of these times have
been due to turning on the one socket in the spare room. One other time
the other ELCB tripped when my girlfriend turned on the microwave. All
sockets in the house test out fine using a normal B&Q socket tester,
except the one in the spare room, which shows only one light,
supposedly "L/N Reverse".
Hope this helps -- your further feedback would be much appreciated
based on these additional details.
Thanks!
Andy
meow...@care2.com
> Hi all, I'm the OP,
>
> First off thanks for all the replies -- great to get so much feedback.
>
> Let me clarify a few points... this should help with the discussion:
>
> 1) The house is newly-purchased, not a new build. It's a 1930's
> semi-detached
>
> 2) I may have misled when I referred to RCDs (sorry!). We have two
> large rotary switch type things on our consumer unit labelled
> "Earth-Leakage Circuit Breaker".
Ohhhhhhhhhhhhhhhh. Those. In that case we know a couple of things
straight away. This is oldish wiring, and uses TT earthing, meaning a
local earth rod with high earth impedance.
> There is apparently one on each 'loop'
> of the house.
Big house then?
> It is these that have tripped
ELCBs rarely trip in error. I think I know whats going on now.
> 3) The problem with the meter when the guy came to change it was that
> he was as follows: He had one of those 'mains tester' screwdrivers with
> the LEDs in the end that should only light up on when touched to a live
> terminal. However, he got it to light up on ALL FOUR terminals attached
> to our meter (+ in, - in, + out, - out, yes?). I don't think there was
> an suggestion as to the 'size' of the current though. He also got it to
> light up when he pressed it to the big grey block (neutral block) in
> the meter box, which apparently it shouldn't do. This happenend both
> with our consumer unit main isolator turned ON and OFF. It stopped,
> however, when he pulled the main fuse out of the meter box.
OK, then we can safely ignore anything he says
> Two mains engineers from Central Networks came out that night and
> tested thoroughly for almost 2 hours in our meter box and around our
> roof (we have overhead supply). They found nothing out of place at all.
And we can safely conclude nothing is out of place at all with your
supply as far as the CU or fusebox.
> They asked if we'd experienced any oddities inside the house, which we
> hadn't. However, since then we have seen our Earth-Leakage Circuit
> Breakers (not RCDs, sorry!) trip three times. Two of these times have
> been due to turning on the one socket in the spare room. One other time
> the other ELCB tripped when my girlfriend turned on the microwave. All
> sockets in the house test out fine using a normal B&Q socket tester,
> except the one in the spare room, which shows only one light,
> supposedly "L/N Reverse".
OK, I think I see the problem clearly. An ELCB will trip when it sees
large earth currents (unlike RCDs which trip on small earth currents).
This means you have a major fault in whatever appliance caused it to
trip when the socket was switched on. So the microwave and whatever was
plugged into the spare room socket should be taken out of service now,
and some checks done on them later to confirm or deny theyre the
problem.
>From everything you say, the only problem with the installation itself
is the swapped wires behind a socket, which is a trivial matter easily
fixed in 2 minutes.
Your 2 faulty appliances would not have tripped anything at your last
house, which I can conclude had low impedance earthing and no RCD.
However on a high impedance earth, which you have here, such faulty
appliances are not safe to use at all.
NT
meow...@care2.com
> Hope this helps -- your further feedback would be much appreciated
> based on these additional details.
>
> Thanks!
>
> Andy
Which brings us to the next question, how best to test your probably
faulty appliances. A low cost multimeter can be used to test resistance
from E to L&N pins on the plug, while its not plugged in, and any
controls on the item are set to on. However if the thing has any
electronic power controls, as many appliances now do, this wont test it
fully. Plugging an item into an RCD into a socket would quickly detect
any appliance with an earth leakage fault. Since it looks like you've
got at least 2 bad appliances, I'd get an RCD plug, make it into a
short extension lead, and have it to test things with.
Its a minor plus that youve got ELCBs and not an RCD, or you'd have had
bigger problems.
NT
d...@gglz.com
I think you have an older TT installation. This means because your
supply comes in on overhead wires, the earth is provided by you - the
customer, and not by the electricity company (who only supply live and
neutral).
Because customer supplied earths are considered less reliable, slightly
more elaborate protection is provided at the consumer unit (hence your
2 ELCB's).
However ELCB's are the older way of doing it. Now they use RCD's -
which are considered more reliable. (Basically an RCD will work
correctly regardless of how good or bad your earth is, whilst an ELCB
may not).
One option available is a replacement consumer unit with appropriate
RCD's (TT installations usually have 2, one less sensitive one for the
whole house, followed by a second more sensitive one just for the ring
mains).
Another option is to have the TT supply upgraded to TN-C-S (also known
as PME) as well as a simpler single RCD consumer unit (IMO this is the
better option).
Either way I would still have your installation checked out by a
professional, and your earth tested (check they are able to do this).
Regarding the dodgy socket - it could have all 3 wires transposed (live
is connected to neutral, earth to live, and neutral to earth). This
would explain why very low powered devices could be plugged in and work
ok (because they usually don't pass enough current to trip the ELCB),
but anything larger does.
Bear in mind some plug-in socket testers are unable to detect
earth/neutral transposition.
d...@gglz.com
> large earth currents (unlike RCDs which trip on small earth currents).
> This means you have a major fault in whatever appliance caused it to
> trip when the socket was switched on. So the microwave and whatever was
> plugged into the spare room socket should be taken out of service now,
> and some checks done on them later to confirm or deny theyre the
> problem.
It could still be a fault on that socket - and the devices are
performing correctly.
For instance, the microwave could just happened to have been switched
on just as the device on the faulty socket decided to draw more power
(e.g. a phone charger cycling).
A low power device may just be apparently working ok, even though it's
passing current between live and earth (because of faulty household
wiring) - just not quite enough to trip the ELCB all the time.
However if always operating the microwave on a believed good socket
causes a trip, then your explanation and not mine becomes the prime
suspect.
David Hansen
<d...@gglz.com> wrote this:-
>> I don't see how fixing this one particular fault will make any
>> others worse.
>
>What if phase, neutral and earth have all been rotated at both ends?
Then the socket tester would have indicated faults with most of the
other sockets.
David Hansen
<andy.t...@gmail.com> wrote this:-
>2) I may have misled when I referred to RCDs (sorry!). We have two
>large rotary switch type things on our consumer unit labelled
>"Earth-Leakage Circuit Breaker".
Do these things look as if they are 30 years old, or more recent?
>There is apparently one on each 'loop'
>of the house. It is these that have tripped
What do you mean by 'loop'?
Could you put a photograph of the above and the consumer unit on the
web somewhere?
>3) The problem with the meter when the guy came to change it was that
>he was as follows: He had one of those 'mains tester' screwdrivers with
>the LEDs in the end that should only light up on when touched to a live
>terminal.
Notoriously unreliable gadgets, largely useless.
d...@gglz.com
> Then the socket tester would have indicated faults with most of the
> other sockets.
Not if it was a spur.
(which is most likely for a badly wired add-on)
Andrew Thelwell
Thanks for the further feedback.
A few more responses:
1) I would doubt that the appliances in the spare room are faulty, to
be honest. They are all very new items: an LCD TV, XBOX 360, amplifier,
laptop... all new or nearly new (nothing older than 18 months). The
socket in that room shows up reversed on my plug-in tester but apart
from twice tripping the ELCB, everything works just fine.
2) The ELCBs look like they may be anything up to 30 years old -- they
don't have a modern look to them, although I've tested them both and
they work fine. I'll try to put up a photo online later. One controls
the kitchen sockets and lights, while the other covers everything else
in the house.
3) The microwave has tripped the kitchen ELCB once and once only when
being turned ON. The 'reversed' spare room socket has (so far) caused
two trips of the other ELCB - once when turning ON the switch (even
though no appliance were actually in operation, although I guess the
LCD TV and XBOX may draw power right away as they have 'stand by' type
function, yes?). The other time it tripped, it was when I turned the
socket OFF (after charging a battery in there for 24 hours+). Does this
give more clues?
4) My plug-in mains tester does not detect earth-neutral transposition
explicitly (it doesn't have it as an option)
Thanks,
Andy
John Rumm
> Andrew Thelwell wrote:
>
>
>>Hi all, I'm the OP,
>>
>>First off thanks for all the replies -- great to get so much feedback.
>>
>>Let me clarify a few points... this should help with the discussion:
>>
>>1) The house is newly-purchased, not a new build. It's a 1930's
>>semi-detached
>>
>>2) I may have misled when I referred to RCDs (sorry!). We have two
>>large rotary switch type things on our consumer unit labelled
>>"Earth-Leakage Circuit Breaker".
>
>
> Ohhhhhhhhhhhhhhhh. Those. In that case we know a couple of things
> straight away. This is oldish wiring, and uses TT earthing, meaning a
> local earth rod with high earth impedance.
Yup...
In fact at that age you may find that there is no dedicated earth at
all. Our house was wired in a similar way once, and the only earth was
provided by the gas pipe. It may be worth checking where the earth wires
from the CU (or ELCB if they are external to the CU) go to.
>>It is these that have tripped
> ELCBs rarely trip in error. I think I know whats going on now.
They can however be sensitized by leakage from a faulty applicance such
that they are prompted to trip when a non faulty appliance with a small
legitimate earth leakage (such as a bit of computer kit with RFI filter
on the mains input) is connected.
With a ELCB the liklihood of a trip will also increase as the weather
gets wetter, since this will tend to loawer the earth impedance of
whatever you are using as an earth.
>>3) The problem with the meter when the guy came to change it was that
>>he was as follows: He had one of those 'mains tester' screwdrivers with
>>the LEDs in the end that should only light up on when touched to a live
>>terminal. However, he got it to light up on ALL FOUR terminals attached
>>to our meter (+ in, - in, + out, - out, yes?). I don't think there was
>>an suggestion as to the 'size' of the current though. He also got it to
>>light up when he pressed it to the big grey block (neutral block) in
>>the meter box, which apparently it shouldn't do. This happenend both
>>with our consumer unit main isolator turned ON and OFF. It stopped,
>>however, when he pulled the main fuse out of the meter box.
>
>
> OK, then we can safely ignore anything he says
Yup... I am supprised that somone doing this type of job is trusting his
life to one of those toy screwdrivers!
>>Two mains engineers from Central Networks came out that night and
>>tested thoroughly for almost 2 hours in our meter box and around our
>>roof (we have overhead supply). They found nothing out of place at all.
>
>
> And we can safely conclude nothing is out of place at all with your
> supply as far as the CU or fusebox.
>
>
>
>>They asked if we'd experienced any oddities inside the house, which we
>>hadn't. However, since then we have seen our Earth-Leakage Circuit
>>Breakers (not RCDs, sorry!) trip three times. Two of these times have
>>been due to turning on the one socket in the spare room. One other time
>>the other ELCB tripped when my girlfriend turned on the microwave. All
>>sockets in the house test out fine using a normal B&Q socket tester,
>>except the one in the spare room, which shows only one light,
>>supposedly "L/N Reverse".
Andrew, what sort of wiring is there in the house? Modern PVC clad stuff
or old rubber or rubber/fabric coated stuff?
> OK, I think I see the problem clearly. An ELCB will trip when it sees
> large earth currents (unlike RCDs which trip on small earth currents).
> This means you have a major fault in whatever appliance caused it to
> trip when the socket was switched on. So the microwave and whatever was
> plugged into the spare room socket should be taken out of service now,
> and some checks done on them later to confirm or deny theyre the
> problem.
>
>>From everything you say, the only problem with the installation itself
> is the swapped wires behind a socket, which is a trivial matter easily
> fixed in 2 minutes.
I would tend to agree - the socket polarity fault sounds like it is not
directly related to the tripping problem.
> Your 2 faulty appliances would not have tripped anything at your last
> house, which I can conclude had low impedance earthing and no RCD.
> However on a high impedance earth, which you have here, such faulty
> appliances are not safe to use at all.
Note that the faulty appliance could be a fixed one like an immersion
heater, electric shower, cooker element etc - i.e. things that came with
the new house rather than one brought with.
(things with heating elements are prime candidates for high earth leakage)
David Hansen
<andy.t...@gmail.com> wrote this:-
>2) The ELCBs look like they may be anything up to 30 years old -- they
>don't have a modern look to them, although I've tested them both and
>they work fine. I'll try to put up a photo online later. One controls
>the kitchen sockets and lights, while the other covers everything else
>in the house.
I'll be interested in the photographs. My initial thought was that
they might be voltage operated devices, but it would be difficult to
install two in one installation.
>4) My plug-in mains tester does not detect earth-neutral transposition
>explicitly (it doesn't have it as an option)
AFAIAA none of them do, because it would be difficult to do in a
cheap bit of equipment.
David Hansen
<see.my.s...@nowhere.null> wrote this:-
>> OK, then we can safely ignore anything he says
>
>Yup... I am supprised that somone doing this type of job is trusting his
>life to one of those toy screwdrivers!
Presumably that is the level of training they get now.
Dave Plowman (News)
Andrew Thelwell <andy.t...@gmail.com> wrote:
> 3) The problem with the meter when the guy came to change it was that
> he was as follows: He had one of those 'mains tester' screwdrivers with
> the LEDs in the end that should only light up on when touched to a live
> terminal. However, he got it to light up on ALL FOUR terminals attached
> to our meter (+ in, - in, + out, - out, yes?). I don't think there was
> an suggestion as to the 'size' of the current though. He also got it to
> light up when he pressed it to the big grey block (neutral block) in
> the meter box, which apparently it shouldn't do. This happenend both
> with our consumer unit main isolator turned ON and OFF. It stopped,
> however, when he pulled the main fuse out of the meter box.
Neon screwdrivers are notoriously unreliable. However, with an overhead
supply it's quite common to have a few volts from neutral to true earth,
and that's what his screwdriver was seeing.
--
*When companies ship Styrofoam, what do they pack it in? *
meow...@care2.com
> Because customer supplied earths are considered less reliable, slightly
> more elaborate protection is provided at the consumer unit (hence your
> 2 ELCB's).
>
> However ELCB's are the older way of doing it. Now they use RCD's -
> which are considered more reliable. (Basically an RCD will work
> correctly regardless of how good or bad your earth is, whilst an ELCB
> may not).
No, an elcb doesnt care how bad the earth impedance is, it will still
work. And even old ELCBs are still orders of magnitude more reliable
than rcds.
> One option available is a replacement consumer unit with appropriate
> RCD's (TT installations usually have 2, one less sensitive one for the
> whole house, followed by a second more sensitive one just for the ring
> mains).
this wont solve anything
> Another option is to have the TT supply upgraded to TN-C-S (also known
> as PME) as well as a simpler single RCD consumer unit (IMO this is the
> better option).
nor will this. A single RCD CU is th worst possible optoin in fact, and
will cause the OP even more trouble.
> Either way I would still have your installation checked out by a
> professional, and your earth tested (check they are able to do this).
earth impedance testing is an easy diy job, and is cheap to do. Not
sure that it would be especially useful though.
> Regarding the dodgy socket - it could have all 3 wires transposed (live
> is connected to neutral, earth to live, and neutral to earth). This
> would explain why very low powered devices could be plugged in and work
> ok (because they usually don't pass enough current to trip the ELCB),
> but anything larger does.
N/E swaps would fit the symptoms, so would leaky appliances, and less
likely one or 2 other possible faults. I think time for some house-wide
testing, once the socket polarity swaps are sorted. Such testing is
simple to diy.
1 I'd open the Cu and visually check there are no L/N or N/E swaps.
2 I'd check all the sockets for the same thing.
3 I'd insulation test all appliances with a multimeter
4 I'd insulation test fixed items like immersion heater, oven, shower.
If by then the problems havent been sorted I'd be fairly surprised.
NB if the wiring is rubber, dont do 1 or 2, as sisturbing rubber wiring
tends to cause major problems.
NT
meow...@care2.com
> Hi, OP here again,
>
> Thanks for the further feedback.
>
> A few more responses:
>
> 1) I would doubt that the appliances in the spare room are faulty, to
> be honest. They are all very new items: an LCD TV, XBOX 360, amplifier,
> laptop... all new or nearly new (nothing older than 18 months). The
> socket in that room shows up reversed on my plug-in tester but apart
> from twice tripping the ELCB, everything works just fine.
Theres something more going on if that skt trips the elcb. Fix the
socket polarity swap first, test your appliances for earth leakage.
Either a leaky appliance (you have a lot of faith in new goods), a
miswired exntesion lead or a n/e swap.
> 2) The ELCBs look like they may be anything up to 30 years old -- they
> don't have a modern look to them, although I've tested them both and
> they work fine. I'll try to put up a photo online later. One controls
> the kitchen sockets and lights, while the other covers everything else
> in the house.
photo might tell us if theyre i or v operated, which would help.
> 3) The microwave has tripped the kitchen ELCB once and once only when
> being turned ON. The 'reversed' spare room socket has (so far) caused
> two trips of the other ELCB - once when turning ON the switch (even
> though no appliance were actually in operation, although I guess the
> LCD TV and XBOX may draw power right away as they have 'stand by' type
> function, yes?). The other time it tripped, it was when I turned the
> socket OFF (after charging a battery in there for 24 hours+). Does this
> give more clues?
yes, but nothing definitive.
NT
Andrew Gabriel
ELCB's frequently trip in error conditions outside the
house, over which the householder has no control, such
as overlapping earth resistance areas, and other causes
of external ground currents (lightning being a common
one, and someone else's earth leakage being another).
This is why they have a bad reputation for false trips.
--
Andrew Gabriel
Guy King
from meow...@care2.com contains these words:
> No, an elcb doesnt care how bad the earth impedance is, it will still
> work.
Provided it's lower than about 8k ohms!
Andrew Thelwell
I've put up a photo of our consumer unit and a close-up of one of the
ELCB's.
They can be found here:
http://www.andythelwell.com/cu.jpg
http://www.andythelwell.com/elcb.jpg
both are high-res photos
Your help is appreciated!
Thanks!
Andy
Andrew Gabriel
"Andrew Thelwell" <andy.t...@gmail.com> writes:
> Hello again all,
>
> I've put up a photo of our consumer unit and a close-up of one of the
> ELCB's.
>
> They can be found here:
>
> http://www.andythelwell.com/cu.jpg
> http://www.andythelwell.com/elcb.jpg
>
> both are high-res photos
They are RCD's, not [voltage operated] ELCB's.
RCD's were originally called current operated ELCB's (14th Ed Regs),
but that name didn't stick.
--
Andrew Gabriel
Andrew Gabriel
Come to think of it, the other give-away is that you can't
have multiple [voltage operated] ELCB's on one installation.
--
Andrew Gabriel
Guy King
from "Andrew Thelwell" <andy.t...@gmail.com> contains these words:
> I've put up a photo of our consumer unit and a close-up of one of the
> ELCB's.
This house of your - the roof timbers haven't got "The Ark" burnt into
them somwhere, have they?
meow...@care2.com
> In article <1164666488.1...@j44g2000cwa.googlegroups.com>,
> "Andrew Thelwell" <andy.t...@gmail.com> writes:
> > I've put up a photo of our consumer unit and a close-up of one of the
> > ELCB's.
> > http://www.andythelwell.com/cu.jpg
> > http://www.andythelwell.com/elcb.jpg
> They are RCD's, not [voltage operated] ELCB's.
> RCD's were originally called current operated ELCB's (14th Ed Regs),
> but that name didn't stick.
...and this changes everything. Any appliance you plug in that trips it
is liable to be leaky, but no guarantee its that one. I had assumed
they were voltage operated elcbs. Get used to trips and having to throw
out appliances that work ok.
NT
Dave Plowman (News)
<meow...@care2.com> wrote:
> No, an elcb doesnt care how bad the earth impedance is, it will still
> work. And even old ELCBs are still orders of magnitude more reliable
> than rcds.
You jest? We used to use them on 'The Bill' camera setup when running from
mains, (obviously). If the camera touched anything vaguely conductive it
would trip. Even just setting it down on the ground.
--
*How do you tell when you run out of invisible ink? *
Andrew Thelwell
meow...@care2.com
> The message <1164663838.0...@45g2000cws.googlegroups.com>
> from meow...@care2.com contains these words:
> > No, an elcb doesnt care how bad the earth impedance is, it will still
> > work.
> Provided it's lower than about 8k ohms!
of cours, yes, you do have to have an earth connection.
NT
meow...@care2.com
> In article <1164663838.0...@45g2000cws.googlegroups.com>,
> <meow...@care2.com> wrote:
> > No, an elcb doesnt care how bad the earth impedance is, it will still
> > work. And even old ELCBs are still orders of magnitude more reliable
> > than rcds.
> You jest? We used to use them on 'The Bill' camera setup when running from
> mains, (obviously). If the camera touched anything vaguely conductive it
> would trip. Even just setting it down on the ground.
And how is this the fault of the elcb, what mechanism are you
proposing? It seems clear you had a faulty installation. I'd rule out a
major camera wiring fault as you'd have felt that :)
ELCBs work by sensing the voltage difference between mains earth rod
and a separate sense electrode placed elsewhere in the ground. For
30-50v pd to be reached, which is needed to trip an elcb, you have to
have a fairly large current flow down the mains earth wire. If touching
a camera to anything trips an elcb, there is something very wrong with
your setup. The big plus of ELCBs is that of all earth leakage
protection devices they are the least liable to nuisance trips. Theyre
not perfect, but theyre orders of magnitude less problematic than RCDs.
NT
meow...@care2.com
> In article <1164622691.0...@45g2000cws.googlegroups.com>,
> Andrew Thelwell <andy.t...@gmail.com> wrote:
> > 3) The problem with the meter when the guy came to change it was that
> > he was as follows: He had one of those 'mains tester' screwdrivers with
> > the LEDs in the end that should only light up on when touched to a live
> > terminal. However, he got it to light up on ALL FOUR terminals attached
> > to our meter (+ in, - in, + out, - out, yes?). I don't think there was
> > an suggestion as to the 'size' of the current though. He also got it to
> > light up when he pressed it to the big grey block (neutral block) in
> > the meter box, which apparently it shouldn't do. This happenend both
> > with our consumer unit main isolator turned ON and OFF. It stopped,
> > however, when he pulled the main fuse out of the meter box.
> Neon screwdrivers are notoriously unreliable. However, with an overhead
> supply it's quite common to have a few volts from neutral to true earth,
> and that's what his screwdriver was seeing.
Neons have a strike voltage in the region of 80v, so it is not possible
for them to light on N-E voltage. The meter swapper was seeing
capacitive leakage from mains wiring to the ladder, through him and the
screwdriver, to anything he touched. The neon lighting was meaningless
in this case.
NT
Roger R
<meow...@care2.com> wrote in message
news:1164629367.8...@h54g2000cwb.googlegroups.com...
> Andrew Thelwell wrote:
>> 2) I may have misled when I referred to RCDs (sorry!). We have two
>> large rotary switch type things on our consumer unit labelled
>> "Earth-Leakage Circuit Breaker".
>
> Ohhhhhhhhhhhhhhhh. Those. In that case we know a couple of things
> straight away. This is oldish wiring, and uses TT earthing, meaning a
> local earth rod with high earth impedance.
>
I cannot see Andrews post (above) on my server (Clara)
I can see it using Google groups.
AFAIK all the other posts in the thread are visible including Andrews later
ones with the photo references, so what is going wrong for me and this
particular post of Andrew?
An interesting thread by the way.
Roger
Andrew Thelwell
Thanks all for your feedback.
This morning I rewired the socket. It was simply transposed (red wire
wired to neutral, black to live). I've swapped them, tested the socket,
and all is OK. So that's that one sorted.
I've been looking back over all your posts and been trying to work out
what the balance of opinion was with regard to whether or not this may
have had something to do with a) the meter man's odd readings and b)
the trips on our current-operated ELCBs (RCDs).
Am I right in saying, then, that this particular socket was almost
certainly not to blame for the odd readings by the meter man?
Am I also right in saying that his concerns, based on the lighting up
of his indicator screwdriver tool, were not necessarily very accurate?
Finally, am I also right in saying that this issue is probably not the
root cause of the RCD/ELCB trips?
Sorry if it appears I'm repeating myself, I'm just trying to get a
clear summary understanding of all the posts thus far.
Thanks,
Andy
David Hansen
<andy.t...@gmail.com> wrote this:-
>Am I right in saying, then, that this particular socket was almost
>certainly not to blame for the odd readings by the meter man?
Was anything plugged into it at the time he came with his
screwdriver? If nothing was then it is extremely unlikely, if
something was then there is a slight possibility if it has some sort
of electronics in it.
>Am I also right in saying that his concerns, based on the lighting up
>of his indicator screwdriver tool, were not necessarily very accurate?
Not very accurate at all, to the point of wondering why he bothered.
The real sparks who came later would have found any fault, assuming
it was not something intermittent.
>Finally, am I also right in saying that this issue is probably not the
>root cause of the RCD/ELCB trips?
Yes. The cause of these needs further investigation.
meow...@care2.com
The neon screwdriver indications are worthless, and the conclusions he
drew from them incorrect.
The socket wires transposed has nothing to do with the RCD trips you've
had.
AFAICS the only problem you've got now is rcd tripping, and thats a
commonish problem with rcds. The next move is to insulation test all
your appliances with a multimeter.
NT
John Rumm
> This morning I rewired the socket. It was simply transposed (red wire
> wired to neutral, black to live). I've swapped them, tested the socket,
> and all is OK. So that's that one sorted.
One less variable to worry about then...
> I've been looking back over all your posts and been trying to work out
> what the balance of opinion was with regard to whether or not this may
> have had something to do with a) the meter man's odd readings and b)
> the trips on our current-operated ELCBs (RCDs).
From the pictures it seems as if you do have a RCD - although a
resonably old design.
> Am I right in saying, then, that this particular socket was almost
> certainly not to blame for the odd readings by the meter man?
Yes, I think so.
> Am I also right in saying that his concerns, based on the lighting up
> of his indicator screwdriver tool, were not necessarily very accurate?
It is very unsafe to rely on indications from these things. They light
up any time you stick enough voltage across them and they pass negligble
current. Hence it is easy to get spurious results simply from a wire
that is capacitively coupled to another one, or worse, from your body
being coupled to something live by the same mechanism. This can result
in you appearing live to the base of the screwdriver. So touch the tip
to a live thing (i.e. same potential as you) and it does not light,
touch it to a neutral conductor and it does. Get it so that you are
hanging about with a coupled or induced voltage of about 100V and
everything looks live!
> Finally, am I also right in saying that this issue is probably not the
> root cause of the RCD/ELCB trips?
Yup. You have either faulty wiring (unlikely unless it is old rubber
stuff) or more likely one or more faulty appliances.
Andy Wade
> Neons have a strike voltage in the region of 80v, so it is not possible
> for them to light on N-E voltage.
Well that does rather depend on the value of N-E voltage...
But why is everyone assuming that the tool used was a neon screwdriver?
Andrew said:
>> ... one of those 'mains tester' screwdrivers with the LEDs in the
>> end that should only light up on when touched to a live terminal.
I assumed it was a 'voltstick' since LEDs were mentioned, and the
uninitiated might not realise that it wasn't a screwdriver and didn't
require contact. A voltstick, as most readers will know, will light up
when a butterfly flaps its wings in New Zealand.
I'd be very surprised indeed if meter fitters were being issued with
neon screwdrivers.
--
Andy
Andy Wade
> ELCBs work by sensing the voltage difference between mains earth rod
> and a separate sense electrode placed elsewhere in the ground.
I've never known that type of device to be fitted in a house. The usual
type of old ELCB (typified by that black Crabtree thing) had a low
impedance coil and was wired in series with the earthing conductor -
i.e. between the main earth terminal and the earth electrode. They were
rated in terms of a tripping current, 30 mA, and the winding impedance
was such that the coil voltage drop to trip was around 6 V. Their major
disadvantages were (a) that the coil could easily become shorted (or
partially shunted) by parallel earth paths, causing loss of protection,
and (b) that they could (and would) suffer from nuisance trips from
faults outside the installation - e.g. as a result of overlapping earth
resistance areas with neighbouring premises.
> If touching a camera to anything trips an elcb, there is something
> very wrong with your setup.
Example of problem (b) above, perhaps.
> The big plus of ELCBs is that of all earth leakage protection devices
> they are the least liable to nuisance trips. Theyre not perfect, but
> theyre orders of magnitude less problematic than RCDs.
That's just complete and utter bollocks. RCDs are an order of magnitude
more reliable than old ELCBs and have the advantage of providing shock
protection against direct as well as indirect contact.
--
Andy
Andrew Gabriel
Andy Wade <spamb...@ajwade.clara.co.uk> writes:
> meow...@care2.com wrote:
>
>> ELCBs work by sensing the voltage difference between mains earth rod
>> and a separate sense electrode placed elsewhere in the ground.
>
> I've never known that type of device to be fitted in a house. The usual
> type of old ELCB (typified by that black Crabtree thing) had a low
> impedance coil and was wired in series with the earthing conductor -
> i.e. between the main earth terminal and the earth electrode. They were
> rated in terms of a tripping current, 30 mA, and the winding impedance
> was such that the coil voltage drop to trip was around 6 V. Their major
Andy, sorry but I disagree. I have never seen a voltage operated
ELCB which has an earth current rating, as you suggest. I have a
couple (removed from homes and light commercial premises), and have
seen many still in use. Of course, since the coil has a resistance,
ohms law will dictate that there is a tripping current as well as
a tripping voltage, but that's not how the devices are intended to
work. They don't expect to see all the current associated with any
earth leakage in the first place, so a current rating makes no sense.
> disadvantages were (a) that the coil could easily become shorted (or
> partially shunted) by parallel earth paths, causing loss of protection,
No, this doesn't cause loss loss of protection (unless the coil
sense electrode has an overlapping earth resistance area). You
can have as many parallel earth paths as you like (see diagram
in 14th edition regs). If you have enough, the ELCB will stop
working, but this is because it has ceased to be necessary, and
is not an error situation (it is explicitly allowed for in the
testing procedure). In this case, and earth leakage will either
trip the fault current protection or remain safe (CPC not raised
as much as 50V above real earth).
> and (b) that they could (and would) suffer from nuisance trips from
> faults outside the installation - e.g. as a result of overlapping earth
> resistance areas with neighbouring premises.
Yes, that was a big problem.
>> The big plus of ELCBs is that of all earth leakage protection devices
>> they are the least liable to nuisance trips. Theyre not perfect, but
>> theyre orders of magnitude less problematic than RCDs.
>
> That's just complete and utter bollocks. RCDs are an order of magnitude
> more reliable than old ELCBs and have the advantage of providing shock
> protection against direct as well as indirect contact.
Agree completely.
--
Andrew Gabriel
meow...@care2.com
You illustrate the first problem with elcbs, namely that there is more
than one type of device referred to as an ELCB. There are current
operated ones and there are voltage operated ones. Your comments apply
to current devices, mine to voltage devices.
Voltage operated devices are much more reliable for one simple reason,
they dont trip until enough earth current flows to cause a considerable
rise in earth potential. This wipes out the majority of nuisance trips.
Current operated devices are quite a different can of worms, and I dont
have much to say about those.
NT
Andy Wade
> Andy, sorry but I disagree.
That's no surprise - we've been here before...
> I have never seen a voltage operated ELCB which has an earth current
> rating, as you suggest.
ICBW, but I have a fairly clear memory of these being sold as "30mA
earth trips" and similar descriptions in the pre-RCD era. Anyway, after
a bit of a rummage in the TQT pile I found a Crabtree one this
afternoon, shown here with the terminal covers removed:
http://www.zen53070.zen.co.uk/uk_diy/Crabtree_ELCB.jpg
There's no external marking of any trip rating, but the lower terminal
cover carries a moulded legend thus:
For max. earth res of 500 ohm
Impedance of E. L. trip coil 500 ohm
Max tripping current 35 mA
Image here: http://www.zen53070.zen.co.uk/uk_diy/ELCB_legend.jpg
There's no British Standard no., and certainly no indication of any trip
voltage rating/characteristic.
> I have a couple (removed from homes and light commercial premises),
> and have seen many still in use. Of course, since the coil has a
> resistance, ohms law will dictate that there is a tripping current as
> well as a tripping voltage, but that's not how the devices are
> intended to work. They don't expect to see all the current associated
> with any earth leakage in the first place, so a current rating makes
> no sense.
Well that's where we may have to agree to differ.
>>disadvantages were (a) that the coil could easily become shorted (or
>>partially shunted) by parallel earth paths, causing loss of protection,
>
> No, this doesn't cause loss loss of protection (unless the coil
> sense electrode has an overlapping earth resistance area). You
> can have as many parallel earth paths as you like (see diagram
> in 14th edition regs). If you have enough, the ELCB will stop
> working, but this is because it has ceased to be necessary, and
> is not an error situation (it is explicitly allowed for in the
> testing procedure). In this case, and earth leakage will either
> trip the fault current protection or remain safe (CPC not raised
> as much as 50V above real earth).
I can see your argument, for a device working in the way you claim, but
if the ELCB didn't operate then an earth fault would not necessarily be
cleared, since the current will be limited by the earth resistance at
the supply end (distribution transformer earthing) and might not be
sufficient to cause an OPD to operate. The local earth voltage would
not rise sufficiently to cause danger from shock, but there's a risk of
danger from thermal effects and of shock to other consumers on the
network, since the supply neutral will have been pulled well away from
earth.
What test procedure are you referring to above? An earth fault must be
cleared somehow, and in a TT system you can't rely on getting enough
current to operate an OPD, so the ELCB or RCD simply _must_ operate
within the permitted disconnection time.
I don't have a copy of the 14th edition, but ELCBs were still permitted
during the early part of the life of the 15th.
Here are the relevant regs from the 15th ed. (OCR'd). I see nothing to
suggest any requirement of a separate sensing earth electrode:
413-6 Where compliance with the disconnection times of Regulation 413-4
is afforded by a residual current device in an installation which
is part of a TN or TT system, the product of the rated residual
operating current amperes and the earth fault loop impedance in
ohms shall not exceed 50. If a fault-voltage operated device is
used in a TT or IT system the earth fault loop impedance,
including the earth electrode resistance, shall not exceed 500
ohms.
NOTE - For TT systems the earth fault loop impedance includes the
earth electrode resistance.
413-11 Where protection is afforded by fault-voltage operated protective
devices, all exposed conductive parts and associated extraneous
conductive parts protected by any one such protective device
shall be connected by protective conductors to an earth electrode
via the voltage-sensitive element of that device.
413-12 The protective devices shall be of one or more of the following
types:
- residual current devices,
- overcurrent protective devices,
- fault-voltage operated protective devices.
NOTE - Residual current devices are preferred.
471-15 Automatic disconnection using fault voltage operated protective
devices is recognised for use in TT and IT systems and is
suitable where the impedance of the earth fault loop prevents
compliance with Regulations 413-4 and 413-5 by the use of
overcurrent protective devices.
NOTE - The use of residual current devices is preferred.
531-9 The characteristics of every fault-voltage operated protective
device shall be such as to comply with Regulation 413-3 for
automatic disconnection in the event of a fault of negligible
impedance between a phase conductor and exposed conductive
parts, taking into account the impedances of the fault current
loop at every point at which this method of protection is to
be applied. For TT systems, allowances shall be made for any
likely increase in the value of earthing resistance with time,
for example, with seasonal variations (see also Section 544).
544 EARTHING, AND PROTECTIVE CONDUCTORS, FOR FAULT-VOLTAGE OPERATED
PROTECTIVE DEVICES
544-1 Where protection for safety is afforded by a fault-voltage
operated protective device, the requirements of Regulations 544-2
to 544-5 shall be observed.
544-2 An independent earth electrode shall be provided outside the
resistance area of any other parallel earth. If by sub-division
of the earthing system discrimination in operation between a
number of fault-voltage operated protective devices is to be
afforded, the resistance areas of the associated earth electrodes
shall not overlap.
544-3 The voltage-sensitive element of the protective device shall be
connected between the main earthing terminal and the earthing
conductor.
544-4 The earthing conductor shall be insulated to avoid contact with
other protective conductors or any exposed conductive parts or
extraneous conductive parts, so as to prevent the voltage-
sensitive element from being inadvertently bridged.
544-5 Protective conductors shall be connected only to the exposed
conductive parts of those items of equipment whose supply is to
be interrupted in the event of operation of the fault-voltage
operated protective device, and to any extraneous conductive
parts in the same equipotential zone.
613-16 Where protection against indirect contact is to be provided by
a residual current device or a fault voltage operated
protective device, its effectiveness shall be verified by a
test simulating an appropriate fault condition and independent
of any test facility incorporated in the device (see Item 6 of
Appendix 15).
[Testing]
6.2 Operation of fault-voltage operated protective devices
A test voltage not exceeding 50V r.m.s. a.c., obtained from
a double wound transformer connected to the mains supply, is
applied across the neutral and frame terminals and the device
shall trip instantaneously. The transformer has a short-time
rating not less than 750VA (see Figure 19).
Figure 19 (scanned) is here:
http://www.zen53070.zen.co.uk/uk_diy/IEE15_fig19.gif
My sample Crabtree device trips at a shade over 40 mA RMS, at which
current the voltage across the coil is about 11.5 V. The coil impedance
is thus under 300 ohms (its DC resistance is about 160 ohms). When
tripped (or just switched off) the coil is shorted out (by the contact
pair shown under the coil symbol in the legend photo).
At this point I'll rest my case and let you ponder...
--
Andy
Andrew Thelwell
Yes, it may not have been a screwdriver at all, it just looked a bit
like one, and it certainly wasn't a neon bulb in the end... it had
(more than one) small red LEDs fitted into the handle, as I remember...
Don't know if that makes any difference?
Regards,
Andy
Andrew Gabriel
meow...@care2.com writes:
>
> You illustrate the first problem with elcbs, namely that there is more
> than one type of device referred to as an ELCB. There are current
> operated ones and there are voltage operated ones. Your comments apply
> to current devices, mine to voltage devices.
A Current Operated ELCB is the original name for an RCD
(14th Ed wiring regs).
--
Andrew Gabriel
John Rumm
> Yes, it may not have been a screwdriver at all, it just looked a bit
> like one, and it certainly wasn't a neon bulb in the end... it had
> (more than one) small red LEDs fitted into the handle, as I remember...
Something like
http://www.voltstick.co.uk/product.htm
> Don't know if that makes any difference?
Well, they are safer to use in the sense they are non contact - no need
to go exposing live parts just to touch them. You can still get silly
results with them though.
Dave Plowman (News)
Andrew Thelwell <andy.t...@gmail.com> wrote:
> Yes, it may not have been a screwdriver at all, it just looked a bit
> like one, and it certainly wasn't a neon bulb in the end... it had
> (more than one) small red LEDs fitted into the handle, as I remember...
> Don't know if that makes any difference?
Something like this?
http://www.tlc-direct.co.uk/Main_Index/Test_Meters_Index/Dilog_TM6741/index.html
--
*Warning: Dates in Calendar are closer than they appear.
Andrew Thelwell
No -- it was a 'single stick' unit... like a screwdriver or pen type
appearance. My memory says it looked more like a screwdriver but it
wasn't a screwdriver per se.
Something more like the voltstick, yes...
Regards,
Andy
Andrew Thelwell
Dave Plowman (News)
Andrew Thelwell <andy.t...@gmail.com> wrote:
> No -- it was a 'single stick' unit... like a screwdriver or pen type
> appearance. My memory says it looked more like a screwdriver but it
> wasn't a screwdriver per se.
> Something more like the voltstick, yes...
These are even more unreliable than a neon tester. Ok as a safety aid - if
it lights don't touch it, but no use at all for fault finding.
--
*A conclusion is the place where you got tired of thinking *