Residual current measurement

[who where]

On Mon, 06 Sep 2010 19:42:27 +1000, John G <greentest@ozemail.com.au>
wrote:

You do not understand Earth Leakage.

There is no need for an EARTH conductor

other than regulatory/safety concerns

and measuring just THAT current is not a solution.

correct

Earth Leakage or actually Imbalance of current between the active and
the neautral can follow many paths.

correct

Hence to measure it you need a pair of CTs and a very good resolution
method of reading the difference between the 2.

Wrong. A single core balance device - i.e. a CT - will provide the
difference signal,and more so than trying to resort to measuring the
difference between two CT's.

Simple solution is a portable RCD which is carefully designed to do
JUST this job.

or a proper RCBO

 

[John G]

On Mon, 06 Sep 2010 19:42:27 +1000, John G <greentest@ozemail.com.au
wrote:

You do not understand Earth Leakage.

There is no need for an EARTH conductor

other than regulatory/safety concerns

Regulatory requirements are not REALLY a part of solving the problem.
Sure some situations are required to be EARTHED but that has nothing to
do with the operation of an RCD.
If there is an earth connection then it is part of the execise but it
is not necessary for an RCD to operate.

and measuring just THAT current is not a solution.

correct

Earth Leakage or actually Imbalance of current between the active and
the neautral can follow many paths.

correct

Hence to measure it you need a pair of CTs and a very good resolution
method of reading the difference between the 2.

Wrong. A single core balance device - i.e. a CT - will provide the
difference signal,and more so than trying to resort to measuring the
difference between two CT's.

Well yes a proper differential CT would do the job, but of course that
is what an RCD does however it is constructed.
But a traditional CT is just used to measure A current in A wire.

Simple solution is a portable RCD which is carefully designed to do
JUST this job.

or a proper RCBO

What is an rcBO?? Google does not yield much info.

--
JohnG

 

[Grant]

On Tue, 07 Sep 2010 19:41:07 +1000, John G <greentest@ozemail.com.au> wrote:

On Mon, 06 Sep 2010 19:42:27 +1000, John G <greentest@ozemail.com.au
wrote:

You do not understand Earth Leakage.

There is no need for an EARTH conductor

other than regulatory/safety concerns

Regulatory requirements are not REALLY a part of solving the problem.
Sure some situations are required to be EARTHED but that has nothing to
do with the operation of an RCD.
If there is an earth connection then it is part of the execise but it
is not necessary for an RCD to operate.

and measuring just THAT current is not a solution.

correct

Earth Leakage or actually Imbalance of current between the active and
the neautral can follow many paths.

correct

Hence to measure it you need a pair of CTs and a very good resolution
method of reading the difference between the 2.

Wrong. A single core balance device - i.e. a CT - will provide the
difference signal,and more so than trying to resort to measuring the
difference between two CT's.

Well yes a proper differential CT would do the job, but of course that
is what an RCD does however it is constructed.
But a traditional CT is just used to measure A current in A wire.

Simple solution is a portable RCD which is carefully designed to do
JUST this job.

or a proper RCBO

What is an rcBO?? Google does not yield much info.

over current breaker built in, I found that in 20 seconds

Grant.

 

[Phil Allison]

"John Goose"

You do not understand Earth Leakage.

There is no need for an EARTH conductor and measuring just THAT current is
not a solution.

** For the vast majority of *appliances* that plug in to an AC outlet -
this claim is utterly FALSE .

Earth leakage can only occur via the ground wire and if there is not one (
ie Class 2 wiring) then earth leakage is not possible until the item is
provided with path to earth - via external wiring or body contact.

Earth Leakage or actually Imbalance of current between the active and the
neautral can follow many paths.

** But all of them are to ground.

Hence to measure it you need a pair of CTs and a very good resolution
method of reading the difference between the 2.

** Insane crap.

One merely measures the current flowing in the ground conductor of an
appliance OR in the case of Class 2 appliances one tests for current flow
between any exposed metal and the supply ground.

The procedure is simple and involves only a AC volt meter and a low value
resistor to provide a suitable voltage drop. The safe limit is in the order
of a milliamp or two depending on the class of appliance.


...... Phil

 

[Metro]

"bristan" <none@none.com> wrote in message
news:4c8333e8$1@dnews.tpgi.com.au...

"Noodnik" <Noodnik@NotHere.com> wrote in message
news:fuCdnSVIb85ocB_RnZ2dnUVZ8n6dnZ2d@westnet.com.au...
Hi, House is going out on residual current occasionally, all the obvious,
easy checks have been done. Has anyone come across a device that
measures residual current of appliances, or built one? A CT is obviously
a good first step, but I wonder whether geometry or interwinding
screening needs to be consdered to achieve the sensitivity required.

Any other practical suggestions to sort this problem, aside from
contacting a qualified, licenced electrician?
A fairly common problem in houses a few years old according to the
electrician who fixed mine.
A clothes drier was tripping out the device when we switched it on.
He fitted a second one to the board and divided up the circuits
accordingly.
No further problems

I take none of you clowns are qualified. Most of your theories are crap .
Remember a little knowledge is dangerous. I am qualified, but would not
impart any of it to any of you. Folk pay me for my skills. Mr Allison seems
to be the most cluey out of all of you.

 

[mark krawczuk]

"Metro" <stand@attention> wrote in message
news:4c8b2616$0$3032$afc38c87@news.optusnet.com.au...

"bristan" <none@none.com> wrote in message
news:4c8333e8$1@dnews.tpgi.com.au...

"Noodnik" <Noodnik@NotHere.com> wrote in message
news:fuCdnSVIb85ocB_RnZ2dnUVZ8n6dnZ2d@westnet.com.au...
Hi, House is going out on residual current occasionally, all the
obvious, easy checks have been done. Has anyone come across a device
that measures residual current of appliances, or built one? A CT is
obviously a good first step, but I wonder whether geometry or
interwinding screening needs to be consdered to achieve the sensitivity
required.

Any other practical suggestions to sort this problem, aside from
contacting a qualified, licenced electrician?
A fairly common problem in houses a few years old according to the
electrician who fixed mine.
A clothes drier was tripping out the device when we switched it on.
He fitted a second one to the board and divided up the circuits
accordingly.
No further problems

I take none of you clowns are qualified. Most of your theories are crap .
Remember a little knowledge is dangerous. I am qualified, but would not
impart any of it to any of you. Folk pay me for my skills. Mr Allison
seems to be the most cluey out of all of you.

mmm i suppose you didnt mind getting knowledge from aother people while

you where learning... then again who wants to know what a 3 year old could
know ??

 

[Clifford Heath]

Noodnik wrote:

Hi, House is going out on residual current occasionally,

I had the RCD go out at 7:58AM precisely, once or twice a week,
for months. It actually happened for a month before I realised
that it was always the same time. Then I started leaving things
that have a clock in them unplugged, since whatever it was, it
clearly knew the time of day... no help.

So I started hassling the electricity supplier, since it was
clearly being caused by something they were doing with the supply.
They claimed the RCD was faulty and should be replaced, even though
it was brand new (the house was completely rewired in a reno).
I insisted that the RCD has no clock in it, therefore could not
know when it was 7:58AM, and could not be at fault.

This went several rounds, before they finally admitted that at
7:58 each morning, they switch some large capacitor banks in to
change the load phase, in anticipation of industry firing up some
large inductive loads. They agreed to send sparkies round to
change the RCD to one that's less sensitive to the disruption.

The sparkies reckoned they had done hundreds, to fix the same
behaviour.

There was no fuss about this in the media, and I'm sure that for
every RCD the power company replaced, there were twenty more
customers who paid the bill themselves. Shonky, or what?

Clifford Heath.

 

[who where]

On Fri, 08 Oct 2010 07:27:05 +1000, Clifford Heath
<no@spam.please.net> wrote:

Noodnik wrote:
Hi, House is going out on residual current occasionally,

I had the RCD go out at 7:58AM precisely, once or twice a week,
for months. It actually happened for a month before I realised
that it was always the same time. Then I started leaving things
that have a clock in them unplugged, since whatever it was, it
clearly knew the time of day... no help.

So I started hassling the electricity supplier, since it was
clearly being caused by something they were doing with the supply.
They claimed the RCD was faulty and should be replaced, even though
it was brand new (the house was completely rewired in a reno).
I insisted that the RCD has no clock in it, therefore could not
know when it was 7:58AM, and could not be at fault.

This went several rounds, before they finally admitted that at
7:58 each morning, they switch some large capacitor banks in to
change the load phase, in anticipation of industry firing up some
large inductive loads. They agreed to send sparkies round to
change the RCD to one that's less sensitive to the disruption.

The sparkies reckoned they had done hundreds, to fix the same
behaviour.

There was no fuss about this in the media, and I'm sure that for
every RCD the power company replaced, there were twenty more
customers who paid the bill themselves. Shonky, or what?

The amplifier in most RCD's is sensitive to HF/RF which may be induced
into the core via the line. We have had many experiences with RCD's
tripping when RF has been superimposed on the line. Invariably
fitting a common mode choke (ferrite toroid) over the line has
addressed this without compromising proper tripping operation.

Whether the same sensitivity to the supply authority's control tones
exisits I can't say, but it *is* a distinct possibility. If they have
a 30mA unit replaced with another 30mA unit and it fixes the problem,
you can bet that the replacement has increased immunity to the control
tones aka some additional line-side filtering.

 

[Clifford Heath]

who where wrote:

Whether the same sensitivity to the supply authority's control tones
exists I can't say, but it *is* a distinct possibility. If they have
a 30mA unit replaced with another 30mA unit and it fixes the problem,
you can bet that the replacement has increased immunity to the control
tones aka some additional line-side filtering.

That would certainly match with what both the supplier and the sparkies
told me, given their somewhat low level of technical understanding.

Nice (for others) to know that a toroid could fix it, but for me, even
nicer that someone else did it for nothing ;-).

Clifford Heath.

 

[terryc]

Noodnik wrote:
Hi, House is going out on residual current occasionally,

Cheap electric jug?
That is what does it for us. the element corrodes and it starts throwing
the RCD. Replace the jug and problem solved.