Residual current measurement

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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?



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Nobrainer in fact. CT on the earth lead of the appliance.



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"Noodle dick"
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** Someone with no brains would do that.



....  Phil



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See guys Phil is alive and well, just noone had posted a stupid and
dangerous enough suggestion to provoke him.

(CT on the phase and neutral wires is the correct answer)

--
¡spuɐɥ ou 'ɐꟽ ʞooꞀ


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I had a problem trying to sort out why a newish switching supply trip
RCD, yet it worked fine in the shop.  So far all I can guess is that it's
due to poor earthing, I'm in rear unit with long earth run, and my friend
hand problems up the back shed, also a long earth run.

More here for the curious: http://grrr.id.au/ps-earth-current /

I could stop the RCD from triggering with some extra inline filtering,
but there's not a lot one can do for conducted interference down the
earth lead?  In the end the PS owner decided not to do anything, unless
it tripped on customer's site (Ouch!) embarrassing.

Grant.

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I had a dedicated ELCB dual GPO fitted to a workbench where radio
equipment is serviced (this is *years* before RCD's became
law/popular).  It used to trip when a transmitter connected to a large
DC PSU was fired up.  Putting a large ferrite toroid over the DC lead
stopped the RF getting back into the ELCB core.  Clipsal confirmed
that their core balance amp was conducted-RF-sensitive.

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Wouldn't surprise me, close to 10mA of 28kHz triggered the thing ;)

But I needed lots more than ferrite over the wire, a few turns of the
three leads through a pair of large toroids, too fugly to contemplate
as an add-on.

Grant.

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other than regulatory/safety concerns

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correct


correct


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.

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or a proper RCBO

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Same difference, almost, except that last 'O' gives overload protection,
a bit better.

Grant.

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

--
JohnG



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

Grant.

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"John Goose"

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** 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.


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** But all of them are to ground.

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** 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




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Noodnik formulated the question :
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The fault current may not flow thru the earth lead.
It may flow from the frame of someting not earthed thru YOU.

Double insulated devices without an earth lead can still trip an RCD if
they are faulty.

--
JohnG



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Would need to measure the current on the active and neutral to the
appliance, at the same time, and calculate the difference if any.
That difference will be your leakage & that is how your ELCB works.


-Buy a "Megger" tester and test each appliance in your premises with
it. This will also help reveal any suspect device that might be
breaking down, but not enough yet to trip an ELCB.

If the ELCB is tripping because of several appliances leaking a
little, and the cumulative leakage current being enough to trip the
ELCB, this is about the only way you are going to find it.


-Buy a portable ELCB, or roll your own by building an ELCB into a
suitable enclosure with a plug and socket on it and plug it in series
with each appliance in turn until you get it tripping.
You might have to build your own anyway if you are want to test or
protect portable devices that are 15A or over, or are 3 phase as
portable consumer ELCB's are typically 10A single phase.
When it trips, than you have found the culprit device.


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out on residual current occasionally, all the obvious,
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Which will promptly destroy many electrical devices.



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I would assume that it is going to be used properly ??



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"kreed"

Would need to measure the current on the active and neutral to the
appliance, at the same time, and calculate the difference if any.
That difference will be your leakage & that is how your ELCB works.


** Totally STUPID crap.



-Buy a "Megger" tester and test each appliance in your premises with
it. This will also help reveal any suspect device that might be
breaking down, but not enough yet to trip an ELCB.

** Totally STUPID crap.



If the ELCB is tripping because of several appliances leaking a
little, and the cumulative leakage current being enough to trip the
ELCB, this is about the only way you are going to find it.

** Totally STUPID crap.








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You can buy an extension lead with RCD built in, try it on appliances you
suspect.

What's new in, on the house, to cause a problem?  

Grant.

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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


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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.



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