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Old July 15th, 2005, 03:08 AM   #1
REZAR
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Red face how elcb works?

Dear all, how are you? fine i hope.
i wish to have explanation on how elcb works.
i know a little about how it trip with unbalance output and input voltage, or it isn't so? but i need what kind of sensor it used?

thanks in advance,
reza
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Old July 15th, 2005, 06:36 AM   #2
Nigel Betteridge
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Live and neutral lines are fed through a sensing transformer. All the while the outgoing current matches the returning current, the transformer is balanced. However, if a leakage path to earth develops downstream of the elcb (they are called RCD's in the UK these days), the returning current will now be less than the outgoing current and and the sensing transformer will be unbalanced, which in turn will trip the device isolating the output from the input.

One common misconception with RCD's is that they need an earth connection to work. They don't

Regards,
Nigel
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Old July 17th, 2005, 10:39 PM   #3
REZAR
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Thanks Nigel,
the sensor is kind of transformer, neutral and live line is balanced.
also in 3phase ? there is in, but i cant figure where is the out.....?
help me please...
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Old July 18th, 2005, 08:10 AM   #4
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Quote:
Originally Posted by Nigel Betteridge
Live and neutral lines are fed through a sensing transformer. All the while the outgoing current matches the returning current, the transformer is balanced. However, if a leakage path to earth develops downstream of the elcb (they are called RCD's in the UK these days), the returning current will now be less than the outgoing current and and the sensing transformer will be unbalanced, which in turn will trip the device isolating the output from the input.

One common misconception with RCD's is that they need an earth connection to work. They don't

Regards,
Nigel
Nigel
I would like to know what the acronyms RCD and ELCB stand for.
These sound like Ground Fault Condition Interrupters (term used here in USA).
Is that what these are?

Thanks

Dan Bentler
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Old July 18th, 2005, 08:21 AM   #5
Paulus
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ELCB = Earth Leakage Circuit Breaker
RCD = Residual Current Device

Regards
Paulus
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Old July 18th, 2005, 08:32 AM   #6
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Quote:
Originally Posted by REZAR
Thanks Nigel,
the sensor is kind of transformer, neutral and live line is balanced.
also in 3phase ? there is in, but i cant figure where is the out.....?
help me please...
Rezar
not sure what you mean by the out?
If you mean how does it trip then the it is usually a mechanical device
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Old July 18th, 2005, 08:46 AM   #7
rsdoran
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Dan they are also called Ground Fault Interrupts (GFI). They basically measure the current thru both wires, since this current is flowing in opposite directions it will negate. If the device senses current that triggers an interrupt.

Its not necessary to use a ground but a ground connection may eliminate more possibilities of a shock hazard.
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Last edited by rsdoran; July 18th, 2005 at 08:50 AM.
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Old July 18th, 2005, 09:00 AM   #8
leitmotif
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Paulus Thanks for definitions
Ron Forgot GFI (although GFI is in GFCI so I guess I am lucky there)

Looked into this several years ago when I was working in safety. No one really knew how they really worked so I contacted Square D who sent me a schematic of the internals.

Essentially what they do is send the "goes in" wire (you can call it hot) and "goes out" (you can call it neutral or identified) wire thru a torroid transformer (basically a current transformer) As long as the current in both conductors is identical the transfromer secondary has no current. If there is a difference in current between "goes in" and "goes out" then there is current in the transformer secondary which is sent to the trip circuit tripping the switch.

SO they do not detect current to ground.
They DO sense a mismatch in the line
AND it is assumed the imbalance current is going to ground.

This is why you can use them in ungrounded wiring
- although a correct statement let me repharase that for most common applications
"you can use them where the circuit has no
GROUNDING (green in USA) conductor
(not the GROUNDED or neutral or identified -- white or gray in USA).

Dan Bentler
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Old July 18th, 2005, 12:45 PM   #9
Nigel Betteridge
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Dan,

Sorry I left the definitions for ELCB and RCD out in my first post, and thanks to Paulus for doing so. In future I will try to pause longer before hitting "submit reply" button.

Rezar,

I'm not sure what you mean by your second post either, so the following may not help. How many connection terminals has your ELCB got? If four, then it is almost certainly a single phase device, and if eight, it is almost certainly a three phase device.

Regards,
Nigel
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Old July 20th, 2005, 04:40 AM   #10
REZAR
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Talking

sorry to make you confuse guys, guess i must study more english.
i had it all now. thanks and toast for you Dan,
Nigel,Paulus, Stevebot, Rsdoran, thanks to all.

but one question more,

is it save enough if i try to shock my self after i push TEST button?

iam happy to make other people think that iam crazy... ....

(besides, it will QC pass by me... isnt it?..)
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Old July 20th, 2005, 06:18 AM   #11
Nigel Betteridge
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I can't imagine anyone who frequents this forum suggesting you test one of these devices by giving yourself a shock. I am NOT an expert in these matters, but I believe 30mA (on the assumption that your ELCB trips at 30mA) can still kill people if they have a heart condition. Even if you havn't, you would still get a shock. NOT to be recommended.

Regards,
Nigel
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Old July 20th, 2005, 06:28 AM   #12
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Rezar
When I was an apprentice one of the things the electricians used to do was test the earth leakage devices. On the odd quiet moment in the workshop just for a "laugh" they would test the device by holding a screwdriver on a live terminal and flicking the bare blade with their finger to make the device trip. The earth leakage trip is fast (30ms) but you still felt a tingle.
Unfortunately once one did not trip. Luckily no one hurt but it demonstrated that man can be foolhardy.
The test button is a good test but their are devices out their to plug i and do the same job. Fingers are not one of them. As Nigel so rightly says
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NOT to be recommended.
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Old July 20th, 2005, 08:07 AM   #13
leitmotif
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NEVER NEVER use yourself as a test instrument. War story at end.
Here in USA GFCI is supposed to trip at 6 mA. Supposedly any voltage greater than 30 and or current greater than 10 mA can be lethal.

Friend of family was elevator electician. Had very dry skin and fairly calloused. Could stick finger in light socket and feel tingle. 240 was OKfor him also. He was only person I ever saw who could do this. Had other friend of family who saw this and asked if he could try - Vince said sure. After Dunc picked himself off floor he was pretty mad and asked Vince why he let him do it. Vince said well you never asked if you would get shocked.

Dan Bentler
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Old July 20th, 2005, 08:28 AM   #14
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Good analogy for ELCB/RCD , use a CT coil on the incomer to the panel (3 phase , put it over all three phases - it should read nothing ) if you have a leakage to earth , the the CT transformer will read the loss , it is a load not being absorbed across the three phases , the electronics detects that and trips .(before anyone tells me , I know that an isolating tranny will fool the analogy)
Don't expect a device sold for $20 to be that accurate , 30mA may be more or less , though these cheap devices are surprisingly accurate , if you want to test one , use a dedicated reaction time tester.
Don't test it with your finger - use someone elses . All joking aside - Jangan main-main sama listrik , Mas - Ojolali , ya ?
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