I have a general RCBO (in attached image) Merlin Gerin multi 9 ID' clic 40A 30mA that protects a house and a second portable RCBO Siemens 10mA that protects a power strip. I tested different RCBO 10mA marked as sensible (some designed for bathroom, high humidity) in this portable power strip - all portable RCBO trip in the same time with general. The simulated fault is residual current leak. I want to have a portable power strip with RCBO that trips faster than general. Is there a way to do that?
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If you take the earth leakage fault, things to consider:
1) The 50Hz ac waveform has a period of 20ms for one cycle. Assuming a simple resistive leakage, and starting with the mains waveform at 0V, it has to rise to a high enough voltage to reach the leakage trip current - if nearing peak voltage that would take 5mS. If the RCBO has been designed to ignore transients, it might want to look at the decending voltage trigger point too, or the -ve half of the cycle as well to do another measurement. If the latter we are talking about at least 15mS, getting on for a full cycle of 20mS. Of course the 'fault' may occur at any point during the cycle, but it's random chance when. Just trying to point out there are physical reasons why you cannot guarantee 'instant'.
2) The 30mA 40mS trip 'standard' has been determined to be safe, so in principle there's no advantage to quicker trip times, unless there is some technical requirement.
3) You could choose a lower trip limit for the leakage current, which by implication would cause a quicker trip. There are fancy earth leakage breakers where you can set trip current, here's an example of one starting at 6mA:
There are no doubt other special purpose safety devices on the market that might do what you want, but understanding what it is you want to achieve by having a faster trip, would help
To trip faster I mean to trigger faster. To pass from the state ON to OFF.
My other thread is only about existence of the fastest RCBO, but this thread is about my security power strip that is intended to trigger first in case of:
Leakage current
Short circuit
Over current
Why I need this? Because I can quickly access the security power strip that is near to me, but the main distribution board let's stay is far away, not easy accessible or even locked and you need a key to open it to enable RCBO again after triggering. And logically, I don't need to build this security power strip if the main RCBO from the main distribution board and security power strip trigger both in the same time.
Interesting idea. ThanksIf you take the earth leakage fault, things to consider:
1) The 50Hz ac waveform has a period of 20ms for one cycle. Assuming a simple resistive leakage, and starting with the mains waveform at 0V, it has to rise to a high enough voltage to reach the leakage trip current - if nearing peak voltage that would take 5mS. If the RCBO has been designed to ignore transients, it might want to look at the decending voltage trigger point too, or the -ve half of the cycle as well to do another measurement. If the latter we are talking about at least 15mS, getting on for a full cycle of 20mS. Of course the 'fault' may occur at any point during the cycle, but it's random chance when. Just trying to point out there are physical reasons why you cannot guarantee 'instant'.
2) The 30mA 40mS trip 'standard' has been determined to be safe, so in principle there's no advantage to quicker trip times, unless there is some technical requirement.
3) You could choose a lower trip limit for the leakage current, which by implication would cause a quicker trip. There are fancy earth leakage breakers where you can set trip current, here's an example of one starting at 6mA:
There are no doubt other special purpose safety devices on the market that might do what you want, but understanding what it is you want to achieve by having a faster trip, would help
I think, in the main distribution board there is an RCBO 30mA. My power strip with integrated RCBO is 10mA. Now I simulate a fault, leakage to the earth. An RCBO is measuring leakage current, right? 10mA current is less than 30mA, right? Then why the 10mA RCBO don't cut off first?
Now about the cycle. It's right that the fault may occur randomly, in the zero position, ascending, descending, positive or negative peak. We know that the speed of electrical current is near to the speed of light, practically instantaneous. If in this moment in the main power board RCBO is positive peak, then on the power strip RCBO is the same positive peak because of instantaneous speed of the current, right?
What I want to achieve is to have a device, a power strip with integrated RCBO that trigger first not affecting the main. Now I started discussion about leakage current, but ideally this power strip should cut the circuit in case of short or overload. Why fast trip? Because I can easily enable my portable RCBO that went off protecting the circuit and not searching the key to open the main distribution board, to not keep all the house or the building without electricity seeking the main RCBO to re activate it after triggering. The main should remain always on when I'm using the portable security power strip. Is this possible?
Here is my security power strip that should cut off only this power strip and not all the house (in case of leakage current. I will see later for short circuit and maybe for over load)
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What you are trying to do is not possible with any degree of reliability
the problem is, when you have an imbalance of current on one device, you will have the same imbalance on the upstream device.
when this happens, the detection circuit of the device will start the trip mechanism to move, most of the 30mS is not the device waiting to see if the imbalance remains for a while, it is the mechanical action of the contacts opening.
the problem is, when you have an imbalance of current on one device, you will have the same imbalance on the upstream device.
when this happens, the detection circuit of the device will start the trip mechanism to move, most of the 30mS is not the device waiting to see if the imbalance remains for a while, it is the mechanical action of the contacts opening.
Yes, I understand the idea about unbalance on the cascading devices. But the sensitivity is not the same. The main should trigger when the leakage current reach 30mA, the second - 10mA. If the both devices trigger in the same time ( maybe not exactly in the same time, but I see both off), then logically the second 10mA device is not enough fast to cut off the circuit before trigger the main device, or there is a nuisance in the line when I touch the phase and earth wire that cause a peak in the line. I will mount a filter to test.
Why 100s? The current is in amps, but RCD trips in 30-40ms and disconnect the circuit. This can happen in real life when you plug in a device with insulation fault, the phase is touching the ground of faulty device
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Think about the instantaneous current that flows when there is a direct phase to earth short circuit. It may only be for a few mS, but it is a large figure.
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If you arrange for the fault current to start at zero and slowly build up, then you will get the discrimination you desire, but this is not what you are doing.
You are applying a fault current of at least many tens of amps which will be reach its peak in a maximum of 5mS, which will trigger both RCDs. That's what they're designed to do and that's what they do.
You are applying a fault current of at least many tens of amps which will be reach its peak in a maximum of 5mS, which will trigger both RCDs. That's what they're designed to do and that's what they do.
I wrote before about the important current that flows to the ground for a few ms. And I explained that this is only a test. But this happened in real life before when a user plugged in a faulty device with direct leak to the earth. The users don't think when they plugs in a faulty device. From another point of view, I want to secure the users outlet without modifying the electrical circuit by adding a dedicated RCD in the main distribution board. Well, we will see what we can do...
And not that the users are doing when they just plug in a faulty device that leaks to ground. I'm simulating this (in the name of the science) and trying to find a solution.
I agree that the both RCD do what they are designed to do.
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I really would stop testing like this if I were you. It is not particularly safe, and will stress the RCDs unnecessarily.
Nobody here mentioned the term of ''selective tripping'', when you have 2 RCD in cascade. In my case, I should replace my general RCD by S type one. The selective residual current protective devices have the identification code S. S=selective. And second RCD should be instantaneous design or short time delayed design, type K
Those who are lacking the knowledge are scratching the head and leaving out
Those who are lacking the knowledge are scratching the head and leaving out
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Nobody here mentioned the term of ''selective tripping'', when you have 2 RCD in cascade. In my case, I should replace my general RCD by S type one. The selective residual current protective devices have the identification code S. S=selective. And second RCD should be instantaneous design or short time delayed design, type K
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Those who are lacking the knowledge are scratching the head and leaving out
We are well aware of those, but you were specifically asking for quicker RCDs!!
Doh, I'm out.
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Members on here are offering you sound advice especially in regard to your 'testing' methods. Any more insults to forum members this thread will be gone.
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If you do decide to go to a type S device you may well be compromising safety. The 40mS is there for a good reason.
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I mentioned this in post #19 of your other thread.Nobody here mentioned the term of ''selective tripping'', when you have 2 RCD in cascade. In my case, I should replace my general RCD by S type one. The selective residual current protective devices have the identification code S.
Those who are lacking the knowledge are scratching the head and leaving out
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Can you enlighten us to the problem and solution ?.
Exactly. Thank you. Only the S type escaped from my attention. I didn't know before about existence of this type of devices. When I've found the selective tripping explanation, this caught instantly my attention
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The problem is that two cascading RCD are tripping in the same time when leak occurs. Because the upstream RCD is not selective.
The potential solution (valid for my laboratory only, let's say) is mentioned in the post #18
I remember to users to not repeat my test if they don't know what they are doing
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You're obviously finding out new things but if you didn't even know that S type devices existed, it just about sums up the knowledge involved in your ideas.
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The testing method you are using is inappropriate. You will damage both RCDs and your installation will with lose power because the upstream rcd no longer turns on, or it will become welded shut, and not trip on fault. Making it unsafe.
The 10 or 30mA is the fault current. If you could simulate an 11, 12, 13 mA fault, then you will find the 10 trips and the 30 doesn’t.
Testing live to earth is creating a massive current.
Voltage divided by resistance = amps.
So 230, or 110 or whatever you use divided by near enough zero is going to give very high current, albeit for a very short time.
In fact, this won’t just be stressing the rcd’s but also any cable, socket pins, circuit breakers that the current has to pass through.
There has been explanations already from professional electricians and the general consensus is that it cannot be done.
Your only solution is to separate the circuit you want from the upstream rcd, either giving it its own rcd, reducing the overall total “resting” earth leakage on each or if permissible, running an non RCD protected circuit to where it needs to be and fitting the rcd there.
The 10 or 30mA is the fault current. If you could simulate an 11, 12, 13 mA fault, then you will find the 10 trips and the 30 doesn’t.
Testing live to earth is creating a massive current.
Voltage divided by resistance = amps.
So 230, or 110 or whatever you use divided by near enough zero is going to give very high current, albeit for a very short time.
In fact, this won’t just be stressing the rcd’s but also any cable, socket pins, circuit breakers that the current has to pass through.
There has been explanations already from professional electricians and the general consensus is that it cannot be done.
Your only solution is to separate the circuit you want from the upstream rcd, either giving it its own rcd, reducing the overall total “resting” earth leakage on each or if permissible, running an non RCD protected circuit to where it needs to be and fitting the rcd there.
I assume the risk and I'll buy new RCD in case of damage. No problem
I wrote before many times - when you plug in a shorted to the ground device, there is no resistance, there are amps leaking for some ms - no stress for the wires and the RCD is doing their job. Manufacturers did the same thing thousands of times in the lab for measurements and to check when the device will fail.
The RCD is designed to protect people. A human body have different resistance depending on different factors, humidity, etc, but the faulty device don't have resistance. The current is searching the shortest way, allways.
In real life this type of fault is happening very rarely when we don't have a multimeter to test the device before plug in, so no stress for RCD or wires, it will not trip every day. I allways push the test button before and after my experiments to verify if the device is still operational.
Well, sorry for my curiosity and motivation to find a solution. For me, "it cannot be done" is the last thing, when I don't have any ideas and there really are no more solutions, proved by real tests or, not economically viable
I added this solution to the list of potential solutions, the same thing with selective tripping solution that requires changing the RCD type, or intelligent RCD, resetting itself safely after a nuisance trip. These solutions are valid but not everywhere.
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Today I performed some tests and I obtained what I want without modifying anything in the house. I modified only my portable RCD power strip. When I plug into my security power strip a faulty device (residual current fault) - then my power strip goes off instantaneously and isolate the faulty circuit from the rest of the house, but the main RCD 30mA it's still on! The portable RCD 10mA trips faster than general. Repeated many times - works like a charm. That's what I wanted 
Next step is to integrate all in one multi protection RCBO - leakage, short, overload protection, or, add short circuit (phase-neutral) protection to existing circuit. Ultra fast fuse, resetable fuse ... how to deal with shorts ?
Next step is to integrate all in one multi protection RCBO - leakage, short, overload protection, or, add short circuit (phase-neutral) protection to existing circuit. Ultra fast fuse, resetable fuse ... how to deal with shorts ?
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What modifications have you made ? Or are you keeping it secret for now due to applying for patent etc.Today I performed some tests and I obtained what I want without modifying anything in the house. I modified only my portable RCD power strip. When I plug into my security power strip a faulty device (residual current fault) - then my power strip goes off instantaneously and isolate the faulty circuit from the rest of the house, but the main RCD 30mA it's still on! The portable RCD 10mA trips faster than general. Repeated many times - works like a charm. That's what I wanted
Next step is to integrate all in one multi protection RCBO - leakage, short, overload protection, or, add short circuit (phase-neutral) protection to existing circuit. Ultra fast fuse, resetable fuse ... how to deal with shorts ?
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Knackered the main rcd I think.
Otherwise, you’ve managed to invent a device that will discriminate between two 40ms RCDs in line.
I’m sure the manufacturers would be interested in investing, because up til now, after 40 years or so, no one has come up with a solution.
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Yes and it also has zero resistance, we are now destined to carry high currents with cables the size of a hair.
Wrong. I tested the main RCD - it works
Wow, you have the ability to measure the resistance and size of cables at distance?
Well, if a little knowledge is dangerous thing, I will not share my solution (to keep the people in safety). They should use what they find on the market and what the certified electricians are saying and never try testing like me, because it's dangerous
For me it works (without breaking any safety rules) and I'm happy
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Wrong. I tested the main RCD - it works
Wow, you have the ability to measure the resistance and size of cables at distance?
Well, if a little knowledge is dangerous thing, I will not share my solution (to keep the people in safety). They should use what they find on the market and what the certified electricians are saying and never try testing like me, because it's dangerous
For me it works (without breaking any safety rules) and I'm happy
Great stuff, glad all worked out OK. Engineering excellence.
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So what were the figures for the main RCD that you claim to have tested?
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He pressed the test button.
It has a test button. The RCD works normally. No melted/welded contacts
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Little bit more to testing a RCD than pushing the button!
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It seems that your laboratory where you do all the experiments and testing for people's safety seems to consist of a piece of wire and your finger.
Not today
You are thinking wrong, or it's just a sarcasm and banter.
Don't worry about my safety. This security device I will use for months, only me. Nobody will be hurted, I promise
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