Need a portable RCBO to trip faster than general

[Energizer]

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?

 

[DPG]

What do you mean by trip faster? Your other thread has already covered this.

Are you saying 40mS is not fast enough for your application?

 

[Avo Mk8]

I want to have a portable power strip with RCBO that trips faster than general. Is there a way to do that?

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:

https://docs.rs-online.com/c790/0900766b817040ad.pdf

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

 

[Rockingit]

I suspect that what's happening is that the OP is experiencing nuisance upstream RCD trips and wants to try to solve it by having the downstream trip first.

 

[Energizer]

What do you mean by trip faster? Your other thread has already covered this.

Are you saying 40mS is not fast enough for your application?

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.

 

[Energizer]

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:

https://docs.rs-online.com/c790/0900766b817040ad.pdf

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

Interesting idea. Thanks
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?

 

[Energizer]

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)

 

[James]

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.

 

[Energizer]

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.

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.

 

[James]

If you are touching phase and earth together to test this, be aware the current will be in the 100s of amps, not mA

 

[Energizer]

If you are touching phase and earth together to test this, be aware the current will be in the 100s of amps, not mA

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

 

[DPG]

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

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.

 

[Rockingit]

At this point..... "I'm out". The OP is showing a significant lack of knowledge for what they're asking and using a potentially lethal method of testing.

 

[brianmoooore]

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.

 

[Energizer]

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.

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...

 

[Energizer]

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....

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.

 

[DPG]

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.

I really would stop testing like this if I were you. It is not particularly safe, and will stress the RCDs unnecessarily.

 

[Energizer]

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

 

[Energizer]

I really would stop testing like this if I were you. It is not particularly safe, and will stress the RCDs unnecessarily.

Don't worry about that

 

[DPG]

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
View attachment 107374
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.