Bi and Omni directional RCD's how can one tell what has been fitted.

[scousespark]

The unidirectional device has the word 'out'. There are no markings on a bidirectional device.

 

[JohnW2]

Thanks for your input ...

BEAMA published a tech update last year and there was an article in wiring matters 99. The term is unidirectional, not omni.

So I came to realise following flamport's post. !

..... Hi-directional means the device works in both directions so is suitable for prosumer units.

Thanks, but what does "works in both directions" mean in this context?

A 'standard' one (the ones which we "know, love and use") will surely work with the current through L & N going in either direction, otherwise it would be critical which way around that had to be connected - but I thought we were agreed that such does not matter, provided only that (as seems to be standard these days) the test circuit is disconnected by operation of the trip mechanism (to prevent over-heating/destitution of the test resistor if the device is wired one way around and test button is held depressed).

Unidirectional devices have an indicator to show the direction from supply to load, such as an arrow.

I'm getting very confused. Are you perhaps saying that all the RCDs which we 'know, love and use' are, in fact bi-directional, and that it is unilateral ones, if they exist, that are rare (and, as bernard has suggested, would probably be quite complex to produce) ?

Is it not because the RCDs "which we know, love and use" do not have any arrow or in/out markings that we quite often get asked whether it matters which way around they are connected - and that we normally say that it does not matter (give or take the caveat above)? Looking at the ones I have here that I can inspect, I see no 'directionality' indication on any of them.

 

[ericmark]

The unidirectional device has the word 'out'. There are no markings on a bidirectional device.

I looked at @flameport example and

is shown on the bidirectional. It is all well and good buying new, but when doing an EICR how does one know if the units fitted are OK.

I can see the problem however it also says MCB's and I had never considered a MCB could have a problem.

 

[SUNRAY]

I looked at @flameport example and View attachment 342535is shown on the bidirectional. It is all well and good buying new, but when doing an EICR how does one know if the units fitted are OK.

I can see the problem however it also says MCB's and I had never considered a MCB could have a problem.

Well in a nut shell devices cant know which direction the current is flowing as it changes 50 times a second.

 

[JohnW2]

Well in a nut shell devices cant know which direction the current is flowing as it changes 50 times a second.

Do you mean 100 times per second ?

 

[bernardgreen]

Well in a nut shell devices cant know which direction the current is flowing as it changes 50 times a second.

A device could use separate current transformers ( one on Live and one on Neutral ) and a voltage comparator to determine the difference if any between the Live and Neutral currents. Most MCBs use a single current transformer with Live and Neutral in antiphase through the core

The device could then use the phase angle of the voltage on the incoming mains as a timing signal for when to sample and evaluate the currents on the Live and the Neutral through the device. The direction of Live current flow at the timing signal will indicate which direction power is flowing through the device.

 

[JohnD]

My solar inverter is connected to an "ordinary" RCBO in the CU. Same as all the others because I got plenty. Current can flow in either direction.

It's a Memshield 2 type. Around 20 years old now. IIRC it is suitable for AC and rippling DC.

Should I care?

 

[EFLImpudence]

From the first of Flameport's links.

So - either another totally inappropriate name for an electrical item or possible an inaccurate translation from the original.

 

[ebee]

well its got me flummoxed too.

just a thought - I wonder if someone on this forum could ask the esteemed JW to do one of his excellent youtube articles for us mere mortals

 

[davelx]

Reads as a normal RCBO to me "earth leakage and overcurrent"

 

[JohnW2]

From the first of Flameport's links.

View attachment 342556

So - either another totally inappropriate name for an electrical item or possible an inaccurate translation from the original.

... so, are they suggesting that "bi-directional RCD" means "RCBO" -, 'because' it provides over-current as well as residual current protection ?

This is getting a bit ridiculous I still have not got clue as to how a 'bi-directional RCD' would/does differe froim the RCDs which "we know, love and use", and I certainly struggle to think of why anyone would want a 'unidirectional' one (if such exist).

 

[JohnW2]

well its got me flummoxed too. ... just a thought - I wonder if someone on this forum could ask the esteemed JW to do one of his excellent youtube articles for us mere mortals

That would be great, if he could do it - but that would require that he understands what a "bi-directional RCD' actually is (assuming it's different from the RCDs we know) - which may or may not be the case

 

[scousespark]

this may help.

https://www.google.com/url?q=https://www.beama.org.uk/static/c3939aab-9b55-44e0-8b379d55d5fa305b/BEAMA-Technical-Bulletin-Connection-of-Unidirectional-and-Bidirectional-Protective-Devices.pdf&sa=U&ved=2ahUKEwi32Or_wP6FAxXyWEEAHdG8DSgQFnoECAcQAg&usg=AOvVaw2QmmYGgfZ0fERVo_VnlsBx

As may this

Wiring Matters Issue 99 - March 2024

electrical.theiet.org

 

[JohnW2]

this may help.

Thanks. That seems to be saying that an RCD can be assumed to be bi-directional unless they have in/out markings, arrows or whatever to indicate the intended 'direction' of installation. None of the RCDs (RCCBs) I have here bear any such markings and, as I wrote, we frequently see people being advised that RCCBs can 'be installed either way around'.

The implication is that the presence of such markings (for any devices that have them) should be taken to indicate that they are "unidirectional". However, the inclusion of such markers is obviously down (for whatever reason) to the manufacture and I still find it very hard to believe that any such device would fail to detect (and react) to a residual current in 'either direction' - not the least because it would seem to be pretty difficult to engineer a device that would operate in that fashion.

As may this

This Wiring Matters article seems to confirm that most (maybe all?) RCCBs are bi-directional, but suggests that at least some RCBOs and AFDs may not be - but, again, I find it hard to understand how the latter can fail to respond to residual currents in either direction.

If we can't find any better explanations, we might need to interrogate some of the manufacturers, particular those selling devices which have directionality markings, hence allegedly 'unilateral'.

Kind Regards, John

 

[ericmark]

I looked at @flameport example and

is shown on the bidirectional literature. Then read @scousespark link which says

A protective device that does not have markings to indicate line and load terminals is a bidirectional device

So it seems we are back to square one, we know what the problem is when connecting to power supplies through a unidirectional in that parts can remain energised after the device has tripped, however I still have no idea how to look at a device already installed and see if it is bi or unidirectional.