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

[JohnD]

Why would anybody go the trouble of inventing and manufacturing a unidirectional device?

 

[SUNRAY]

Why would anybody go the trouble of inventing and manufacturing a unidirectional device?

Have you read that Technical Bulletin?

 

[SUNRAY]

Interestingly from that Technical Bulletin:

BS 7671 requires persons to employ good workmanship and to use proper materials, as
a fundamental principle in Regulation 134.1.1. Additionally, the installation of electrical
equipment must take account of the manufacturer’s instructions as stated in both Regulation
134.1.1 and Regulation 510.3. Contravening these requirements could be deemed to be non-
compliant with BS 7671 and not following manufacturer’s instructions will invalidate any
device certification and warranty.

 

[JohnW2]

I looked at @flameport example and

is shown on the bidirectional literature.

... which, as you observe, is not only the opposite of what the Wiring Matters article says, but also makes absolutely no sense (whereas the Wiring Matters text does), since if a device has "Load" written at one end (and presumably something like "Supply" at the other end), it surely is intended to be regarded as ("uni") directional', isn't it?

 

[JohnW2]

Why would anybody go the trouble of inventing and manufacturing a unidirectional device?

Quite so - particularly given that, as have been discussed, to design such a device (with no obvious purpose/advantage I can think of) would seeming be very difficult (hence probably also expensive)

 

[JohnD]

Have you read that Technical Bulletin?

No.

 

[JohnW2]

Interestingly from that Technical Bulletin: ....
BS 7671 requires persons to employ good workmanship and to use proper materials, as a fundamental principle in Regulation 134.1.1. Additionally, the installation of electrical equipment must take account of the manufacturer’s instructions as stated in both Regulation 134.1.1 and Regulation 510.3. Contravening these requirements could be deemed to be non-compliant with BS 7671 and not following manufacturer’s instructions will invalidate any device certification and warranty.

Interesting", perhaps, but of no relevance in relation to bi-directional and uni-directional RCDs, regs 134.1.1 and 510.3 probably being two of the most vague/general regs in the whole book.

... and, of course, as often discussed, even 510.3 now only requires (as correctly stated in your extract above) one to "take MIs into account", not necessarily to comply with them.

 

[JohnW2]

As those who have read the Wiring Matters article will know, it says:

These compact RCBOs contain electronic components and are typically unidirectional. Arc fault detection devices (AFDDs) are also typically unidirectional.

In trying to make some sense of that statement (if it is correct), the only thing I can think of is that the devices they refer to can only be reset 'electronically (or, at least, cn only be reset when the electronics are powered. If that were the case then, if they were installed such that the electronics were being powered from the 'load' side of the device, it would be impossible to reset them, so that would be a good the reason they could only be installed 'one way around' - but the obvious way of removing that problem would be for there to be provision for purely 'mechanical' re-setting (which, I must admit, I always thought was the case).

As JohnD has also said, I still find it almost impossible to believe that anyone would go to the (probably considerable) trouble of developing and manufacturing a device that could only detect, and react to, residual currents when the device was installed 'one way around' - functionality for which I personally cannot see any conceivable useful purpose. I therefore also find it 'almost impossible to believe' that any devices described as "unidirectional" actually do have such functionality.

Kind Regards, John

 

[SUNRAY]

No.

That seems very short sighted bearing in mind it does indicate the reason this whole thread can exist.

 

[TimboTwo]

https://www.cef.co.uk/guides/emergency-3rd-amendment-to-bs-7671-wiring-regulations?utm_source=marketo&utm_medium=email&utm_campaign=UK-EB-2024-05-IET-Regs-Amendment&mkt_tok=MDUwLUZKUy05NzMAAAGS-HTMUhW212vIWBx40XBV2XRYOIz_BEUtBKQ4jGIebzx8wEDq_xiAo07HyIe-I0jO_7qyvZ_6gvXCIu5MdGylBnvXbEIhoMNDWi_ouKbPQU4

 

[JohnW2]

View attachment 342633

It is obviously desirable that, when current may flow 'either way' (as in solar installations etc.) that RCDs are capable of detecting and dealing with residual currents in both directions.

The authors of the 'Emergency Amendment' obviously believe that there are RCDs (maybe just RCBOs) out there which cannot cope with residual currents in both directions - but, as I and others have said, I can't see why such devices should exist - even thoough there is perhaps something wrong with my thinking!

As I recently wrote, I can see how it might be possible that there might be devices that can only 'work' (at all) if connected one way around (and hence would bear 'directionality' markings - which some are saying means that the device is 'uni-directional', but they would obviously not be installed the wrong way around. However, I still find it hard to believe that anyone would have made a device which can detect residual current flowing in one direction., but not the other direction.

There presumably are things which I don't know or understand.

 

[EFLImpudence]

I am not sure I understand all this.

Leaving aside the fact that it is 'alternating current' so presumably going both ways everywhere anyway.


Through the RCD, the Line current and Neutral current (while alternating) go in different directions. If this were not the case the RCD would not and could not work as there would be no residual current.

So how does the RCD know which way the current is travelling as it only detects - or more correctly reacts to - the difference (residual) between the two.


Also, would the RCD notice if the Line and Neutral conductors were swapped? This must reverse the direction in the RCD.

And - as per post #23, why don't Hager even know what bidirectional means?

 

[ericmark]

As far as I can tell, two issues, one inside the MCB

we have 8 Arc divider/extinguisher which is often only on one side, and second is the test button

8 which often is disconnected as the device trips, so all the sense circuitry 7 is isolated as the device trips, sending power in the reverse direction can result in the circuitry remaining powered.

So can see why direction is important, however what seems to be the problem is identifying which items are bi and which are omni directional. It is all well and good referring to load markings, but the links given by @flameport show even with duel direction we still see load marked on the device.

It could well be they have used stock pictures, however they may also use stock casings, for the installer easy, if it does say feed or load one rejects them, however not so easy for some one doing an EICR, if you see load on the casing and fail the installation as a result, and it seems this will be a code C2, and then the installer comes back and says you got it wrong, see this part number is listed and duel direction who is going to pay?

If I find load marked on my MCB's and I call the installer and say you have fitted the wrong type, and they visit and find not wrong type who will pay for their visit. There are two MCB's in my install and I do not have a clue if they comply.

 

[JohnW2]

I am not sure I understand all this.

If you did understand, you might well be the only one who did

Leaving aside the fact that it is 'alternating current' so presumably going both ways everywhere anyway. .... Through the RCD, the Line current and Neutral current (while alternating) go in different directions. If this were not the case the RCD would not and could not work as there would be no residual current.... So how does the RCD know which way the current is travelling as it only detects - or more correctly reacts to - the difference (residual) between the two.

I think it can be done with AC but, as bernard suggested, would probably be very complicated, and it would not seem to make any sense to expend considerable effort to create something which, as far as I can see (unless I'm missing something, would serve no useful purpose. I know that, at least a high frequencies 'it can be done with AC' because, in my youth, I used "Standing Wave Ratio" meters, which were able to distinguish between signals travelling to an antenna (then called 'aerial' ) via it's feeder cable and reflected signals which were 'coming back in the same cable. I confess that I never really understood how they achieved that!

Also, would the RCD notice if the Line and Neutral conductors were swapped?

One wouldn't think so.

This must reverse the direction in the RCD.

I'm not so sure about that, so would need to think more carefully

And - as per post #23, why don't Hager even know what bidirectional means?

Seemingly not (assuming that Hager actually wrote that), as I observed in post #26 - which would seem pretty extraordinary.

Kind Regards, John

 

[DetlefSchmitz]

People seem to be talking about current direction flow, which is clearly meaningless in this context. It is the direction of power flow that is being addressed by the amendment.
It would seem that where an RCD is designed as uni-directional, on tripping, if the device is connected back to front there will be some circuitry and or solenoid that should be disconnected by the operation of the device, but that remains connected, and fries.