Hi Andy

There are several things it tries to address.

Power on the load side of a circuit could burn out the circuitry of lets say an RCBO as it in effect has an inwards side and an outwards side.  ie Supply and Load

Also circuits back feeding onto the grid from micro generation like Solar PV or Car2Grid (other names are available)

youtu.be/r7eWUJoe5mI

youtu.be/r7eWUJoe5mI

I've dismantled quite a few to see what the directional dependant features are.

At the outset the T button was on my list of concerns - most seem to use 2x 4.7k 1206 resistors in series. These are rated 0.25W each. So they're 1/10th the necessary rating, which is absolutely fine if the RCD interrupts them but not okay if it can't.

Curiously several RCBOs - especially budget ones like Fusebox - have the T button arranged between L on the incoming side and N on the outgoing side. This is contrary to the little diagram on the side of the device. Of course this means that in those cases the T button would be fine. But in e.g. Hagers miniature RCBOs it wouldn't be - Hager are single pole so they couldn't pull this trick.

In terms of ability to withstand being powered from downstream - I've not found any that should have too much problem as they all have quite robust input protection. However I if this circuit did develop a fault then it's protected by the fault coil on the MCB function - whereas if it was fed downstream it wouldn't.

But then vast majority of these applications the downstream has e.g. ROCOF protection.

But there's a big unresolved issue - what should be the overarching principles for protection of generators in these applications? The regs -  even in Part 8 - just don't give a satisfactory treatment. Worse still most inverters have very poor MIs when it comes to the protection of their terminals - what is the prospective fault current at a PV inverters terminals? The manufacturer doesn't usually know.

I'm not sure why this is being billed as an emergency amendment. Where's the evidence to back up that this is causing sufficient risk? Presumably if it was a risk then there would be evidence of incidents stemming from it given people have been connecting PV systems to RCBOs for a very long time - maybe the hazard is a novel one due to islanding mode?

Seems to have now been posted to BSI, comprising the changes suggested by Lyle and Andy (I haven't checked if they are verbatim).

If this is all it is... I confess I need to check the books but is this not already a requirement?

Also, to have been rushed out in this fashion, presumably this is in response to a specific incident(s)? Either way would it not be reasonable for BSI/IET to publish a supporting note justifying the change; this should illustrate where there is a (percieved) deficiency / gap in the existing standard.

Technical question wth regards to Amendment 3.
Will this be classed as a C1 or C2 on an EICR if a Unidirectional is fitted rather than a Bi-Direction if it is fitted to Micro-Generation like a Car2Grid or when doing PV to Grid?  Also would it require a replacement breaker as the wording in the proposed Regulation states SHALL?  

Sorry have just gone back and looked, the IET say on the BS7671 portal

The amendment follows a bulletin from BEAMA which aimed to clarify the differences between connections for unidirectional and bidirectional RCDs and circuit-breakers.

which would appear to refer to this

https://www.beama.org.uk/resourceLibrary/beama-technical-bulletin---connection-of-unidirectional-and-bidirectional-protective-devices.html

Jam said:

is this not already a requirement?

There are various provisions already in, for example, §551 covering RCDs and OCPDs not backfeeding devices marked in a unidirectional fashion... I think these are what I was thinking of.

It strikes me that issues with the Test button are rather unlikely in practice.  All grid-tied micro-generators are required to shut down within a few seconds if the grid power goes off.

So someone would have to disconnect the supply, and then immediately poke the Test button on an RCD or RCBO to cause a problem.

Will this be classed as a C1 or C2 on an EICR if a Unidirectional is fitted rather than a Bi-Direction if it is fitted to Micro-Generation like a Car2Grid or when doing PV to Grid?  Also would it require a replacement breaker as the wording in the proposed Regulation states SHALL?  

Or maybe just a C3, or NOTE? I don't think the SHALL word is that significant - 514.4.4 says shall for colour coding, but I don't think anyone's ever suggested we need to rip out all the red & black cables and replace them with brown & blue, or even code them C1 or C2 just because of their colour.

   - Andy.