There are various provisions already in, for example, §551 covering RCDs and OCPDs not backfeeding devices marked in a unidirectional fashion...

where abouts? (I'm probably being dim again...)

   - Andy.

AJJewsbury said:

does this cover my simple PV system?

More than likely, yes.

AJJewsbury said:

So not bi-directional?

Well, no, bi-directional. A fault in that circuit be fed from either side, and in theory, power could flow either way ... most importantly, even if only for a (potentially very short) time, power will be available on live conductors on both sides of the device even if it operates (with an RCD, say, even when the test button is pressed).

Yes, 826.1.2.2 "Selection and erection of overcurrent protective devices shall take account of all possible directions of current flow and polarity.".

Part 8 deals with the particular cases of embedded generation where bi-directional flow is likely to occur.

But whilst the fault current from the grid is typically in the kA region, the maximum short circuit that an inverter can feed is mentioned in it's datasheet and typically <=32A.

If you look in BS EN 61009-1 at the tests that are different for bi-directional devices - they are only tested differently to unidirectional devices for the detemination of Isc and Icn [9.12.11.4 b)1)  & c) respectively].

It follows that if you know the maximum short circuit current that can flow upstream through a device is < 1.5kA then it makes no difference.

Interestingly bi-directional devices aren't - according to EN 61009-1 - actually functionally tested in all 4 quadrants other than for Isc and Icn.

lyledunn said:

So is this an emergency amendment?

There is not, strictly, such a thing as an "emergency amendment" defined in BSI's rules, and BS 0. Quite simply, it can't be considered a 'Corrigendum' because it doesn't meet the criteria, but it is a sufficiently small change to render the much longer timescale usually required for more extensive amendments, new editions, or revisions, unnecessary.

lyledunn said:

As it’s the third amendment, does that mean a 19th is more likely to be sooner than expected?

I'm sure I posted something on LinkedIn over the weekend, that speculation in this regard would be running rife (whether it would be a 'revision', 'new edition', or an 'amendment') ... I'm sure we will hear about how any subsequent Amendment is to be handled by press release at the appropriate time.

Well, no, bi-directional. A fault in that circuit be fed from either side, and in theory, power could flow either way ... most importantly, even if only for a (potentially very short) time, power will be available on live conductors on both sides of the device even if it operates

That seems to be a different definition again - power being available (i.e. voltage present?) isn't quite the same as power flowing, especially when the device is open.  That would seem to catch cases where there's individual protection to parallel conductors of the like shown in appendix 10 - with the typical arrangement of nothing but loads on the load end, I'm not sure many would have thought that it constituted bi-directional power flow - especially for the supply end devices, yet when the first device opens there'll be voltage on both sets of terminals.

  - Andy.

826.1.2.2

But it seems that not every installation that containing local generation would be a PEI and subject to part 8 - a simple (inverter only) PV system simply injects all available power into the system - regardless of the needs of the local installation or indeed the wider grid. It has no management system. Thus it seems to not meet the requirements for a PEI (e.g. 823 (iv) or 822.1).

Presumably the implication is that the new requirements apply not just to the PV circuit itself, but also everything that connects it back to the grid (presuming it's capable of export at times).

So this incomer would be a problem:

  - Andy.

In relation to that proteus main switch, it's not a protective device so I don't think it would be captured.

But I've done some survey of the standards and the language about directionality changes between them. Notably MCCBs have to use an arrow symbol and not the words "supply" & "load".

One concern I've got is that the underpinning standards only make fleeting references to directionality and have poor definitions of what directionality in fact is. For example any AC load at non-unity power factor technically has bidirectional flow of power and it would be a more natural use of language to refer to these devices as been uni/bi-directional in respect to flow of energy.

I think we can categorised the concerns into the following broad classes:

1) are the devices able to interrupt a fault current in the reverse direction without suffering damage? This appears very difficult to achieve because the electronics must withstand the Isb [>6kA] being interrupted adjacent and causing a very large transient right on its terminals likely far exceeding the surge arrestors capability.

2) are the devices able to interrupt a residual current in both orientations? This appears trivial - hence almost every RCCB on the market presently is already bidirectional.

3) are the devices likely to give rise to a hazard if fed from the "load" side? This is a potential concern but it's not actually addressed in the product standards - it's quite possible that there's bidirectional RCBOs out there that could for example develop an internal fault which depends on MCB function to interrupt and therefore could be hazardous in these appliancations - this proposed ammendment does nothing about this problem and if anything it could create false security. My gut is that we should ensure any source of power has sufficient protection at it's terminals to protect against this kind of fault - but that's not trivial either because inverters have a relatively low short circuit current so how can you protect against an L-L fault when the Ipf is in say 32A?

I'm wondering what evidence such as incident reports there are behind this proposal - BEAMAs report notably lacks case studies.

gkenyon said:

. I'm sure we will hear about how any subsequent Amendment is to be handled by press release at the appropriate time

From debate here a few years ago,( maybe from you?), I was under the impression that there can only be 3 amendments, any more have to be a new edition, the thinking came from either BS, or maybe IEC standards.

Is that still the case, or could there be a 4th Amendment of the 18th?

In relation to that proteus main switch, it's not a protective device so I don't think it would be captured.

The proposed 530.3.201 seems to include "equipment for protection, isolation, switching, control and monitoring".

I have a feeling that a lots of devices got labelled supply/load not because of any physical limitation of the device, but more as a convenience to the installer (so when in place in a typical CU the terminals would have helpful labels) or indeed the manufacturer (saves having to put the labels on the CU part of the assembly or have an extra manufacturing step to label the devices after insertion).

   - Andy.