Continental Europe it's common practice to use wire links in consumer units whereas the British practice is to use a rigid live busbar, although dual live neutral busbars are also common in Continental Europe. This possibly helps to explain why mixing protective devices from different manufacturers is more commonplace in Continental Europe than in Britain.

The other difference is that the UK tend to have low impedance single phase supplies with correspondingly high prospective fault currents - e.g. 16kA - whereas our continental cousins tend to have much lower ratings per phase so thinner supply conductors and lower PFC - for domestics at least they normally wouldn't have to deal with anything over 3kA - certainly not over 6kA - all within the capabilities of individual MCBs. Whereas we need a UK specific annexe to the standard with lots of ifs and buts to somehow get a 6kA MCB to work with a 16kA fault current - and one approach to that is to make sure that anything (e.g. products of arcing) that escape the MCB are safely contained within the enclosure - which does require a bit more co-ordination between box and module than it physically fits.

    - Andy.

Which would be fine if we made that clear and very specifically required type approved assemblies with supplies with a PSSC exceeding that of the weakest breaker, but it is rare to see that distinction made clearly. 

Also even in the UK a great many settings with domestic style CUs never see anything like a true 6kA PSSC, let alone a 16kA one, and the situation of an exploding MCB or RCBO being saved by the prompt actions of the BS88 style company fuse is a pretty extreme corner case. I suspect truly faulty breakers are more likely.  60439-3 Annex ZA does exists, but we do not often need to invoke it.
There is a reason that the millions of hot wire fuses were never really a problem despite a name plate breaking rating of 3kA or less...

(and for wire tails to things like bell transformers inside a CU, but behind a suitable MCB, what is the real problem ?)
Mike

Every now and again, when I walk past the house a couple of doors down on the other side, I wonder what their PSSC might be because they are next to the transformer. Ours is about 1kA.

Terraced houses with front doors directly on to the street might be slightly different.

1KA sounds entirely credible, and perfectly adequate. Do not get me wrong, I'm not saying we do not need the conditions of Annex ZA ever, but probably not as often as the more desk bound reg-writers may imagine. I'm a great fan of writing in felt tip on the meter board 3 things, the company fuse rating, assuming that I may have seen it (!), the Zs and the type of earthing -i.e. 100A/ 0.18 ohms/ TN-s or  80A/0.32 ohm/PME That kind of thing - and from  memory those are the right sort of numbers,  I'm struggling to recall ever finding much less than 0.1 ohms - i.e. a PSSC of 2,3kA  in any under-stairs cupboard type of domestic setting.

Now I'd be the first to say that do not do this very often or  at all these days, and also I am not in a city - the substations will be 400A or perhaps 800A per phase units, with 50-80 houses per phase and the odd 3 phase corner shop or village hall, maybe a hairdressers, no more. 

If the transformer manages 5% drop at 800A, then at short circuit you may expect 16kA there, sure, but that is a "silver spanner" fault at the substation, as soon you back down the wire you do not need many metres of cable to affect the answer - even if each house is on a 10m long branch of 35mm2 concentric, even direct from the transformer,  that is an extra 15- 20 milliohms straight away, and most will be a tap after some length of street main, not transformer direct.
Our scout HQ has the substation fenced in on the other side of the car park, about 20m away from the intake, yet the  Zs is never less than 0.12 ohms despite the 3 phase 100A supply. I'm not sure if the route takes a specially long loop underground somewhere...
Mike

mapj1 said:

Our scout HQ has the substation fenced in on the other side of the car park, about 20m away from the intake, yet the  Zs is never less than 0.12 ohms despite the 3 phase 100A supply. I'm not sure if the route takes a specially long loop underground somewhere...

May be! Our main goes past the front gate, along the street to the bottom of the garden and then turns left until it gets to the back of our plot where the service cable branches off for another 10 m or so. Perhaps it is because the house has not only changed its name, but also its address.

mapj1 said:

Our scout HQ has the substation fenced in on the other side of the car park, about 20m away from the intake, yet the  Zs is never less than 0.12 ohms despite the 3 phase 100A supply. I'm not sure if the route takes a specially long loop underground somewhere...

May be! Our main goes past the front gate, along the street to the bottom of the garden and then turns left until it gets to the back of our plot where the service cable branches off for another 10 m or so. Perhaps it is because the house has not only changed its name, but also its address.