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

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,

I thinks that's what 536.4.201 is trying to say - although I'd agree not very clearly. (BTW I think things have moved on an it's now Annexe ZB of BS EN 61439-3)

   - Andy.

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.

The one you see in the image Andy is just the secondary one. We also have one at the meter which is at the top of the driveway. A secondary one was fitted alongside the main board just to stop me having to walk all the way up to the top of the driveway in order to reset it if that one trips. This one will trip before the one at the meter does but as I say, we get a lot of nuisance tripping with it. 

Wondering if we should just take it out and I leave a pair of hiking boots by the door instead . #justbeinglazy 

First step - can you get us a pic of the writing on the one that trips, and also of the one at the end of the drive, that does now, then we know if it is an RCD or an RCBO or something more complex with a maximum load -limit function. Then we can give you more informed unhelpful advice... And even if there is no simple answer it is good to know why.
Mike.

There are a variety of verbs in French that can all be translated as off and on so I guess they use the English version to be consistent with electrics. Much like their Stop signs that say 'Stop' and not 'Arret' . They do actually use and say 'stop' in general conversation too . 

Thanks Mike, I'll have to get back to you on this though as I'm back in the UK at the moment so not able to take a pic!

If it helps I managed to extract this from Lisa's original picture:

Looks to me like a 500mA with a 45A load trip setting. Doesn't help with the settings on the upstream unit of course...

   - Andy.