distance d\'ouverture des contacts de tous les pôles

22:32 Nov 6, 2018 

Yes, gap is applicable for contacts. Clearance has a similar meaning, but refers mainly to fixed live parts. See the list of all IEC standardized terms containing "clearances":
http://www.electropedia.org/iev/iev.nsf/SearchView?SearchVie... You can verify this by clicking on the numbers.

Kim's link confirms this even not shown. If you open the link you will see the following terms:
EN switch of mini-gap construction
FR interrupteur à faible distance d'ouverture des contacts
Unfortunately he copied only the definitions, but not the terms.

19:58 Nov 6, 2018 

Ok thank you Tony for the further explanation.

18:42 Nov 6, 2018 

As I have explained, 'intervalle' as suggested by Johannes is applicable where we are talking about the physical characteristics, dimensions, etc. of the actual gap.
But here, the notion of 'distance' (note the absence of any further qualification) IMHO is trying to say that there must be physically separated contacts — there must be a 'space' between them, which is referred to as the 'contact gap'.
What you have here is a situation where we are not discussing the characteristics of said gap, but simply the fact that one must exist.
This is relevant, and basically means there must be an actual physical, mechanical disconnection for isolation purposes; these days, for merel switching something on and off, a solid-state relay is often used, where the "isolating" components are semi-conductors; this has the huge advantage of no moving parts to wear out or go wrong — BUT it does not provide "proper" total isolation — some current could still leak through, especially in the event of a fault!
Certain types fo isolating devices have what is called a 'visible break' — you must be able to actually literally see the gap between the contacts.

18:19 Nov 6, 2018 

Switch construction having a clearance between the open contacts which is 1,2 mm or greater and meeting the performance requirements for mini-gap construction

Interrupteur ayant une distance d'isolement dans l'air entre les contacts ouverts au moins égale à 1,2 mm, et satisfaisant aux exigences de fonctionnement pour la construction à faible distance d'ouverture des contacts
http://std.iec.ch/terms/terms.nsf/9bc7f244dab1a789c125705900...

18:09 Nov 6, 2018 

I wonder why they have used the French I have cited in the source rather than the standard "intervalle" then?? Could this entail a different translation or do you think "contact gap" still fits the terms I have in my question?

18:07 Nov 6, 2018 

Point taken regarding "mandatory" - you're right. I got fed up with all the "musts" in this translation but you are correct that there is a nuance here and it should (or must?) be "must" here too! Your comment at 2) is helpful as well, I found a translation using "circuit-breaker" for the French used here but would prefer the generics you suggest to avoid being over specific.

18:05 Nov 6, 2018 

There are some problems with your proposed translation:

1) We are not talking here about anything 'mandatory' — this is a simple 'must'
2) It is not correct to use 'circuit-breaker' — this amounts to over-interpretation of the source text, which just says 'a means of disconnecting' — which could be achieved by several different types of device other than a C/B. I would just say soemthing like 'means of disconnecting...' or 'disconnection device'; at a push, you might use 'isolating device', since that is in effect what is going on here.
3) See my comment to Chris C. as to why they are talking about 'physically opening contacts'.

18:01 Nov 6, 2018 

I think what they mean is there must be a physical air gap for ALL poles (i.e. L + N, or 3-ph + N), and it mustn't be a solid-state relay.

17:44 Nov 6, 2018 

Although there seems to be a word missing from qualifying "distance" (suffisante, adéquate...?), the idea seems to be that the distance between the contacts must be sufficiently great to prevent arcing, say, or some inadvertent or accidental connection.