Re BS Standards for Distribution boards and Enclosures

Distribution boards aren't cheap, nor are their sub circuit protection componants. We have old square D boards installed in the early 90s and we just obtain the Schneider equivalent if we need to add or alter a circuit to bring it in line with current standards.BS7671 will determine whether or not you need to change the likes of a mcb to a rcbo, or in the case of three phase circuits, just ad RCD protection via an external enclosure adjacent to the dist board.

Question 1 is rather vaugue - what are you defining as 'impact'? Number of spare ways left? Future capacity/loading?

Question 2 - the answer is the requirements of BS7671 which you should be familiar with if you are undertaking this kind of work.

Question 3 the answer is yes if available and the board/range isn't obsolete.

There are several questions here. I will kick off but others will no doubt spot things i have forgotten.

1)  Re 40 year old breakers to previous standards.  There is a broad overlap in the tripping speeds, but you may find in marginal cases, that the circuit is a bit frisker to disconnect with a new breaker than it once was, or that inrush that never matterd before now does.
how well do you know the history, in the sense of have they ever been called upon to trip, have there been any failures to trip, and is the environment cool, clean dry ? Contacts degrade with tripping, but in all devices lubricants in mechanisms slowly stiffen and if things never move, then sliding shiny parts slowly oxidise and become rough and may fail to operate when they should or perhaps even at all.  Damp induced corrosion I hope needs no explanation.
If the answer is anything other than these are perfect its probably time for a change.
2) RCDs. This is where the regs have changed over the years, and are now considerably more demanding. If in doubt look at your copy of the regs but basically, since 1989 we now have wiring routing rules, and wiring that is concealed and not armoured or in metal conduit needs to be RCD protected, all socket circuits for portable kit less than 63A needs RCD protection and circuits that may not always meet disconnection times due to length, may use an RCD to provide fault detection.  Note that there are  a few  of types of RCD, with varying performance for simple resistive and electronic faults, and the old AC only type is generally deprecated.

3) swaps of giblets. 
It is not guaranteed to fit - there is no standardization of contact positions and mounting offsets, even for older offerings from any one maker, let alone between different makers . If you do, you have to be happy that you have become the designer of the new enclosure and are adopting legal responsibility for its safe operation. Unless you are very confident, and ideally have the makers approval, the advice has to be no for anything more than an expedient fix to keep something running. As it may well involve moving DIN rails and bus bars, it may well not even be any cheaper. Of course if the maker is still in business and says its OK, or even makes an upgrade kit, just go for it.

regards Mike

I am not clear on what you are proposing to do.

If you mix and match, you become the manufacturer of the board and, accordingly, responsible for ensuring that it meets all the requirements of BS EN IEC 61439-3. That may be difficult if some of the parts are to BS 60439-3.

See Note 2 to 536.4.203.

 using the present array of MCB's within the current Distribution boards which are some 30-40 years old in line with what the current standards BS EN 61439-3 compared to the old Standards BS EN 60439-3?

The standards for MCB (and RCCBs/RCBOs) are somewhat independent of the standard for DB that they go into - as far as I recall BS EN 60898 MCBs went into both BS EN 60439 and BS EN 61439 assemblies (although looking back 40-ish years there was an older standard BS 3871 for MCBs and many devices were stamped according to both standards during transition). All standards undergo regular revisions every so many years though - so there may be a more (to you) significant difference between two versions of the same standard (e.g. BS EN 61439-3:2024 and BS EN 61439-3:2012) as there was between one numbered standard and its differently numbered replacement (e.g. BS EN 61439-3:2012 and BS EN 60439-3:1991).

The compatibility between an enclosure and the devices within it, unfortunately, aren't a matter for standards - but are left to individual manufacturers - over time we've seen manufacturers change their range of MCBs and enclosures such that the old MCBs won't fir the new enclosures or vice versa even though everything was to the same standards as before. Mostly manufacturers only condone using their devices (and from the same range) in their DBs.

 - Andy.

AJJewsbury said:

The compatibility between an enclosure and the devices within it, unfortunately, aren't a matter for standards

Except, perhaps, for consumer units and similar distribution boards, where the 16 kA conditional short-circuit test for the UK applies.

It sort of means that, unless a manufacturer can confirm no material changes between one product range and its replacements over time, all a manufacturer could say is "not guaranteed to be compatible".

Basically the idea was rather than replace the distribution board could we use the existing board and replace the old MCBs with the modern equivalent MCB.

The reason for this is that the existing board we are struggling to find the exact equivalent board that matches in dimensions. As we are concluding that it could be bespoke and not a COTS board. 

The reason for this idea is that we believe that the distribution board was bespoke and not COTS type of board so finding the correct dimensions required for the board to instead use the existing board but wasn't sure whether this would be of correct practice. 

Is the manufacturer of the bespoke boards (or a company that bought them out) still in business? If so, can they comment?

This type of thing comes up all of the time with larger switchboards, where someone (even if it's another switchboard manufacturer) will have to take responsibility if a spare compartment is to be kitted out.

Whichever you go for, someone will have to take responsibility for the updated distribution board.

Indeed - but I meant more generally you can't just replace an old BS EN 60898 device with a new BS EN 60898 device and expect it to fit/work/be-safe - all sort of things may differ between brands or ranges (or just over time) - not just obvious things like position of terminals and heights above DIN rails, that standards could have easily addressed but haven't - but things like heat dissipation. The 16kA is an extreme case where your using components outside of their individual specifications (e.g. 6kA MCBs for a 16kA fault situation) so you need some extra "margin" that the manufacturer has go get from somewhere, but even in less demanding situations there are lots of incompatibilities that the standard simply don't address.

   - Andy.