314.4 sets out the requirement to connect each final circuit to a separate way in a distribution board. A split board provides that.

314.1 indent (i) sets out two of the reasons why installations should be divided into circuits, one of which is to minimize inconvenience in the event of a fault. The notion of "inconvenience" is a subjective one. It could be contended that the only person able to make that call would be the user of the installation. Without the input of the user, a designer could only speculate on what would cause "inconvenience". However, if it is established that inconvenience could be caused by the tripping of more than one circuit because of a fault, then the next step is ensure that the "inconvenience" is "minimized".

To "minimize" something is to reduce it to the lowest possible degree. If the user or designer considers multiple circuit disconnection in the event of fault would be an inconvenience then the designer must "minimize" that possibility.  A split board arrangement would not provide that and would therefore not meet 314.1 indent (i).

There is nothing in 314.1 about cost. It is a "shall" regulation.

Any one wishing to explore the meaning of "inconvenience" might like to ask folk in Manchester (today around 3pm) if it would be "inconvenient" if a fault in their kettle also disconnected their TV!

To "minimize" something is to reduce it to the lowest possible degree.

But not necessarily without regard to all other factors - e.g.. acceptable cost. That's why it's minimised rather than eliminated,

  - Andy.

Any one wishing to explore the meaning of "inconvenience" might like to ask folk in Manchester (today around 3pm) if it would be "inconvenient" if a fault in their kettle also disconnected their TV!

In which case, one final circuit for each socket? .. and only single socket outlets allowed.

Curiously before these modern fads of RCDs and circuit breakers, a 13A plug fuse discriminated very nicely with a ring 30A fuse, which in turn discriminated very nicely with a 60A+ DNO fuse - so selectivity even between appliances on the same circuit was pretty much guaranteed. Nowadays with a B32 RCBO tripping faster than a 13A fuse, it's a case of one out all out. That's progress for you....

   - Andy.

"The designer must "minimize" that ,,, nothing in 314.1 about cost. It is a "shall" regulation."

I take the point, and have RCBOs in a flat that we rent out, but an RCD here where I am near enough to reset it.

However, the counter argument is that one could raise similar assumptions about the  "inconvenience" at any price of not having a private substation, not having multiple incomer feeds, or a back up DRUPS, or even not having a small on-site nuclear facility in the grounds...

  Now at quite different price points, all of these make sense and are appropriate solutions, though the last probably only at govt agency level, as there are problems with the regulations around moving the fuel and the waste, (not the physics mind you) but the domestic installer world does not rewire a former council flat at all beyond a certain price point.

So regardless of the exact form of words in a non-binding British Standard,  there will actually be a limit.  It may still be that for some that limit is indeed  found with one RCD covering the whole installation or large chunks of it.  And there will be a good no, of folk who are not unduly worried about losing the footy who will be doing something else instead. 

Personally I'd be more worried about the loss of tea supply, and to that end I would  deploy the back-up kettle - and in a full street power cut, I have a further level of defence in the form of one that goes on the camping gas stove or in winter on the fire in living room

The political/ economic  meaning of minimize is not the same as the pure maths - what is really minimized is some sort of cost-effort- inconvenience blended quantity, if we like it or not,

Mike

lyledunn said:

To "minimize" something is to reduce it to the lowest possible degree. If the user or designer considers multiple circuit disconnection in the event of fault would be an inconvenience then the designer must "minimize" that possibility. 

If we take this is interpretation to its conclusion, one circuit per appliance or item of current-using equipment is necessary to reduce inconvenience to its lowest possible degree.

I therefore conclude this is interpretation is not what is meant (although only a court in the end could decide that).

lyledunn said:

A split board arrangement would not provide that and would therefore not meet 314.1 indent (i).

I therefore don't agree with this statement but it's subject to a court's decision.

Would custom and practice therefore provide an argument for an interpretation that did permit a split-load board interpretation of 314.1 (i) ?

I would add, though, that custom and practice is changing.

Whilst many existing installations operate satisfactorily with split-load board, it is not likely to be suitable when we start adding EV charging, induction hobs, heat pumps, etc.

gkenyon said:

If we take this is interpretation to its conclusion, one circuit per appliance or item of current-using equipment is necessary to reduce inconvenience to its lowest possible degree.

I therefore conclude this is interpretation is not what is meant (although only a court in the end could decide that).

Ah, but I think that a court (or tribunal) would look at the lowest reasonable degree.

Chris Pearson said:

Ah, but I think that a court (or tribunal) would look at the lowest reasonable degree.

And then, isn't it a matter of opinion what is "reasonable" ? I don't think that

Consider that a split-load board offers isolation of all live conductors for a group of circuits whilst permitting another group of circuits to remain energized, whereas with an RCBO-board, the neutral is not isolated, so from a safety perspective, it might be considered a better solution to work on part of an installation? Which "reasonably" will you look at then? "Reasonably practicable" vs "lowest reasonable degree"?

And then, in a solution where the neutral is not at least switched off when there's a fault, a N-E fault in an appliance (or the installation) isn't addressed by the single-pole switched RCBO "to minimize convenience" ...

Obviously, a solution that offers the benefits of both (2-pole switched RCBO or full 2-pole RCBO) would be a solution that deals with both?

Where do we stop? The devices are available to do it?

Or, are you arguing that all single-phase domestic CUs now need to have 2-pole switched RCBOs because of the possibility of N-E faults not clearing faults?

gkenyon said:

Or, are you arguing that all single-phase domestic CUs now need to have 2-pole switched RCBOs because of the possibility of N-E faults not clearing faults?

It is precisely this issue, which stops me from accepting the argument that "split-load is bad because we now have RCBOs".

That argument would only be true if we were to use 2-pole switched, or full 2-pole, RCBOs - but we are fitting single-pole switched RCBOs and ignoring credible fault scenarios that the split-load would address.

whereas with an RCBO-board, the neutral is not isolated

Or more precisely, on SOME RCBO-boards, the neutral is not isolated - N switching single module  RCBOs have been available for quite a few years now - and some of us have much preferred them for the reasons you mention.

   - Andy.

gkenyon said:

And then, isn't it a matter of opinion what is "reasonable" ? I don't think that

gkenyon said:

Or, are you arguing that all single-phase domestic CUs now need to have 2-pole switched RCBOs because of the possibility of N-E faults not clearing faults?

I would suggest that a court (or tribunal's) decision is always a matter of opinion.

No. To the contrary: what is reasonable to do? I think that the primary concern is always what can the customer afford? So the contractor should give a range of options and explain the benefits and risks of each.

gkenyon said:

And then, isn't it a matter of opinion what is "reasonable" ? I don't think that

gkenyon said:

Or, are you arguing that all single-phase domestic CUs now need to have 2-pole switched RCBOs because of the possibility of N-E faults not clearing faults?

I would suggest that a court (or tribunal's) decision is always a matter of opinion.

No. To the contrary: what is reasonable to do? I think that the primary concern is always what can the customer afford? So the contractor should give a range of options and explain the benefits and risks of each.