Does a split board strictly comply with the Regulations, should we have RCBO's?
Does a split board strictly comply with the Regulations, should we have RCBO's?
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.
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?
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.
Not exactly a split board but the designer of this distribution arrangement in a church and adjoining hall seems to be stretching semantics. His idea of “minimise” doesn’t square with mine. Every socket circuit in the complex is on the top board which has a 63A 30mA type AC RCD overall. The connectors evident in the top board re-direct the supply to the septic tank which was originally on the socket board but was found to be the cause of multiple tripping events, often interrupting church services and social gatherings.
Maybe the contractor could counter that he was only being frugal!
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.
It does make one question the value of requirements within a standard that contain verbal forms such as:
etc.
It's not so much that the intent or sentiment is not understood, but the fact that, for verification purposes, it's not easy to provide an interpretation as to whether the requirement has been satisfied or not by a particular design.
Pedantically, when looking at whether a standard such as BS 7671 has been satisfied, the first thing that ought to happen is each and every clause of the standard ought to be validated, i.e. the question answered "Does it apply to this particular design, and, if so, to what extent?"
Consider a simple example. Regulation 411.3.3 - if there are no socket-outlets rated at 32 A or less in the installation, and no outdoor equipment, the requirement is not applicable to that installation.
However, more complicated is Part 3, because Part 3 sets out fundamental requirements, which are addressed by applying Parts 4, 5, 7 and 8, which are in turn verified by a statement of conformity by the Designer after assessing the fundamental principles (131 and 311 to 313, see 641.2). In the case of the topic of this thread, this is not discussed in sufficient detail in Parts 4, 5, 7 and 8, for us to have a better clue from the remainder of BS 7671 as to whether a split-load board is considered adequate ... and of course that is because in one installation, it might be, and in another, it might not.
As to who carries out this requirements validation process (inspector or designer)? I would say designer, but what if the inspector and/or Client don't agree with the designer? It's easier in a large commercial contract in which the Client will have one or more persons agreeing designs and requirements validation exercises. In larger projects, design is done in stages, and not always by the same legal entity at each stage.
In reality, the enormity if the task at hand (validating 300+ pages of requirements) means it never happens, and I would think that most topics like the one being discussed in this thread are only ever simply something for guidance, rather than considering each installation on is merits - and leaving the reality that such questions are only ever properly answered if they become part of a legal case (criminal prosecution, or civil proceeding that might yield a large enough payout for one side to make it worth going to court and being discussed there).
And then, isn't it a matter of opinion what is "reasonable" ? I don't think that
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.
That looks terribly domestic!
For a church it looks terribly good ;-) Maybe I'm unlucky but there are usually 'Old Bill' switchger with hot wire fuses and TT mains with no RCD in the ones I seem to spot on ringing outings. The trick I find is to feign ignorance so long as the lights stay on for the duration of the visit.
Mike
PS Still that one seems to be due an inspection in 2008 - so the right century at least.
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