An interesting point made by one of my colleagues today.
If we consider a 36-way TPN distribution board that is full. How can we apply a grouping factor to those circuits at the point they leave the distribution board (the worst case position) without it making the cables so large that they can't be terminated if some of them are lighting or ring final circuits installed in trunking?
Clearly we could use sub-distribution, etc. but I have seen plenty of installations exactly like this with fairly typical 2.5sqmm or 4.0sqmm cables on the lighting and ring circuits.
Is it simply that the point of exiting the board is ignored and the main run of the cable is used for consideration of the grouping factor? If the cables are de-rated on the basis of where they come together at the board how does any installation ever practically make use of a 36-way TPN board without substantially over-sizing cables?