I have read what you have written:
Say the garage spur is loaded to 20 amps, the ring then is restricted in capacity as there is only 12A remainig until the mcb trips.
That is perfectly true - if you load the spur to 20A then the ring is restricted in capacity as there's only 12A remaining.
But the same applies with any
spur loaded to 20A, or indeed if any socket is loaded to 20A - there's still only 12A remaining for all the other sockets.
And when I pointed that out, you wrote:
You should read what was written. A ring can pass 32A, using a spur from the same 32A mcb that draws 20A means the ring can't reach its capacity of 32A. That means if high current appliances are used on the ring, say a kitchen ring, then the 32A mcb will trip.
Read the thread again. It is easier that way.
Which did seem to me to indicate disagreement, i.e. that you believed that a spur taken from the ring at the MCB somehow had a different effect on the capacity available to all the other sockets on the ring than a spur taken from a different place or, indeed, if that 20A was being drawn from one of the ring sockets.
If I'm wrong in that, i.e. you weren't
disagreeing, and that you do
accept that there are no special concerns, or differences, with a spur taken from the point where the ring passes through the MCB then fine.
But if you are disagreeing, and you do think that there are special concerns or differences then I think it reasonable to ask you to explain why, because I can't see what they might be.
Or if anybody else reading this can explain, that would be useful.
The questions are:
- How spurring from a ring at the MCB is any different from spurring at any other point.
- How taking 20A from any spur on the ring has a different effect on the capacity available for use by all the other sockets and spurs than does taking 20A from a socket on the ring.
- Why, therefore, the situation described is different from plugging those same items into any double socket on the ring and drawing 20A from it.