Steve Jones wrote:
Before my post yesterday about ring or radial for garage sockets I
assumed that I needed either a 2.5mmsq ring circuit or a 6mmsq radial
circuit. But one answer I received suggested that a 2.5mmsq radial would
suffice.

Wanting to understand this better I have spent quite some time this
morning looking on the Internet. My new understanding is:

Ring Circuit, 2.5mmsq, 32amp MCB, maximum floor area of 100sq m

Radial Circuit, 2.5mmsq, 20amp MCB, maximum floor area of 20sq m

Radial Circuit, 4mmsq, 32amp MCB, maximum floor area of 60sq m

These are the 'conventional circuits for BS1363 sockets' listed in one
of the appendices of the IEE 'On-site Guide' so, yes, these are pretty
certain to be allowed by the IEE regulations. However I believe the
floor areas you have given above are somewhat out of date, if memory
serves me correctly they are now 100sq m, 50sq m and 75sq m
respectively. The floor areas are only recommendations really.



Can someone give a concise description of why this is so? How is this
calculated? I would love to understand this fully.

What are you trying to understand exactly? The above circuit layouts
are practical and (unless taken to extremes in wierd ways) will
conform to regulations regarding voltage drop, earth loop impedance,
etc.

--
Chris Green