On 27/05/15 22:31, GB wrote:
If there are no glitches in the wiring that is carried over two cables
with a minimum current carrying capacity of 20A each, ie 40A total? So,
there is a bit of a safety margin.

Nope.

If the two lengths of cable feeding a given socket are of unequal
length, more current will go via the shorter (lower resistance) route in
proportion to the difference in length (in resistance, in fact).
The only way a ruing contributes to anything is by providing alternate
earth paths, and in the case of many distributed loads, slightly easing
current requirements, but anyone who fuses a ring at more than the
capacity of a single wire in the ring is a fool.


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