R W wrote:

Andrew Gabriel wrote:

In article ,
Dave Plowman writes:

In article ,
The Natural Philosopher wrote:

OTOH are you sure that you haven't come across a bit of the old
7/029 used around then - seven strands of 29 thou copper that was
usually tin plated - this was a pre-metrication standard.


ISTR that was pretty standard in most house in the '15A round pin
plug ' era...

It was also used for the best part of 20 years for ring mains, too.

Yes -- one of the design aims of the 30A ring circuit was easy
conversion from a 15A radial system (by making the ring start
and end at two existing 15A outlets, converted to 13A of course).
Hence the two schemes used the same cable (and you were allowed
to keep the two 15A fuses at each end of the ring early on too).


What's the story behind the switch from 15A to 13A sockets? Surely 15A
would be more useful....?






I am not sure. The technology was sold to and continues to be used in south africa.


The square pin is allegedly easier to make a decent high current self
wiping contact with than the old round pins, and I suspect what happened
was somethig like this.

(i) let's move to ring mains cos we need a LOT of sockets these days,
and we can't radial wire them all, and ringing them is a bit safer and
relaxes cable constraints.

(ii) let's go to a new and better type of plug.

(iii) now each appliance has its own plug, rather than one socket per
room (or floor?), how much do we realistically need to rate a single
point at...3KW sounds nice. Oh. Thats 13A then? Right. 13A it is...

(iv) Mmm. What will the cable stand. Ok, about 30A seems right for the
sort of cable that isn't TOO heavy. Lets standardise on 30A or 32A fuses
then.

(v) what about lights? Oh sod it. do them on spurs cos they are always a
nightmare with cables flkying everywhere, and you seldomn need a lot of
current for em. say fused at 6A - that is 12 x100w bulbs,. Thats plenty
for a house.

(vi) What about all these other plugs and sockets? Oh sell em to someone
who wants em. Africans will do.

(viii) I need to set up sockets for msall lamps on lighting
circuits...oh well use teh 5A old style plugs if you must. At least
people won't be able to plug cookers into em. and they shold take 6A
before the MCB trips.