NT wrote:

On Mar 9, 10:00 am, (A.Lee) wrote:

There is speculation on why we have the 5 seconds disconnection rule for
distribution circuits - far too long, and pretty unsafe if you drill
through it, and the usual answer is that there were so many fuses out
there, British manufacturing couldnt make a Breaker to meet the 0.4
second rule,

Its trivial to make a breaker that acts wthin 0.4 seconds. The
mechanism is the same as a relay. Its not done because its not
desirable, both rings and radials are intended to pass overcurrent for
short times because they're entirely capable of doing so, and it
significantly increases their utility.

As do Circuit Breakers. The point was, in the late 40's, British
manufacturing did not have the technology to make breakers at a
competitive price, so the fuse stayed as the main protection into the
80's, and is still the main protection for distribution boards.

so 5 seconds was standardied, hence the power companies
could continue to use their 100A fuses.

The pro voice was heard after dinner, and the vote taken that things
should stay as they are. When reading the minutes, it is pretty clear
that there is a good case for removing them,

Why dont you enlighten us, and we'll see.

A synopsis of it is he
http://www.google.co.uk/url?q=http:/...g/wiring-matte
rs/27/ring-circuit.cfm%3Ftype%3Dpdf&sa=U&ei=aiBaT5L-Os3m8QP9-pndDg&ved=0
CBkQFjAB&usg=AFQjCNG4mPYWY7FFtqVMluRlMzTm_o2_NQ

It gives the usual arguments. I was talking last week to an attendee of
that event, and he said the anti-rfc argument was far stronger, and
agreed by most people as sensible (they should not be used, apart from
specific applications) but dinner (or a break according to the
timetable) intervened, and it was agreed for no action, apart from the
ones at the bottom of the report.

The full report is available somewhere, though google has failed me.

Alan


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