Main switch short circuit capacity.

Actually having checked, OMS's answer is (of course, silly me, why do I check?) the one you want. I am indeed doing as I usually do, when I do anything I don't do very often without the text book in front of me, and dropping random factors of root two, pi, -1 etc.


The line that is not a fuse line, and slopes up steeper, is to allow us to convert  between pk-pk and  RMS values (in the ratio of 1RMS = 2.5 and a bit  pk-pk) , and this line too needs to be extended to allow you to convert what a REC 4 could stand back to RMS again. (This is useful because at short breaking times the waveform is not really a steady state sine wave, being much less than a cycle long, so a single sided pulse with some ringing but we need an RMS equivalent to estimate the heating. )

It does not alter the conclusions, luckily for us, that the the REC 4 is fine on any supply you can safely protect with a  100A BS1361: 1971 fuse, just the margin of safety is rather greater than I first said, by about 2.5 to 1.. (I did warn you it would rely a bit on other people checking my workings ? )

Actually this means you could probably use 6kA MCBs after the fuse and REC4 arrangement if you wanted to.

As an aside the NOZED and DIAZED bottle fuses are used on the continent as incomer fuses to have similar dramatic damage limiting effects see this data sheet  here on  page 4 and nearby  The 'death or glory' fuse may be old hat but it is jolly handy thing to remember. Also why bypassing them with bits of coathanger wire can be such a bad idea.

Actually having checked, OMS's answer is (of course, silly me, why do I check?) the one you want. I am indeed doing as I usually do, when I do anything I don't do very often without the text book in front of me, and dropping random factors of root two, pi, -1 etc.


The line that is not a fuse line, and slopes up steeper, is to allow us to convert  between pk-pk and  RMS values (in the ratio of 1RMS = 2.5 and a bit  pk-pk) , and this line too needs to be extended to allow you to convert what a REC 4 could stand back to RMS again. (This is useful because at short breaking times the waveform is not really a steady state sine wave, being much less than a cycle long, so a single sided pulse with some ringing but we need an RMS equivalent to estimate the heating. )

It does not alter the conclusions, luckily for us, that the the REC 4 is fine on any supply you can safely protect with a  100A BS1361: 1971 fuse, just the margin of safety is rather greater than I first said, by about 2.5 to 1.. (I did warn you it would rely a bit on other people checking my workings ? )

Actually this means you could probably use 6kA MCBs after the fuse and REC4 arrangement if you wanted to.

As an aside the NOZED and DIAZED bottle fuses are used on the continent as incomer fuses to have similar dramatic damage limiting effects see this data sheet  here on  page 4 and nearby  The 'death or glory' fuse may be old hat but it is jolly handy thing to remember. Also why bypassing them with bits of coathanger wire can be such a bad idea.