breaking capacity of fuse and mcb

[Des 56]

The way I understand
If the board is domestic and not exceeding 100 amp the board is covered by the suppliers fuse, the breaking capacity of the mcbs doesn't have to be greater than the PFC
Over 100 amps or non domestic the above wont apply

 

[tony mc]

This subject has been raised a few times and I brought it up at one of the Elex Q & A sessions for that reason.

Its my beleif that the type testing on the CU is up to 16 kA.

Have a look at 530.3.4 .

And that was also the agreed answer from the panel at the Elecx show.

 

[Guest55]

Have a look at 530.3.4 .

just read it twice , says absolutely nothing to suggest mcb ratings are anything other than whats stamped on them.
the reference to bs no is the standardised assemblies for CU's.

 

[Guest55]

The way I understand
If the board is domestic and not exceeding 100 amp the board is covered by the suppliers fuse, the breaking capacity of the mcbs doesn't have to be greater than the PFC
Over 100 amps or non domestic the above wont apply

fuse size is irrelevent , the pfc is decided by how close the service is to the dno transformer - so even if your cut-out fuse is only 60A your pfc could be as high as 4Ka if youre 400 yrds from a local substation.
if you put 2ka fault through a 1ka mcb - it will operate but cease to work correctly from thence.
in essence , youre choosing a device that will be destroyed after tripping.

 

[Des 56]

here is a link to some information that may assist
http://www.google.co.uk/url?sa=t&rc...yICwAg&usg=AFQjCNFlUne8kh7xdY1-oCcv2xrC7S_4fA

 

[Engineer54]

fuse size is irrelevent , the pfc is decided by how close the service is to the dno transformer - so even if your cut-out fuse is only 60A your pfc could be as high as 4Ka if youre 400 yrds from a local substation.
if you put 2ka fault through a 1ka mcb - it will operate but cease to work correctly from thence.
in essence , youre choosing a device that will be destroyed after tripping.

And why the manufactures produce 25KA MCB's. eg, ...For use in final circuit installations very close to the distribution transformer as would be found in a sub-station house/building...

 

[lauriehurman]

Is the 1kA Is or In ? I can never remember.

Also you can upgrade to 16kA 1361s very easily with the little plastic Wylex converter thingy (don't know real name but TLC get them for me).

Laurie

 

[telectrix]

In is the tripping current. e.g. 6A,16A,32A, Isc is the short circuit current .

 

[tony mc]

just read it twice , says absolutely nothing to suggest mcb ratings are anything other than whats stamped on them.
the reference to bs no is the standardised assemblies for CU's.

Like I said before this issue has raised its head a few times.

GN 3 explains it a bit better than the regs on page 57 .

The BS EN 60439 bit refers to Annex ZA but I can't seem to find that.