breaking capacity of fuse and mcb

[goldie]

Cant seem to find info anywhere for bs3871 m1 plug in wylex type b mcb. Anybody know the braking capacity??
also wylex 5a fuse wire pls
Merry christmas

 

[Des 56]

Put this into google (wiring matters 29 semi enclosed fuses )and click on the IET link that comes up
It's quicker than me writing them out

 

[goldie]

Yo. good man. Ta

 

[telectrix]

BS3871 MCB... M1=1ka. M1.5=1.5ka. M3=3ka. etc...

 

[Guest55]

Tels quick on the draw tonite - must be the mince pies and sherry lol.

 

[goldie]

Cheers tel. M1 is the one i was looking for.

1ka!!??? pretty low. i guess the main incoming service fuse should cover it if pfc is high.

 

[tony mc]

He is!

I had a look at that wireing matters 29 and could not see anything about 3871 mcb;s or is it me !

 

[goldie]

He is!

I had a look at that wireing matters 29 and could not see anything about 3871 mcb;s or is it me !

same here. Only got the 3036 fuses. Maybe its because they are superseeded?

 

[Guest55]

Cheers tel. M1 is the one i was looking for.

1ka!!??? pretty low. i guess the main incoming service fuse should cover it if pfc is high.

no it wont sadly , mcb breaking capacity must match pfc at the CU's terminals.

 

[Des 56]

He is!

I had a look at that wiring matters 29 and could not see anything about 3871 mcb;s or is it me !

me neither,what a silly link :26:


(also wylex 5a fuse wire pls)

 

[goldie]

Al jst pop a new dist board in then biff

 

[tony mc]

I think you will find if the CU meets EN BS 60439 the CU is rated up to 16 kA as a whole irrespective of the individual componants which vary in domestic boards !

 

[Guest55]

I think you will find if the CU meets EN BS 60439 the CU is rated up to 16 kA as a whole irrespective of the individual componants which vary in domestic boards !

that only applies to the internal bus bars , terminals and links within the CU , it does not extend to mcb's which are rated seperately.

 

[goldie]

I think you will find if the CU meets EN BS 60439 the CU is rated up to 16 kA as a whole irrespective of the individual componants which vary in domestic boards !

thats what i always thought. Till biff pi###d on my bonfire.
Got a 100a 1361 type 2 b (33ka)

 

[Guest55]

thats what i always thought. Till biff pi###d on my bonfire.
Got a 100a 1361 type 2 b (33ka)

if all mcb's were automatically rated to 16 ka when fitted in a CU why would they all have 2 , 4 , 6 , 10 Ka stamped on the side ?

 

[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.