replacing cartridge fuses with mcb's

[Iggifer]

Or here....
View attachment 90728
oops, lots of swear words edited out

thats a fancy programme...is it a newer version of XP

I'm gonna assume that's sarcasm....but if not  (although that may well just appear to most people as a square!)

 

[mrcrow]

Or here....
View attachment 90728
oops, lots of swear words edited out

thats a fancy programme...is it a newer version of XP

I'm gonna assume that's sarcasm....but if not  (although that may well just appear to most people as a square!)

dont we all gel wel..

 

[ban-all-sheds]

wikipedia will give correct spellings and the historical roots via latin, old english, greek, french and arabic
so you neednt be afraid of using...swive

It's not the correct spellings which concern me, it is the number of times the suggested alternatives for a misspelled word completely ignore the possibility that an adjacent key has been mistakenly struck and are very different to the "word" typed.

 

[ban-all-sheds]

thats a fancy programme...is it a newer version of XP

It does not have the look of XP.

 

[ericmark]

My understanding when changing from fuse to MCB is that with the fuse any slight error with loop impedance will make a similar slight difference in tripping time. However with a MCB if you exceed the impedance which is required to trip the magnetic part of the MCB it can make a huge difference in the tripping time. There is some debate as to if the line - neutral tripping time is so important however the line - earth is very important so unless there is a RCD to ensure it will trip with a line - earth fault the first job is to measure the earth loop impedance to ensure under fault conditions it will trip the magnetic part of the MCB.

So job one is measure the earth loop impedance before you consider changing them only if within the limits should you change. In theroy I know if a fuse is correctly selected then a MCB would replace it. But in practice many fuses were not correctly selected.

 

[mrcrow]

My understanding when changing from fuse to MCB is that with the fuse any slight error with loop impedance will make a similar slight difference in tripping time. However with a MCB if you exceed the impedance which is required to trip the magnetic part of the MCB it can make a huge difference in the tripping time. There is some debate as to if the line - neutral tripping time is so important however the line - earth is very important so unless there is a RCD to ensure it will trip with a line - earth fault the first job is to measure the earth loop impedance to ensure under fault conditions it will trip the magnetic part of the MCB.

So job one is measure the earth loop impedance before you consider changing them only if within the limits should you change. In theroy I know if a fuse is correctly selected then a MCB would replace it. But in practice many fuses were not correctly selected.

brilliant theroy old chap

 

[JohnW2]

brilliant theroy old chap

What eric wrote is essentially correct. IF a re-wireable (BS3036) fuse were correctly selected in relation to the earth loop impedance of the circuit then, in theory, I think that circuit generally ought to be more than acceptable for a Type B MCB of the same (or very similar) rating. However, as eric said/implied, in the days when re-wireable fuse CUs were installed, there is far from certainty that the appropriateness of the fuse rating to the EFLI would have been checked. Having said that, at least in my limited experience, it is pretty unusual for an 'ordinary' circuit in an 'ordinary house' not to have a low enough loop impedance for a Type B MCB.

Kind Regards, John