Saturday Night Discrimination Quiz/Guess

[EFLImpudence]

Last go, tfb.

Only the 5A fuse should have blown @ 30A in 0.1s.
So, nothing else should have happened - but did.

5A fuse, 16A RCBO and 32A MCB because of overcurrent then Active RCD socket.

 

[PrenticeBoyofDerry]

O come on! was it not me that mention 32A first and then led on to RCD at plug socket?
Medal, medal, medal.......

 

[echoes]

Is there a small period of time where an MCB is in the process of tripping,
but has not yet gone open-circuit, during which time the 5A had time to melt?

 

[echoes]

O come on! was it not me that mention 32A first and then led on to RCD at plug socket?
Medal, medal, medal.......

I agree!

 

[PrenticeBoyofDerry]

you could also factor in the age and condition of the devices.

 

[EFLImpudence]

Is there a small period of time where an MCB is in the process of tripping,
but has not yet gone open-circuit, during which time the 5A had time to melt?

Other way round.

5A should blow 'instantly' at 30A.

 

[EFLImpudence]

O come on! was it not me that mention 32A first and then led on to RCD at plug socket?
Medal, medal, medal.......

I agree!

Me, too.

 

[JohnW2]

O come on! was it not me that mention 32A first and then led on to RCD at plug socket? Medal, medal, medal.......

Consolation medal, perhaps You were, indeed, the first to mention the 32A MCB, and also the first to mention the active RCD - but even when I indicated that you were looking for a third device, you never suggested 32A MCB + 5A Fuse

Kind Regards, John

 

[PrenticeBoyofDerry]

I hate them 5A fuses

 

[JohnW2]

Is there a small period of time where an MCB is in the process of tripping,
but has not yet gone open-circuit, during which time the 5A had time to melt?

Other way round. 5A should blow 'instantly' at 30A.

The problem with all the operating curves I've seen is that they stop at 0.1 second. I therefore don't know how one can really be sure of the relative (sub 0.1 sec) operating times of, say, a B32 MCB and a 5A BS 1362 fuse in the face of a very high current.

Kind Regards, John

 

[JohnW2]

Is there a small period of time where an MCB is in the process of tripping, but has not yet gone open-circuit, during which time the 5A had time to melt?

I wouldn't give up on that idea as readily as you seem to have done. I'm not sure why EFLI is talking about 30A (at which current a 5A fuse should blow 'instantly' {>0.1 SEC}, but a B32 would obviously not even have started thinking about operating). At a current of a few hundred amps (which is more like what one would expect of an L-N fault), the B32 would also operate 'instantly' (<0.1sec) - the question then being which one operates 'more instantly' than the other (per my recent post regarding the operating curves).

There presumably inevitably will be, as you suggest, a very brief period after an MCB has got beyond the 'point of no return' before disconnection actually occurs. Similarly, a fuse presumably can get 'beyond the point of no return' in terms of melting such that the melting will 'complete' even if current flow ceases.

Kind Regards, John

 

[ban-all-sheds]

It's usually my trick, but this afternoon it was my neighbour's turn to 'hedge cut' the cable of his hedge cutter! He totally sliced the two core cable supplying the Class 2 tool, without any contact with the nearby earth.

At this time of night I so can't be rsed to read 4 pages.

Nothing personal, and apologies if this is superfluous, but that example is why I believe that 3-core flex should be used for Class II appliances like that.

 

[JohnW2]

you could also factor in the age and condition of the devices.

It would great to be able to 'factor in' such consdierations but, beyond knowing that these are going to be relevant factors in determining 'what happens', I don't think one is ever going to have enough information/data to be able to draw any conclusions from such 'factoring'.

... which brings me back to one of my pet topics - that (unlike the situation with RCDs) we don't really seem to have a clue about the in-service 'failure' rate of MCBs, or of any in-service changes in functional characteristics of MCBs over time. I just can't help wondering how many (or how many millions of!) MCBs there are in service which would not operate as expected (or at all) when needed 'in anger'.

Kind Regards, John

 

[JohnW2]

Last go, tfb. .... 5A fuse, 16A RCBO and 32A MCB because of overcurrent then Active RCD socket.

Almost - just one too many! I guess that deserves a prize, too (and I'll assume that you hadn't seen the answer before you pressed the 'submit' button ).

Kind Regards, John

 

[JohnW2]

At this time of night I so can't be rsed to read 4 pages. Nothing personal, and apologies if this is superfluous, but that example is why I believe that 3-core flex should be used for Class II appliances like that.

Well, it's superfluous to the game/discussion we've been having, and superfluous to the incident which happened (since 'instant' disconnection occurred, even with 2-core flex) but, FWIW, I'm very much inclined to agree with you.

Kind Regards, John