Unfused spur.

The 1.5mm2 6242Y is no longer than 300mm and runs through a brick wall. It starts from a deeply sunk double metal box and terminates at a surface mounted all insulated 13 Amp. I.P. 64 rated single 13 Amp socket. Any physical damage is very unlikely.

It's not just about physical damage - faults can occur from many causes. I'm sure we've all come across back boxes where a wire has come loose and touched something it shouldn't or been nicked by one of the faceplate fixing screws (possibly after Mr DIYer has been loosening faceplates to redecorate or otherwise messing with things).


You might have been thinking of omitting fault protection (3m and all that - 434.2.1) - but I'd be uncomfortable with that personally - squashing things into a back box isn't really in the sprit of (ii) to my mind.

 

The energy let through you are quoting is at the DB with 6kA PSCC (or 3kA) ....  The other points to consider are the PSCC at the point the 1.0 Earth conductor joins, which will not be 6kA or even 3kA, it might be as high as 575A if the ring is short and the DB PSSC high. The by the book calculation is not a theoretical possible maximum value, it is an actual value.

Agreed - but does that help? Lets say the actual fault current was say 600A - what we'd then need to know is how long the MCB takes to open at that current (it could well be slower than for a 3kA fault) - but we don't have that data. The time-current curves don't go above 160A for a B32 and the regs send us back to using energy let-through data - which again normally isn't supplied for 600A. All we know is that it shouldn't be longer than 0.1s - but that's far too long to be useful. BS EN 60898 just gives us a single table of energy let-though data (based on the device's rating rather than the actual fault current) - so we're back to 18,000 A²s again. If Z. had told us the manufacturer of the MCB we could use manufacturer's data rather than generic BS EN 60898 data  - which may or may not give us some more favourable figures (but often they're just reproductions of the BS EN 60898 ones anyway).


Z. asked if it complied - I still say we can't say that it does. It may well be probably OK or unlikely to be an issue in reality, but probablys and unlikelys don't show compliance.  Maybe Z. can provide some more data so we can be certain, but I don't think we're there yet.


   - Andy.

The 1.5mm2 6242Y is no longer than 300mm and runs through a brick wall. It starts from a deeply sunk double metal box and terminates at a surface mounted all insulated 13 Amp. I.P. 64 rated single 13 Amp socket. Any physical damage is very unlikely.

It's not just about physical damage - faults can occur from many causes. I'm sure we've all come across back boxes where a wire has come loose and touched something it shouldn't or been nicked by one of the faceplate fixing screws (possibly after Mr DIYer has been loosening faceplates to redecorate or otherwise messing with things).


You might have been thinking of omitting fault protection (3m and all that - 434.2.1) - but I'd be uncomfortable with that personally - squashing things into a back box isn't really in the sprit of (ii) to my mind.

 

The energy let through you are quoting is at the DB with 6kA PSCC (or 3kA) ....  The other points to consider are the PSCC at the point the 1.0 Earth conductor joins, which will not be 6kA or even 3kA, it might be as high as 575A if the ring is short and the DB PSSC high. The by the book calculation is not a theoretical possible maximum value, it is an actual value.

Agreed - but does that help? Lets say the actual fault current was say 600A - what we'd then need to know is how long the MCB takes to open at that current (it could well be slower than for a 3kA fault) - but we don't have that data. The time-current curves don't go above 160A for a B32 and the regs send us back to using energy let-through data - which again normally isn't supplied for 600A. All we know is that it shouldn't be longer than 0.1s - but that's far too long to be useful. BS EN 60898 just gives us a single table of energy let-though data (based on the device's rating rather than the actual fault current) - so we're back to 18,000 A²s again. If Z. had told us the manufacturer of the MCB we could use manufacturer's data rather than generic BS EN 60898 data  - which may or may not give us some more favourable figures (but often they're just reproductions of the BS EN 60898 ones anyway).


Z. asked if it complied - I still say we can't say that it does. It may well be probably OK or unlikely to be an issue in reality, but probablys and unlikelys don't show compliance.  Maybe Z. can provide some more data so we can be certain, but I don't think we're there yet.


   - Andy.