Possibly changing the 5 Second Disconnection Limit

Indeed, discussion is not normally a problem here, and is usually quite civilised, if sometimes terse,  though some err, "mission creep"  / " topic drift" is not unknown. ? 

I think we can all be guilty of forgetting the assumptions that underpin the way we do stuff, and seemingly 'basic' questions like 'why exactly 5 seconds ?' are often not at all easy to answer, comparisons to other places are often very interesting.

This does not mean we are going to suddenly change the mains voltage to 110v or anything, but it does not hurt to keep the door open to 'but what if ?' 

See you further down the log I hope.
LATE Edit

Looking at 250-122 (I do not normally look at 110V land regs so had to find a copy) it is the CPC size for various breaker ratings. This seems, unlike real cable ratings, to have current rating scaled linearly with area,

so 

6kA calls up 800 kcm ~ 450mm2

and 3kA calls up 400kcm  ~220mm2

1500A calls up 4/0 or about 120mm2

???

This makes ratings for lower currents a bit oversized - 30A (6mm2) or 20A (4mm ) look quite big to UK eyes

 This constant scale factor is not what we would do in the UK  - larger cables do not cool as well as small ones, (though they do have more thermal inertia so yo umay be OK for your long-ish breaking times),  and that on AC the current is not using the full cross-section.

Instead, the preferred approach where we have have no choice but to to throw around that many amps (and really we strongly prefer to get closer to the load at a higher voltage if possible, so high rise buildings may have HV LV transformers part way up) is to go for multiple bunches of thinner conductors in parallel, these would be  grouped into phase triplets 'trefoils'  or phase and neutral 'quarofoils' so the magnetic effects are somewhat cancelling.
    


Mike.

Indeed, discussion is not normally a problem here, and is usually quite civilised, if sometimes terse,  though some err, "mission creep"  / " topic drift" is not unknown. ? 

I think we can all be guilty of forgetting the assumptions that underpin the way we do stuff, and seemingly 'basic' questions like 'why exactly 5 seconds ?' are often not at all easy to answer, comparisons to other places are often very interesting.

This does not mean we are going to suddenly change the mains voltage to 110v or anything, but it does not hurt to keep the door open to 'but what if ?' 

See you further down the log I hope.
LATE Edit

Looking at 250-122 (I do not normally look at 110V land regs so had to find a copy) it is the CPC size for various breaker ratings. This seems, unlike real cable ratings, to have current rating scaled linearly with area,

so 

6kA calls up 800 kcm ~ 450mm2

and 3kA calls up 400kcm  ~220mm2

1500A calls up 4/0 or about 120mm2

???

This makes ratings for lower currents a bit oversized - 30A (6mm2) or 20A (4mm ) look quite big to UK eyes

 This constant scale factor is not what we would do in the UK  - larger cables do not cool as well as small ones, (though they do have more thermal inertia so yo umay be OK for your long-ish breaking times),  and that on AC the current is not using the full cross-section.

Instead, the preferred approach where we have have no choice but to to throw around that many amps (and really we strongly prefer to get closer to the load at a higher voltage if possible, so high rise buildings may have HV LV transformers part way up) is to go for multiple bunches of thinner conductors in parallel, these would be  grouped into phase triplets 'trefoils'  or phase and neutral 'quarofoils' so the magnetic effects are somewhat cancelling.
    


Mike.