I don't think that I have ever felt a hot BS 1363 plug

I've come across a few. Seemingly a few EV owners with granny leads have too. I suspect in some cases at least it's a combination of events - heat from the fuse warms the socket contact springs,which means they gradually loose their temper, which results in a poor connection, with increased resistance, and so more heat. Probably not helped with the move away from pretty substantial thermosetting (urea formaldehyde?) plugs with solid brass pins to thermoplastic moulded ones with reduced c.s.a pins to allow for pin sleeving. Less mass to absorb the heat, probably less thermally conductive housing and lower surface area for heat to escape from, combined with a plastic that deforms more when warmed.

   - Andy.

I have managed to burn myself quite badly on the pin tips of a 13A plug that had been overloaded for several minutes, but it was not in good shape, the brass being quite dull. It was  an older rubber backed kind and I did wonder if the rubber had exuded something nasty that caused the tarnishing to be particularly bad. Even so  I was a bit surprised, and more generally my experience is that when they fail it is indeed the live pin that gets it worst, presumably due to the overheating caused by the fuse itself, and that is a handful of times over as long as I can remember

And on one case the plug had welded into the socket, and both had to be removed as an item - oddly on a tumble dryer of ~ 8A rating, but in a relatively damp laundry room, and had been heavily worked.

machine a piece of brass rod Note, but do not copy!.. Some designs of 13A plug can be dismantled in a way that two can be made into one with a pair of neutral pins and no fuse. Again not right and a source of alarm to all who find it later....

More generally the dissipation within the 13A plug is not something that is as well handled as in the old BS4343 /IEC 60309 styles , which  are  much more generous with the volume of metal available  for heat dissipation and the ability to handle over load.

(perhaps a smaller fuse, as in a shorter lower resistance element of the same 13 A Rating would have been better. The 6kA survival requirement might have been harder to meet though.)

Mike

Follow-on question: If I've got a fixed 230:110V transformer feeding a 16A tool socket, am I right in thinking the MCB feeding the transformer will need to be rated at about 8A? 

yes, transformer action means that as voltage rises by the turns ratio the current falls. but actually, you will want rather more than that to handle the inrush. so it may need to be C or even D type ane probably 10 amps or more.
Mike.

Follow-on question: If I've got a fixed 230:110V transformer feeding a 16A tool socket, am I right in thinking the MCB feeding the transformer will need to be rated at about 8A? 

Well the transformer should draw around 8A steady state at 230V ... but an MCB of that rating would be problematic ... partly because they don't make 8A MCBs but mostly because steady-state is only happens once things have settled down. Most appliances draw rather more than their rated current when they start up (filament lamps and heaters have a lower resistance when cold, motors need extra power to accelerate to their working speed, capacitors need current to charge if switched on when the a.c. cycle isn't at zero, likewise inductors). That's why you'd often see 13A fuses supplied with fridges/freezers even though they're only rated at a couple of hundred watts. It's not that protective devices open instantly the moment the current exceeds their rating even by a fraction - but there is a trade-off between the size of the overload and the time the protective device will remain operational. Small overload will take some time to trip, but very large currents will open it much more quicky.   Transformers have especially large starting currents as they establish their magnetic fields (plus any starting currents from downstream loads if they happen to be connected) often many many times their running current, so can easily trip circuit breakers rated for only the running current. With MCBs some compensation can be had by selecting a higher "type" - e.g. D type rather than B or C, but still some care is needed to co-ordinate things properly.

More generally, there's usually little need to tie the rating of protective device too tightly to the size of the load. The protective device is mostly there to protect the conductors feeding the appliance, rather than the appliance itself (unless the manufacturer specifies otherwise). For instance a 16A MCB feeding 20A cables feeding a 1A load is usually perfectly fine.

   - Andy.

AJJewsbury said:

they don't make 8A MCBs

FWIW, Eaton do.

https://datasheet.eaton.com/datasheet.php?model=EMBH108&locale=en_GB

FWIW, Eaton do.

Blimey, so they do. Every day a school day!

   -Andy.