re grenfell tower fire question

[ss]

Not being electrically savvy but should the `trip` switch on the mains meter not have clicked in and cut the current off to prevent a fir starting.

[tabbypurr]

Depends on the details of the fridge fault. MCBs certainly don't eliminate all fires.

NT

[Tim Watts]

What trip switch?

[NY]

The over-current or earth leakage trip-switches in the "fuse box". Or in extreme case the 60 A "company fuse" (which i think is always still an old-fashioned melting-metal fuse). But I think you *did* know that.

The difficulty is when the short is not to earth and is a lower-than-normal resistance but not a complete short, so you draw a larger current (or a current through the wrong material, allowing it to heat up) but not a current that is large enough to blow/trip the cutout.

[Tim Watts]

It sounded to me like the PP thought there was some magic fire detecting device...

Back to the point, the fuse in the fridge's plug would be the first to go, unless there was an RCD *and* the appliance is a Class I (earthed) device (which seems likely for a metal fridge).

But it's possible to start a fire with no serious overload - with the right conditions, an amp at 230V can make things extremely hot - and if the hot thing is next to a combustible thing...

[John Rumm]

Not necessarily - it depends on if the fault caused it to draw too much current or allow excess earth leakage. If the answer to both those is "no", then the circuit protection will be none the wiser that things are going pear shaped elsewhere.

[tabbypurr]

The bimetal cutout on the fridge compressor, the plug fuse, the MCB, the RCD, the supplier's fuse and if present (very unlikely) an AFCI are all fire preventing devices. All of them only work on a percentage of fire causing faults.

NT

[Graham.]

I've never seen an AFCI, I see they are now common in the USA and that they are prone to false tripping.

[tabbypurr]

AIUI the 18th will make them common here. A workaround will be needed for old arcy sparky equipment.

NT

[Martin Brown]

ELCB may potentially save you if the cable chars or melts sufficiently to allow a live to earth current that trips it out. But if you are out of luck the leak goes live to neutral and a nominal 13A fuse will support something like 20A for a few minutes...

Seen that happen with internally molten overloaded extension leads that haven't been unwound properly. All the ones in out village hall now have thermal cutouts to defend against potential abuse.

It is particularly bad in those tall floor fan heaters that swivel from side to side with a 13A fuse and a cable that is forever being twisted to and fro when the thing is in use and allowed to move as designed.

It isn't really a case of if it fails so much as when...

[Brian Reay]

While, assuming there was an RCD on the circuit, it is hard to believe once the fire 'took hold', the insulation wouldn't cause it to trip, the fire could easily continue to burn.

The real question is, why the occupier/owner didn't take steps to contain the fire and call the fire brigade. Early reports indicate he collected items and told a neighbour, who could see the fire in his kitchen- meaning the door to his flat was open. Had the precaution of simply closing doors and windows etc. and ensuring the fire service were called, could the fire have been contained?

Those being evacuated in Camden reported that there had been several fires in their block(s), all of which had been contained.

This isn't an attempt to blame the tenant, he may well have simply panicked or not known what to do for whatever reason. Sadly, such things happen.

[Jim GM4DHJ ...]

when the transformer went in my TS520SE the amount of smoke was unbelievable but I managed to cut the power before the house RCD tripped .......

[Andrew]

I blame 'frost-free' fridge freezers. This involves heating elements in close contact with plastic and nasty insulation, and circuit boards with microprocssors that then need a low voltage dc supply from the mains, which means additional gubbins that can overheat.

My Liebherr fridge freezer has a bog standard electro-mechanical thstat with wax inside it and the microswitches are enclosed inside a fairly tough metal box.

[Davey]

Your what?

[Jim GM4DHJ ...]

yes that ....

[Johnny B Good]

For the benefit of those who lack basic google skills (or CBA to google), it's a 1970s Kenwood "Ham Radio" shortwave transciever designed to be run off mains power (120/220/240vac). Presumably he meant the mains transformer in the integrated supply which, in this case would have been a special to provide heater and HT voltages for the valves (vacuum tubes) as well as low level DC voltages for the transistorised portions (it was a 'Hybrid' design relying on valves in the final stages of the transmitter to achieve its 100W PEP RF output power rating).

[Davey]

Thank you. It would have been simple to include a reference to its purpose in the original message, such as:

"when the transformer went in my TS520SE shortwave transceiver, ... . "

[Johnny B Good]

[Jim GM4DHJ ...]

jeeezus christ I was replying to another albeit class B radio ham Brian Reay...

[Bob Eager]

No such thing as a class B.