This is why I am only using Hager due to the protools diagnostic app. Firmware updates available to improve the reliability of the devices. 

David.S does have his own unique style of presenting videos.  That may not be to everyone's taste but his content is sounds and his knowledge is good.   Many people have learnt a lot from his videos.  For example 4 or 5 years ago he was discussing should dual RCD CU be used in the domestic areana.  He heighlights points like troubleshooting, Nuisance tripping,  Diversity, Earth fault leakage from LED and such other electronics.  He has started many a discussion in the electrical community.  Now a days most people fit a minimum full RCBO cu but back then people fitted Dual split load RCD.   Unfortunately some electricians are still fitting dual split load RCD as they have to follow the design from the main contractor.  I went to a Taylor Wimpey flat recently,  finished only 6 months ago and it has a Dual RCD board.  Personally I think dual Split load RCD CU were never compliant.  That can gone back to probably the 16th Edition of BS7671

I wouldn't be so quick to judge. He raises some valid points. I would also take some time to read through the comments posted below the video, there some well-informed minds commenting there amongst the usual dross.

Interesting to note the type testing requirements from the AFDD Standard. What this appears to mean is that it is not possible to construct a MFT type AFDD test function due to the amount of energy dissipated during the test.

Also, for those who think that an appliance arc fault would be picked up, for example the grenfell fridge - a AFDD would not have detected it.

What this appears to mean is that it is not possible to construct a MFT type AFDD test function due to the amount of energy dissipated during the test.

I read that comment too, and found it a very unlikely excuse, or the quoted energies are off by miles..

It is quite practical to dissipate one or two  kJ into a few cubic inches of metal box and then let it out slowly. There may need to be be quite a long interval between re-tests of course, but that is a reasonably limitation. ( e.g. you permit a 1kJ  strike every minute, that  is a mean dissipation of just under 17 watts continuous equivalent - a level like that can be quite easily hand held.)

A common approach is to allow material phase changes, such as melting and re-solidifying wax, within your metal block, as then you can even absorb heat with negligable rise in temperature above some limit near the melting point, in much the same way as water stays cool until all the ice has melted or boiling water does not get much above 100C until all the liquid has become gas.

Mike

Certainly worrying that an AFDD can be "dead" out of the box, and the issue not be detectable on-site.

I didn't quite follow the Grenfell fridge comment though - the last time I took a fridge apart (which was a long time ago admittedly) the one thing it didn't have was an isolating transformer - all the major components (compressor motor, light, edge heater, thermostats) were all directly connected as I recall. Maybe "smart" ones these days are all driven by electronics? (or maybe the electronics just drives a relay that controls the motor?)

Maybe an AFDD wouldn't have seen the fault anyway (an overheating compressor motor I would imaging be closer to resistive heating than arcing until it was too late anyway), but I'd still like to understand the thinking behind the comment.

        - Andy.

Hi Andy

whjohnson said:

Also, for those who think that an appliance arc fault would be picked up, for example the grenfell fridge - a AFDD would not have detected it.

I think that comment was by whjohnson

It would be good to hear his thought process on this. 

AJJewsbury said:

Certainly worrying that an AFDD can be "dead" out of the box, and the issue not be detectable on-site.

That would be a question for the R&D Team at Hagar to investigate.  Maybe they are unaware that the AFDD POST (Power On Self Test) does not detect certain issues and then fails safe.  It would be interesting to get some imput from Hagar on this.

What aspect of a fridge catching fire do we think an AFDD would detect that say an MCB or RCD would not ?
Certianly if there was not much else switched on even a classic arc signature would be ignored - AFDDs have to be made to ignore arc-like waveforms of less than a few amps to avoid tripping on normal operation of brushed motors.

By the look of the forensic evidence of dr-j-duncan-glovers-expert-report  in interview he seems to reckon that a poor crimp inside a hot point Fridge freezer caused the insulation to overheat and then burn.

"A probable cause of the fire is a poor crimp connection for... an overheated wire connector within the compressor relay compartment for the fridge-freezer (Hotpoint Model FF175BP) from Flat 16."

.....

 "The overheating connector in my opinion was the first event that started burning the insulation on the wires that led to a short circuit."

..... 

"The overheating of the crimp starts the fire. It overheats, it glows, it ignites."

 (transcript of that verbal evidence here ) Pages 60 to 85 are most relevant.

Equally in his actual  written report he also mentiones

" Conversely, the following observations do not support a fire origin within BPS/I,
the fridge freezer from Flat 16.
(1) No arc damage was observed within BPS11.
(2) The 13A fuse for the fridge freezer power supply cord is intactinot blown.
(3) Whirlpool has reported that there have been no recalls and no legal
proceedings/claims against Whirlpool, Trulesit, Or its representatives involving
a. Hotpoint FF175BP or FF175B G."

But given the charred mess remaining, it would be a brave soul who concluded much at all without some sort of caveats. Note that the no 7 'kitchen' breaker had tripped at least by the fire had taken hold, while other circuits did not, and the owner turning off the main switch as he escaped in many ways helped to preserve the scene as nothing else was tripped later due to cable burning through.

Mike.

mapj1 said:

led to a short circuit

Excuse my ignorance in this but.  Was the short L to N or L to E or is the power in

Hotpoint Model FF175BP)

Direct Current. 

Are AC and DC arc the same same signature?  My understanding is that DC can jump arc or spark further distances than AC

mapj1 said:

(2) The 13A fuse for the fridge freezer power supply cord is intactinot blown.

13 amp seems a bit high for a fridge

I am afraid that I  do not know about anything relating to Grenfall for sure any more over and above that in the evidence publically available, that I have linked to above - if you have more please share.

I think my fridge has a 13A fuse - the inrush is quite fierce - 80-100 amps for the first cycle or so, I suspect others are similar, and a 5A one may die after a few starts.

M.

A DC arc does not self extinguish at the zero crossing like AC but the ca[ability to draw an arc length is comparable if enough current is available to feed the ionisation of the plasma. In practice DC swithches need larger gaps and a much faster rate of separation for the same voltage. The fridge freezer will be mains though.

I am afraid that I  do not know about anything relating to Grenfall for sure any more over and above that in the evidence publically available, that I have linked to above - if you have more please share.

I think my fridge has a 13A fuse - the inrush is quite fierce - 80-100 amps for the first cycle or so, I suspect others are similar, and a 5A one may die after a few starts.

M.

A DC arc does not self extinguish at the zero crossing like AC but the ca[ability to draw an arc length is comparable if enough current is available to feed the ionisation of the plasma. In practice DC swithches need larger gaps and a much faster rate of separation for the same voltage. The fridge freezer will be mains though.

Not sure I'd even be as confident as he was looking at that to be honest.

But he did do some CT scans of crimps and found serious voids.