Quick AFDD question

[pgtips]

Hi,
Helpful members recently guided me to AFDD rcbo.
Arc Fault Detection Device.

Different AFDD on the market, 32a, 10a, 6a and others for the circuits, I'm slowly accumulating but my question is should the main 63A also be an AFDD ?

Thank you

 

[Murdochcat]

Where do think it’s necessary to fit these awful devices ?

 

[flameport]

I'm slowly accumulating but my question is should the main 63A also be an AFDD ?

No.
One AFDD = one circuit.

 

[pgtips]

Where do think it’s necessary to fit these awful devices ?

It's peace of mind, a step forward, call it what you will but I'd rather have extra protection than less. Yes expensive but I'd never forgive myself if something happened.

I've only recently become aware of them but they do seem to polarise opinion but makes no sense. What's negative about safer!

Probably a bit paranoid but I've also just bought a PAT as well. (a primetest 50)
Pg

 

[AndyPRK]

I don't think they work on ring circuits, so don't bother buying too many 32A ones.

Hagar ones don't seam to trip very well.

 

[ebee]

I reckon that a lot of us (including a lot of professional electricians and electrical engineers) regard them as probably “snake oil” at best , we have yet to be convinced of any tangible benefit at any price and not worthy of consideration.

I would rank them lower down in priority than Surge Protection Devices ( which probably are beneficial to the point I would put them in new installations but I’d not panic to put them in existing installations unless I suspected a possible beneficial reason for that particular installation).

I hope that helps

 

[Jurassicspark]

I don't think they work on ring circuits, so don't bother buying too many 32A ones.

They do work with ring circuits. They are just unable to detect a series arc in line or neutral.

All arcs in spurs & connected devices and parallel arcs in the ring are detected.

 

[Jurassicspark]

question is should the main 63A also be an AFDD ?

No.

That would cause nuisance tripping. Something similar I've seen before with multiple circuits with too much noise on them especially somewhere on site which means the AFD has to decide what is an arcing fault and what isn't, take your vacuum motor or fridge, it needs to know the arcing on the brushes is not a fault.

 

[JohnW2]

All arcs in spurs & connected devices and parallel arcs in the ring are detected.

That "all" presumably requires qualification, given that you have recently reported a case of arcing, with things getting "mad hot" in which the AFDD did not operate?

 

[JohnW2]

I reckon that a lot of us (including a lot of professional electricians and electrical engineers) regard them as probably “snake oil” at best , we have yet to be convinced of any tangible benefit at any price and not worthy of consideration.

As you know, I'm not one of those people but, for what it's worth, on the basis of what I so far know, I certain subscribe to that view. Having said that, there are clearly also some professional electricians who are advocating them.

At least as far as domestic installations are concerned (and,again, for what it's worth) I personally strongly suspect that this is the case of a 'solution' which has appeared because it has become technologically possible (and which affords a means of much money-making by manufacturers), but a 'solution' to a very questionable 'problem'.

I would rank them lower down in priority than Surge Protection Devices ....

I would certainly agree with that, but ....

.... ( which probably are beneficial to the point I would put them in new installations but I’d not panic to put them in existing installations unless I suspected a possible beneficial reason for that particular installation).

As you are aware, I'm pretty sceptical about them, too (again because I question the magnitude of the 'need', hence 'cot/benefit) - and (unless one really scrapes barrels), they are not even related to 'personal safety'.

 

[Jurassicspark]

That "all" presumably requires qualification, given that you have recently reported a case of arcing, with things getting "mad hot" in which the AFDD did not operate?

I have NO doubt AFDDs work for the specification they have been made to meet, and that specification goes into great depth about when, and how, it should trip. But given others have tried to replicate 'real world' situations and struggled to trip the AFDDs I think we need a demo that is genuinely more 'real' to show that they work in the real world and will save lives.

And sometimes AFD's trip without a valid reason so...?

 

[JohnW2]

I have NO doubt AFDDs work for the specification they have been made to meet, and that specification goes into great depth about when, and how, it should trip.

I'm sure that's right but, as you go on to say/imply, that is little/no consolation, and really 'little use', if, despite that, the devices fail to operate in 'real world' situations.

And sometimes AFD's trip without a valid reason so...?

Indeed -just as with 'nuisance trips' of RCDs (albeit I have personally experienced extremely few of them). So, we have the 'risks'of freezer contents being lost, people being 'plunged into darkness' (and falling off ladders or down stairs, or dropping pans of boiling oil) etc.

Although it's a case of 'who am I to have an opinion?', if those 'risks' (in addition to similar ones presented by RCDs) are not adequately balanced by 'benefits', then I would personally be inclined to regard the devices as 'bad news' ('detrimental to safety').

 

[pgtips]

thank you to everyone for the replies. makes perfect sense that it would be a nuisance (if it was AFDD on the main 63) , I just hadn't thought it through that way so thank you again.

 

[JohnW2]

thank you to everyone for the replies. makes perfect sense that it would be a nuisance (if it was AFDD on the main 63) , I just hadn't thought it through that way so thank you again.

As you will have seen, opinions about these devices vary, and some may well feel that they could have some 'nuisance value' even when used to protect individual final circuits.

 

[Jurassicspark]

Although it's a case of 'who am I to have an opinion?', if those 'risks' (in addition to similar ones presented by RCDs) are not adequately balanced by 'benefits', then I would personally be inclined to regard the devices as 'bad news' ('detrimental to safety').

If its a domestic property then someone can say to the customer, "I wouldn't recommend AFDD in this case as the property is not in the high-risk category and the high cost of AFDD at this time is difficult to justify. Other steps to reduce the risk or impact of fire, such as a full linked fire alarm and/or some extinguishers would bring greater benefit.".