Strangely we do have evidence from the USA which has mandated AFDDs for 13 years. It may be because of poor fire investigation but there is no statistically significant difference between fire rates 13 years ago and now, although one would expect the to be. Another point is that AFDDs in the USA are very significantly cheaper than here, and also Germany which has had them for several years has no statistics. This is all very curious, as allegedly they are useful to prevent fires. If they are useful for appliances then they should obviously be incorporated in those! I think Andy is on the right lines here. (Personal opinion BTW, just to be clear).

I will repeat my point, the product standard test is not real and is useless, unlike the RCD test which has stood the test of time and is much more like real situations.

David Stone said:

Strangely we do have evidence from the USA which has mandated AFDDs for 13 years. It may be because of poor fire investigation but there is no statistically significant difference between fire rates 13 years ago and now, although one would expect the to be.

Only if a significant number of electrical installations (compared with the initial number of electrical installations > 13 years ago) had been either newly installed, or refurbished to the relevant codes in force at the time.

David Stone said:

Another point is that AFDDs in the USA are very significantly cheaper than here, and also Germany which has had them for several years has no statistics. This is all very curious, as allegedly they are useful to prevent fires.

Well, I can see why one would make that point.

But to counter it, I must ask are there any statistics on exactly how many lives have been actually saved with RCDs? Probably not, and I don't think anyone would even bother commissioning a research study, because we really don't need that to make the decision whether to use them ... at least  in 2022; compare, however, with 'back in the day' when I definitely heard discussions along the lines 'We've had ADS for years and we know it works, what's the statistics behind spending the extra money, especially as we've heard RCDs might be unreliable'.

David Stone said:

I will repeat my point, the product standard test is not real and is useless,

David, where is the evidence for that statement? Ought that not to be compiled and papers submitted?

Thank you all for the replies.

Graham has made some points backing up the 'official' opinion, however, there is little evidence to show they will work. As David has pointed out, the Tests to pass the Product Standard are very limited, and not related to real life scenarios. Comparing AFDDs to RCDs will never work, as anyone with a Tester can show that the RCD does work, and also that it is not over-sensitive. We have no way of knowing if an AFDD has worked to stop a safety situation. What about when a switch has dirty contacts and causes a spark when it is closed/opened? Would it trip then, or is the detection of that spark beyond its sensitivity?

How much of an arc is needed to trip them? Comparing to circuit breakers, no, we do not test those, but, there are manufacturers graphs showing when they should trip and at what current, so we have a reference for their use, AFDDs have no practical data available, which will continue to cause consternation when we are compelled to fit them, but cannot back up their use, except to say 'it is mandatory in BS7671'.

Thank you all for the replies.

Graham has made some points backing up the 'official' opinion, however, there is little evidence to show they will work. As David has pointed out, the Tests to pass the Product Standard are very limited, and not related to real life scenarios. Comparing AFDDs to RCDs will never work, as anyone with a Tester can show that the RCD does work, and also that it is not over-sensitive. We have no way of knowing if an AFDD has worked to stop a safety situation. What about when a switch has dirty contacts and causes a spark when it is closed/opened? Would it trip then, or is the detection of that spark beyond its sensitivity?

How much of an arc is needed to trip them? Comparing to circuit breakers, no, we do not test those, but, there are manufacturers graphs showing when they should trip and at what current, so we have a reference for their use, AFDDs have no practical data available, which will continue to cause consternation when we are compelled to fit them, but cannot back up their use, except to say 'it is mandatory in BS7671'.

alanblaby said:

Graham has made some points backing up the 'official' opinion,

Small point of order: I'm not allowed to offer an official opinion. I'm helping the discussion along.

I would like some more information from BOTH sides of the discussion to be honest, but particularly the 'Nays'

alanblaby said:

What about when a switch has dirty contacts and causes a spark when it is closed/opened? Would it trip then, or is the detection of that spark beyond its sensitivity?

All we are doing if we accept that, is saying we don't know much about the device (which is understandable, because they are a new thing).

alanblaby said:

anyone with a Tester can show that the RCD does work

The RCD test set is only arranged to demonstrate the requirements of the RCD product standard with respect to tripping time met (although perhaps not now, because BS EN 61557-6 is not aligned with BS EN 61008 and BS EN 61009 on the test current that requires the device to operate in 40 ms).

The test will definitely not demonstrate that an RCD will really work in a given situation, which left some electrical installation experts scratching their head when investigating children dying of shock in a bath tub in Germany, where the RCD did not operate at all. (I think we've discussed this in the Forum previously - there is no residual current if the bath tub is plastic and the individual receiving shock is not touching any other metalwork connected to the earthing or bonding system. There is only L-N current, which does not operate an RCD.)

alanblaby said:

Comparing to circuit breakers, no, we do not test those, but, there are manufacturers graphs showing when they should trip and at what current, so we have a reference for their use,

Agreed, I think "time tested" comes into play here ... but the point I was making is that circuit-breakers can be affected by the environmental conditions, and not operate as expected, which is a minefield of "unknowns", but at least we have the standards to back us up if something goes wrong.

We have that with AFDDs also.

alanblaby said:

which will continue to cause consternation when we are compelled to fit them, but cannot back up their use, except to say 'it is mandatory in BS7671'

Which brings us right back to the lines of some discussions regarding RCDs 'back in the day' ...

"Which brings us right back to the lines of some discussions regarding RCDs 'back in the day"

Thankyou for you reply Graham.

Ok, RCD testers were not freely available then, and fuses were still more commonly in use than CB's in the early 90's, but we are in different times now, with freely available data to anyone with an internet connection, so what I am saying is, why arent there freely available data sheets showing that the AFDD will trip if your fridge is sparking for more than 3 seconds?

If we had that data, we could say to the customers that their appliances are not made to a good standard , so this device will detect a fault and make sure it will not catch fire if it is fitted. But we havent got that data, and, it seems to me, the Manufacturers of the AFDD's do not want to publish when their devices will , and wont work.

SPDs are similarly new protection devices, but papers are available to show when they will work, when they will have a marginal defence and when they will not work. It is easy to show a customer this, and say this extra £60 will probably save your boiler PCB if there is a surge nearby.

If the Manufacturuers were more open about the products, we could, maybe, defend them, and push their use through safety reasons, but at the moment, there is little reason to say 'this will save your house burning down due to an appliance fault'. 

And we are back to appliances. It's been mentioned earlier in this thread. Why arent the Appliance makers fitting these, or, mandated to fitting these? Because they already meet a product standard, so, the standard isnt being enforced, or is a poor quality standard, such as what happened with the 'non-flammable/self extinguishing' consumer units, which did not meet product standards, yet were being sold as meeting that standard. I cannot recall any prosecutions because of that, why is that?

alanblaby said:

why arent there freely available data sheets showing that the AFDD will trip if your fridge is sparking for more than 3 seconds?

I guess that needs to be defined. What "sparks and arcs" specifically?

Those defined in the product standard? If so, then, well the devices are tested to that.

But it seems there's a mist-trust of the product standard as well? As I've said before, if the product standard is wrong, that needs to be addressed ... but evidence will be required.

alanblaby said:

SPDs are similarly new protection devices

No, they're not! The difference is the increase in use of electronic devices means the widespread need for them is new ... but I can assure you I've been using SPDs since the early 1990s, but they existed long before then https://electricalcontractingnews.com/news/what-you-need-to-know-about-spds/ ... and prior to that, "tube arrestors".

alanblaby said:

If the Manufacturuers were more open about the products, we could, maybe, defend them, and push their use through safety reasons, but at the moment, there is little reason to say 'this will save your house burning down due to an appliance fault'. 

So, I can definitely see this point. The people to ask, however, are the manufacturers.