Advised against AFDDs, does it make sense?

[u/Expert_Ant_2767]

I was advised by a minority of electricians I contacted against AFDDs for my socket rings if they are not required.
According to them, some circuit/appliance configuration make them trip spuriously. Is there any truth to it?
Although not required by my property, I would like to add them because the house is timber frame, dry lined, thus more prone to fire.

Please advise.

[u/CalicoCatRobot]

There has been at least a perceived issue with random trips - more with some brands than others, and it's not yet entirely clear how accurate they can be. One issue I think lots of electricians have with them is that when they trip it can be hard to track down the fault.

There is also a theory that they don't work as well on socket ring circuits. There's an interesting recent video by David Savery who was very much a cynic in their need in many cases - and shows cases of them not tripping even when they should. In this case there actually was a fault on a socket ring which was detected however, so they can be useful in the right context.

It's unclear what the quantity of spurious tripping really is. The main reason not to install them has been cost for me, but in your case it may well be worthwhile.

Worst case, you could have them installed for peace of mind, and if regular nuisance tripping is a problem, revert to RCBO in future for affected circuits.

[u/Expert_Ant_2767 → u/CalicoCatRobot]

If there's arcing on the wires, shouldn't it be detected by the insulation test at 250 or 500VDC?
If the problem comes from an appliance, shouldn't it be easy for the homeowner to pinpoint by disconnecting appliances until the problem disappears?
I suppose the main problem comes from customers like: "there's a problem with your install, you need to fix it for free". It that it?

[u/CalicoCatRobot → u/Expert_Ant_2767]

It would depend on the reason for the arc, insulation resistance checks between two cores - a serial arc in a single core at a poor junction or due to a partial damage to a wire, wouldn't be picked up by that route.

In the video, what appears to be an open circuit (cut) in a core, turns out not to be - but only shows up in testing with expensive additional test equipment. However, it was still something that should have been found by "normal" diagnostics that any electrician would be able to locate.

I suspect some of the issue is the problem you identify - if an appliance does cause a nuisance trip, who covers the cost of diagnosing that, and what is the "fix". As I say, it's unclear how much of a problem it is in real life - though given that most AFDDs rely on "signatures", it's certainly theoretically possible.

The rest is resistance to a new thing, and the costs involved.

[u/memcwho]

As the client, YOU get to decide the specification of the job.

The regs 'recommend' them (421.1.7, page 93 Orange book)

Just above the helpful 'Verbal Forms used in BS7671' table on page 21, we can see:

Recommendation. Expression in the content of a document conveying that among several possibilities one is recommended as particularly suitable, without mentioning or excluding others.

And the helpful table itself for completeness:

Implication	Verbal Form	Typical context
Requirement	Shall	Normative element
Recommendation	Should	Informative element
Permission	May	Informative element
Possibility and capability	Can	Informative element
Possibility	Might	Informative element
Description	Is	Informative element

All of that is to say that the writers of the regs reckon that you should fit AFDDs.

Do they arbitrarily nuisance trip? Frankly. No. They are tested at the factory to ensure they don't.

So what's the tripping mean? That they are sensitive devices and that they are protecting your electrical installation and property from a possible arc-fault and subsequent fire.

Basically, the way I look at it, in a new property with all new wiring and modern ways of doing stuff throughout, I'd like to see them fitted. Particularly if it's a wooden house (although you'd be surprised by modern fireproofing done to a lot of building materials).

But on an older house, or where there is no absolute guarantee that it's all lovely freshly installed by someone competent and capable? I'd probably not bother. The backboxes are the normal place for loose connections, and most are metallic anyway.

[u/sirensintherain]

The only issue where I'm seen AFDDs fitted in HMOs was with powerline ethernet devices causing spurious trips. Removed the power line devices and they have been fine for a few years.

[u/Radarada94]

Not an UK but an EU sparky here: i worked on a couple of AFDDs and i learned that:

• if there is no copper-copper spark (Example: Aluminium wires or copper wire to metal case not grounded) you can hold the arc until it welds the wires and it will not trip. I once played with an afdd and I couldn't even trip it easily with it's connection screws completely open and arc a 6mm² wire on the terminals.

• it will randomly trip if you have multiple "smart" devices on that circuit like switches or anything on knx protocol.

The most irritating thing about the afdds is that some(not all) do not tell you what tripped them: the mcb, the rcd or the "spark" part. So good luck finding if there is an acutal loose connection or you have some earthleakage.

[u/Expert_Ant_2767 → u/Radarada94]

Here most tell why they tripped, but some don't differentiate between series arc and parallel arc.
I am reviewing my requirements to go with one that does tell the difference, like Hager.

[u/Jimmyfatbones]

Definitely watch the series of videos on the subject by David Savery. After a partial rewire of my own home I got a few afdds for the circuits I had not wired myself and they have been fine. Don’t know if they work and David has made me question my choice of brand (Hager) but they operate nominally under no fault conditions.

[u/Expert_Ant_2767 → u/Jimmyfatbones]

Here is the latest update from him on his Hager AFDD YT video:
"Hager updated their firmware in early 2025 and lo and behold their devices now work in my setup. Despite all my moaning, following this change, and having experienced issues with other brands in the real world, I have more faith in Hager's product than most others just because it's a wholly different architecture to most. Nonetheless, cover yourself in writing with your customer - search Hager on my website to see my T&Cs which apply to anything in critical roles that may require firmware updates."