AFDDs for single-socket circuits

[Selfmade]

Haven't been on here for a while, so sorry if this has been discussed before.

BS7671 2018 + A2 Regulation 421.1.7 recommends AFDDs for "single-phase AC circuits supplying socket outlets..." (requires in certain premises). My intention is that from September 27th I will recommend them to customers (in practice I already do in some situations) and require a signed waiver if they don't want the expense. At least I will do so for the actual Sockets Circuits - typically ring final, serving a number of sockets for general use and sometimes also fixed equipment via FCUs.

What I'm not sure about is circuits that serve just a single socket, such as a dedicated circuit for a fridge or an oven. In the case of a fridge, it will likely draw less than 2A, so an AFDD is unlikely to perform any useful function. In the case of an oven, one could justify cutting off the plug and connecting it via an FCU, in which case the circuit is no longer supplying a socket, yet with or without a socket it's still the same appliance and the same wiring. Yet in both cases if a socket is fitted an AFDD is recommended according to the regs.

BTW I understand a case could be made for AFDD protection for an oven and oven circuit. But for this question I'm just interested in the definition of 'circuits supplying socket outlets' for the purposes of this recommendation.

 

[Dustydazzler]

Will my TV blow up if I don't fit an AFFDDD ?

 

[DPG]

Yes AFDDs are only a recommendation but after September will need a waiver signed by the client to say they dont want them, which will cover you when their tv blows up and they say you didnt recommend using one

If their TV blows up? I think you are confusing AFDDs with SPDs.

 

[pc1966]

My own belief is SPDs (and metal CU) are both good things to justify the cost and regulations behind them. The SPD is typically well under £100 now for the whole domestic installation* so not too onerous when doing a CU change or similar. Also SPD are likely to reduce the failure rate of some items, but probably not that much compared to not buying cheap crap in the first place.

AFDD are an item I am sceptical about for the reasons that @UNG has already outlined. I asked the speaker at the recent "18th AM2" event CEF held about it and he told us, perhaps a bit superciliously, just to trust the manufacturer's self-test on this. In my view if you can measure/verify something then it really fails on the purpose and specification front.

[*] If you have a big installation with multiple DB and it has a lightning protection system you might need type 1 at then incoming point and also type 2 SPDs at the other sub-DBs.

 

[pc1966]

In terms of the OP's original point I don't see any problem with offering AFDD as an extra-cost option for properties where they are not mandatory but it is going to be only a few who will spend the extra on them. Not sure anyone has written a fair and balanced guide for the public on this yet?

Perhaps in a couple of years they will be down at similar prices to RCBOs and then less of an issue, but we still have to see how well our AFDD fare in terms of unexplained trips versus the poor reputation the American AFCI have.

 

[DPG]

Although I get it that some people are reluctant to fit AFDDs partly because no testing can be done, bear in mind we don't test MCBs either.

 

[Dustydazzler]

Although I get it that some people are reluctant to fit AFDDs partly because no testing can be done, bear in mind we don't test MCBs either.

The fact we can't test them is neither here nor there Imo , as you say we fit millions of MCBs each month and have no idea if they work proper or not.
My issue with AFFDDDs is I honestly don't feel that they are necessary in the UK

 

[DPG]

The fact we can't test them is neither here nor there Imo , as you say we fit millions of MCBs each month and have no idea if they work proper or not.
My issue with AFFDDDs is I honestly don't feel that they are necessary in the UK

Yes, but I was specifically referring to the issue that gets raised about being unable to test them.

 

[Dustydazzler]

Yes, but I was specifically referring to the issue that gets raised about being unable to test them.

From what I have seen on YouTube from America the more expensive AFCI / AFFDDDs are Self Testing

 

[GBDamo]

if houses and flats were burning down left right and centre due to loose connections and arc faults then I would be the first to be pricing AFFDDDs to my board swaps. My clients for most part are very well off and wouldn't bat an eyelid to a new £2000 consumer unit.
I just haven't seen enough evidence in front of me to suggest AFFDDDS are really a necessary Evil

Quite, AFDFs are a solution in desperate need of a problem.

 

[davesparks]

Yes AFDDs are only a recommendation but after September will need a waiver signed by the client to say they dont want them, which will cover you when their tv blows up and they say you didnt recommend using one

Which regulation states that a waiver is required?

 

[Dustydazzler]

Quite, AFDFs are a solution in desperate need of a problem.

Agree

They are invention ahead of their time as the problem hasn;t been invented yet

 

[davesparks]

The fact we can't test them is neither here nor there Imo , as you say we fit millions of MCBs each month and have no idea if they work proper or not.
My issue with AFFDDDs is I honestly don't feel that they are necessary in the UK

Yes we do, but MCB's are batch tested and generally proven to be a pretty reliable technology. Plus they are a fairly basic mechanical device which doesn't rely on electronics.
Plus if an MCB is tripping it is almost always possible to find the cause with regular test equipment that we all have. We can pretty easily test whether an MCB is over-sensitive.

Afdds are presumably also batch tested, but they rely on sophisticated electronics to work which increases the opportunity for failures, especially when engineered down to a price.
We have no way of realistically testing for what may have caused an afdd to trip at the moment, and no way to work out if it is being over-sensitive.

 

[Dustydazzler]

I remember a few years ago watching a YouTube video of an electrician trying to get to the bottom of a tripping AFCI on a socket circuit on a new house. He couldn't get the AFCI to hold in SO guess what he did...

Removed the AFCi and put the circuit on a standard MCB

If that is the American solution to a tripping AFCi then why bother in the first place ?

 

[Selfmade]

Although I get it that some people are reluctant to fit AFDDs partly because no testing can be done, bear in mind we don't test MCBs either.

True, although at least in the event of an MCB trip we can break up and test sections of the circuit to find the location of the fault.

 

[UNG]

Although I get it that some people are reluctant to fit AFDDs partly because no testing can be done, bear in mind we don't test MCBs either.

If we wanted to spend a lot of money there is test equipment available for MCB's, I have done many searches for AFDD test equipment and found none

The fact we can't test them is neither here nor there Imo , as you say we fit millions of MCBs each month and have no idea if they work proper or not.
My issue with AFFDDDs is I honestly don't feel that they are necessary in the UK

MCB's are so cheap that no one really bothers if a suspect one is replaced, a suspect AFDD replacement is a considered cost and the decision can't be taken lightly

From what I have seen on YouTube from America the more expensive AFCI / AFFDDDs are Self Testing

How do you have faith and trust in a self test, the AFDD says it is working correctly so it must be right and the circuit is faulty and so the pantomime starts. It says it all with AFDD's when Hager has produced an AFDD that can be reprogrammed to ignore circuit noise that the AFDD may inadvertantly react to

Afdds are presumably also batch tested, but they rely on sophisticated electronics to work which increases the opportunity for failures, especially when engineered down to a price.

And firmware / software that could become corrupt from mains noise or voltage spikes is that why the SPD came before the AFDD

We have no way of realistically testing for what may have caused an afdd to trip at the moment, and no way to work out if it is being over-sensitive.

As previously mentioned Hager do have monitoring tools and their AFDD can be reproogrammed but I can't help but feel it's a kings new clothes situation you programme out the senstivity and all you end up with is a fancy bit of kit in the box to meet the requirements of the regs but it performs no other function

In recent years we have had requirements to fit SPD's and now AFDD's but nowhere have I seen any documentation, facts or real world reasons / case studies to support there introduction or to enable us to better inform our clients and customers as to the benefits of having them installed in their installation