Amendment 2 and AFDD's

[Dave Appleby]

Hi.

Been reading the but around 427.1.7.

Does anyone have any idea on retrospective application?

Is this going to apply to every board change or just adapted to new builds and then as a C3 recommendation for everything else?

Given prices it's going to be a massive cost change on a board swop. Plus, I know for certain I'm going to have space issues with anything over 30 years old here in Fife.

Thoughts?

 

[Norah Nabino]

So is there no AFDD which can be installed and protect multiple circuits (like an RCD on a dual split board for instance)?

Not yet,most of them are for individual circuits

 

[Dustydazzler]

I personally wouldn't want an affdddd covering 5 or 6 or 7 circuits

for me its individual units or not at all

 

[IAmSparkytus!]

Ive never seen them put into practice so wasn't sure how sensitive they are. I was just thinking it would make things a lot cheaper until the prices came down. Much like when dual split boards were much cheaper than full RCBO boards but now the prices have dropped.

 

[pc1966]

I did read over the proposed amendment and AFDD are not being pushed for lights or high current loads like showers. Odd really, as most seriously burned out examples I have seen have been shower circuits, but maybe good old fashioned resistance and so no arcing to make one trip?

So it might be a case that really they only get used for sockets, in which case I foresee the return of a single/dual RFC per property!

 

[LastManOnline]

Hager has a document claiming that they work on RFC's but acknowledge that only if the fault is on a spur or appliance connection

Helpful link. Confirming then what we suspected, that RFC fixed wiring is not protected against a series arc, except in the extremely unlikely scenario of 2 arcs taking place simultaneousely.

 

[LastManOnline]

So it might be a case that really they only get used for sockets, in which case I foresee the return of a single/dual RFC per property!

You may well be right. But it could just as easily happen that the introduction of the AFDD ends up heaping more negative press on the RFC due to its inherant unsuitability for an AFDD protected circuit compared to the radial, which does not share these limitations

 

[pc1966]

You may well be right. But it could just as easily happen that the introduction of the AFDD ends up heaping more negative press on the RFC due to its inherant unsuitability for an AFDD protected circuit compared to the radial, which does not share these limitations

No, you are not understanding the RFC limitation on AFDD.

They do detect arcs, it is just the "open ring" fault does not generate an arc (of any note) so it will not trip the AFDD. If you do get enough current flow and sufficient voltage to sustain an arc on some place in the RFC (so connection to socket or appliance) it will still detect it. So you might see that as a limitation on detecting faults, but then I really doubt that an open ring fault has ever caused a fire on its own as even the full 32A breaker limit on 2.5mm of one leg on a broken ring is overload, but more cable-life-killing and not fire starting temperatures.

 

[LastManOnline]

No, you are not understanding the RFC limitation on AFDD.

I don't think I, m misunderstanding it. The "open ring" won't detect an arc. The "open radial" will detect an arc.

So you might see that as a limitation on detecting faults,

It depends on how the "powers that be" promote the AFDD. Over here the the protection afforded to the fixed wiring is emphasised as heavily as the protection afforded to the appliances connected to the fixed wiring. Like you I don't have any major concerns about arcing in a ring circuit as I have not experrienced(nor yet been presented with) credible evidence for series arcs in fixed wiring causing fires. But I, m simply making the point that the introduction Aof the AFDD is unlikely to enhance the ring circuits appeal (with exception of UK)

 

[pc1966]

I don't think I, m misunderstanding it. The "open ring" won't detect an arc. The "open radial" will detect an arc.

Yes...but due to the open ring having practically no arcing.

It sounds very much like the arcing is a good thing here!!!

It depends on how the "powers that be" promote the AFDD. Over here the the protection afforded to the fixed wiring is emphasised as heavily as the protection afforded to the appliances connected to the fixed wiring.

Agreed, if it is for appliances then RFC or radial makes no difference.

Like you I don't have any major concerns about arcing in a ring circuit as I have not experienced (nor yet been presented with) credible evidence for series arcs in fixed wiring causing fires. But I, m simply making the point that the introduction of the AFDD is unlikely to enhance the ring circuits appeal (with exception of UK)

The RFC (in this context) only makes sense with fused plugs, and really only the UK and countries with a shared electrical history use the BS1363 plugs so the discussion is limited to them anyway.

The appeal of the RFC is around half the number of AFDD needed as half the number of circuits, and with a premium above RCBOs of £100+ per circuit that starts to make it attractive!

 

[e-spark]

Those that I've seen (Crabtree & Wylex) are single module RCBOs, with AFDD incorporated.

one of the Crabtree bigwigs is involved in writing and advising on the regs, no conflict of interest there then eh?
At current prices they arent financially viable to joe bloggs

 

[Norah Nabino]

I did read over the proposed amendment and AFDD are not being pushed for lights or high current loads like showers. Odd really, as most seriously burned out examples I have seen have been shower circuits, but maybe good old fashioned resistance and so no arcing to make one trip?

So it might be a case that really they only get used for sockets, in which case I foresee the return of a single/dual RFC per property!

Where is it stated they should not be used on shower cats?

 

[Cookie]

I did read over the proposed amendment and AFDD are not being pushed for lights or high current loads like showers. Odd really, as most seriously burned out examples I have seen have been shower circuits, but maybe good old fashioned resistance and so no arcing to make one trip?

So it might be a case that really they only get used for sockets, in which case I foresee the return of a single/dual RFC per property!

Burned up connections are typically not the result of arcing, but rather series resistive heating which happen to be behind 95% of all electrical fires.

 

[LastManOnline]

Yes...but due to the open ring having practically no arcing.

It sounds very much like the arcing is a good thing here!!!

Fair point. You have legitimately turned that around into an arguement that the RFC is safer than a, radial from an arcing point of view?

 

[pc1966]

Where is it stated they should not be used on shower cats?

It does not, but it said something like "circuits not exceeding 32A" which rules out many modern electric showers over 7kW or so.

 

[Aaron b]

Perhaps we should install all power circuits with parallel conductors. For another amendment/edition, all accessories could include another live terminal for high integrity supplies.