Amendment 2 and AFDD's

[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.

 

[pc1966]

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.

Or return to the old Wylex board style of double screw terminals?

The Wago style of spring loaded ones were something I looked at with deep suspicion when they first came out, but it turns out they (with clean cable, etc) give a good reliable connection and no need for someone to have either proper experience and training, or to have and use a torque screwdriver to get reliable connections.

 

[Dave Appleby]

And nothing protects against THIS!

Big shout out to SPN who were brilliant yesterday. Onsite in under 90 minutes. Fixed in 30 more.

 

[stevethesparks]

Or return to the old Wylex board style of double screw terminals?

I'm a big supporter of that, particularly on the main switch terminals.

 

[newfutile]

the new Wylex boards have double screw terminals on them , which was a pleasant surprise

 

[brianmoooore]

And nothing protects against THIS!

Big shout out to SPN who were brilliant yesterday. Onsite in under 90 minutes. Fixed in 30 more.

Wouldn't any downstream AFDD that was loaded detect this and switch off. The current passing through the AFDD will be varying with an arc's signature whether the arc is before or after it.
If all loads were AFDD protected, the current through the cut out would fall to zero and the resistive heating would stop.

 

[pc1966]

Wouldn't any downstream AFDD that was loaded detect this and switch off. The current passing through the AFDD will be varying with an arc's signature whether the arc is before or after it.

That assumes it was arcing, and not just a few tens of mOhm resistance heating.

 

[LastManOnline]

That assumes it was arcing, and not just a few tens of mOhm resistance heating.

Yes. And not even a few tens of ohms is required. A half ohm (poorly tightened main fuse) will produce 30 Watts of heat in a fuse enclosure under full load. . Added to the heat produced by the fuse under normal working circumstances.

 

[pc1966]

Yes. And not even a few tens of ohms is required. A half ohm (poorly tightened main fuse) will produce 30 Watts of heat in a fuse enclosure under full load. . Added to the heat produced by the fuse under normal working circumstances.

I was talking of milli-ohms.

Say 50A (shower and/or cooker) & 0.05 ohm = 125W

 

[LastManOnline]

I was talking of milli-ohms.

Say 50A (shower and/or cooker) & 0.05 ohm = 125W

My error. Never saw the little "m". Next stop.. specsavers