Zoom, it's no good trying to decrypt this stuff. What is defined as 'a stable electric arc'?

A more pertinent question to ask might be: ' What is the minimum energy value and arc voltage for a series arc in a ring final circuit?' Which, as we know, is what most domestic installations have in one form or other.

On the subject of SPDs, I think there are 2 classes. The first, is where an installation has been constructed, the purpose of which is to provide a mission-critical service, so, for an example, we might have something like a server farm which must be always on, 24/7 and have some baseline resilience against outages. The supply will most likely be 3 phase with back up UPS in abundance. Here, a SPD may be seen as another layer of 'defence in depth' against the possibility of interruption of supply.

This particular species of SPD most likely works and will give additional protection against lightning strikes into the bargain. It will also have an eyewateringly high price tag.

Then, we have another class of device for a totally different market, the domestic one, where joe blogs's 4K smart telly might get zapped by an interruption caused by a steadily deteriorating underground supply cable because the DNOs have been paying out to shareholders instead reinvesting into the distribution network infrastructure.

So, we end up with a very cheap jellybean set of components - electrical lego if you like, chucked into a cheap plastic case and mandated via some very spurious dataset which must have been crossed with that of a tropical country, and chucked into domestic consumer units with gay abandon and much financial gain.

I fear that like AFDDs, and the BS7671 changes which mandate them. the domestic side of these things promise the earth, yet deliver a mere handful of soil when called upon to function as described 'on the side of the tin'.

A.F.D.D. with a combined M.C.B. unit, the tripping may just be due to overcurrent, so we may not know which part of the device has caused the tripping off.

All the ones I looked at had some means of indicating the cause of the trip - usually coloured/flashing LED - different flashes for Arcs, RCD or overcurrent - so probably better than many an RCBO.

  - Andy.

I wonder if the flashing sequence for 'arcs' is triggered under the 'Don't know' category'?

1. Has anybody in here got them?

2. Does anybody in here intend to fit them?

Answer = no and no from me.

Zoomup said:

Q.3 When required for additional fire protection, RCDs shall be a rated residual operating current not exceeding 300 mA. Why is the minimum AFDD tripping current of 2.5 A so much greater than 300 mA?

The RCD would only trip on a live conductor to PE (or Earth) fault.

The 2.5 A, I understand, relates to the load(s) downstream of a broken conductor (rated 2.5 A or more) causing a series arc. The AFDD may still well operate for a parallel arc ... to PE, but would operate for parallel arcs L-N (or L-L)  if we had three-phase devices or other systems for which the AFDD were rated) which an RCD would not operate for.

Yes, I understand the issue with the fact in houses we often use T&E ... but not always ... and other cable types and wiring systems are used in other premises where AFDDs are required in Amendment 2 - and, of course, other wiring systems are used in appliances as has already been discussed

"Same question asked about RCDs. That's the only reason we ever had RCD testing."

But with R.C.Ds the test button tests the whole gadget, the electrical and mechanical aspects of the device. No test gear needed.

Z.

The biggest objection to fitting this new expensive stuff is the cost. The new stuff has virtually all arrived together. S.P.Ds, A.F.D.Ds, new types of R.C.D. that advertise that they are resistant to D.C. "blinding". The consumer just can't be expected to pay for stuff that they do not understand and can't possibly afford.

Z.

"Joyce, was it dot dot dash or dash dash dot for a trip by a arc fault?"

"No John I think it was dot dot dot dash"

"Fred's down the road is green, red, red.

"Where's that instruction sheet that the sparks left"

"Oh, I think that the dog ate it"

"Lets go online"

"We can't, the powers off and the router has crashed".

"Oh Ek!" "And wasn't Fred's green, green, red?

Z.

Zoomup said:

The biggest objection to fitting this new expensive stuff is the cost.

Yes, that was the case with RCDs. I'm sure the cost will come down ... already started to happen.

Zoomup said:

The consumer just can't be expected to pay for stuff that they do not understand and can't possibly afford.

421.1.7 Arc fault detection devices (AFDD) conforming to BS EN 62606 shall be provided for single-phase AC final circuits supplying socket-outlets with a rated current not exceeding 32 A in:
• Higher Risk Residential Buildings (HRRB)
• Houses in Multiple Occupation (HMO)
• Purpose-built student accommodation
• Care homes.
NOTE 1: Higher Risk Residential Buildings are assumed to be residential buildings over 18 m in height or in excess of six storeys, whichever is met first. It is anticipated that in many areas higher risk residential buildings will be defined in legislation which can be subject to change over time, as well as in risk management procedures adopted by fire and rescue services. Current legislation should be applied.
For all other premises, the use of AFDDs conforming to BS EN 62606 is recommended for single-phase AC final circuits supplying socket-outlets not exceeding 32 A.

In the highlighted part ('shall'), likely only the first bullet would be consumers as the client? In those premises, is it not pertinent to simply say it's there to help protect against fires? Just plain and simple? Any further questions in those premises, the answer could be "Introduced in the Amendment following Grenfell".

So, no long explanations.

Similarly, it could be offered in other premises quite easily, "There's a new device available to help stop fires. A bit expensive. Would be required if I were doing this job in a block of flats ... recommended in the Wiring Regs."

Zoomup said:

"Oh Ek!" "And wasn't Fred's green, green, red?

I agree ... what's more frustrating with the situation about indications, is that there's actually a standard that could be used, BS EN 60073. Yes, it applies to industrial controls and similar uses, and not mandated for other products, but nevertheless, would provide some uniformity to the situation regarding colours of indications and use of that with flashing etc.

Much better than "well, a blue LED looks good, let's just confuse everyone and use that. Now, how many flashes for standby?"