Wylex Combined AFDD/RCD/MCB

[Onoff]

I like this!

 

Having recently done my 18th I was left like many others thinking wtf when it came to AFDDs. As in what circuits to protect and if one why not all etc and how to implement without having a massive cu. I know 2 module units have been available for a while but this is a one module wide unit combining AFDD/RCD & MCB. Haven't read any further as to price and assume its single pole switching. Only just dropped in my inbox.

Edited September 18, 2019 by Onoff

[CC45]

How much are they?

[Onoff]

21 minutes ago, CC45 said:

How much are they?

 

Don't know...the 2 module wide ones are £100+.

[Ed Davies]

Do they work (as AFDDs)?

 

John Ward found a worrying lack of operation for another brand in this video: https://youtu.be/kVpXQa6EW3k

 

 

Starts on the AFDD bit about 15 minutes in.

[ProDave]

I am just quietly ignoring them.  Isn't there a lot of concern about spurious tripping?

[Onoff]

1 hour ago, ProDave said:

I am just quietly ignoring them.  Isn't there a lot of concern about spurious tripping?

 

Yep, allegedly they work on a better safe than sorry principle! ?

 

I just like the idea / technical aspect of the 3 in one...wonder if they make them double pole...

 

The conspiracy theorist in me wonders if they are in fact a subtle way of reducing demand on the grid...more take up = more trips = less draw! ?

 

 

[Jeremy Harris]

I may be lucky, but I've never, ever, seen a fire, or the possible start of a fire, caused by arcing.  I've seen loads of arcing damage, but 99% of the time this was secondary to an overload condition, something like a plug heating up, allowing the socket spring contacts to deform, so causing some arcing before the circuit naturally self-limited and went open circuit.  I've certainly seen arcing in switches, usually it just makes the switch defective, either permanently on or off, or just damages it mechanically so it stops working.  All these things look messy, but how many actually cause fires, so needing houses to be fitted/retrofitted with hundreds of pounds worth of (somewhat dubious it seems) AFDDs?

 

I get the feeling that this is a solution looking for a problem, that's being promoted by the manufacturers of the solution as a "must have".  There are a few other examples of the regs going a bit OTT in recent years, and I'm beginning to wonder if the IET are really doing a proper, validated, risk assessment before mandating that certain devices must be installed.  I should make it clear that I'm all in favour of RCDs etc, but I can't help thinking that banning ring finals, for example, would give a better safety benefit than mandating that AFDDs be fitted.

[dpmiller]

arcing is more of an issue with DC though, isn't it?

[ProDave]

I frequently come across burned out switches. The usual culprits are 20A switches or worse, FCU's used to switch an immersion heater. One I did recently the switch had burned out to the point of making a black hole in the front plate and inside the mechanism had completely crumbled to bits, but the plastic back box it was in was not even charred.

 

I suppose this is what we must expect of the organisation that decided the "solution" to CU fires was to put the CU in a steel box.  I always argued the solution should have been to take a long hard look at WHY CU fires happen and try to improve design, like go back to the old fashioned idea of 2 screws on all terminals, and mandate that if you are going to use cage clamp terminals, you design them such that it is physically impossible to put the busbar finger the wrong side of the cage clamp.  But no, we have not changed the design to stop a fire, just done something to try and contain it. And soon you will have to fit one of these expensive devices to detect the fault.

 

What is the betting these AFDD devices will still have a cage clamp terminal that has nothing to stop you inserting the cable or busbar on the wrong side?

[Onoff]

Its interesting than the change BACK to metal consumer units was in part due to poorly installed insulated ones going up in flames.

 

However one of the best examples of a consumer unit fire was the stately home one that was within a metal unit. From memory a knockout hadn't been glanded off an mice made a nest. It went up I imagine due to a loose connection and in effect became a wall mounted fire. Flames went up the handy metal conduits acting as chimneys and torched the place.

[Jeremy Harris]

I'm with @ProDave on the useless design of terminals now.  The older double screw terminals were way better, not just because they provided redundancy and more contact area, but also because they didn't deform the wire so badly.  Gate clamps are a PITA in my view.  Both because they have the ability for wires to be inserted but not clamped when the screw is tightened, but also because they often aren't very good at gripping bigger cables.  I did an inadvertent experiment recently, when wiring some 25mm² tails to an isolator .  I was wiring the panel on the bench, prior to fitting it in a box (just for easier access) and discovered that the 25mm² tails kept coming loose.  It seems that the slightest bit of movement will tend to loosen off the clamping force, even after the screw has been torqued up to the right setting twice.  It certainly makes a good case for tightly securing tails close to terminals so they cannot be wiggled  to see if they are secure, as this wiggling seems enough to loosen them off slightly.

[Ed Davies]

I wonder how much this is all botty covering. If there's a prominent fatal fire caused by arcing the immediate question will be: why aren't AFDDs mandated the way they are for bedrooms in the US and Canada? Because they're expensive. Money before lives? Outrage. Etc.

 

So then the question is, why are they mandated in bits of North America? And do any valid arguments there apply here with twice the voltage and half the current?

[Jeremy Harris]

28 minutes ago, Ed Davies said:

I wonder how much this is all botty covering. If there's a prominent fatal fire caused by arcing the immediate question will be: why aren't AFDDs mandated the way they are for bedrooms in the US and Canada? Because they're expensive. Money before lives? Outrage. Etc.

 

So then the question is, why are they mandated in bits of North America? And do any valid arguments there apply here with twice the voltage and half the current?

 

 

Good points.  The US electrical system has some features that make it safer than the UK system, and lots of features that make it less safe (IMHO).

 

The 180 deg bi-phase 240V LV  supply system, with N/PE at mid-line potential, is a plus, as the maximum potential between any line and ground is 120 VAC.  The radial wiring system that's universal in the US is also  plus point, in my view.

 

However, the really. really crap design of US plugs, the complete absence of fuse protection on appliance supply leads and the near-total absence of protective earthing, together with the absence of switches on power outlets, are all serious flaws.

 

Arcs are far more likely in US wiring schemes, as the absence of outlet switches, means that the probability of plugs being removed under load is high.  This pretty much always generates a disconnection arc, and a look around pretty much any US outlet will show marks where this has already happened.  Fitting snap action switches would probably remove the risk of most disconnection arcs on US installations.

[MikeSharp01]

This topic seems not have been mentioned much since this initial discussion. The several other places include:

 

 

and

 

So I thought I would poke it now as I have to decide on which circuits to fit Arc Fault Detection Devices (AFDDs).

 

The 18th regs seem to mandate them on sockets in all buildings not just the tall ones or HMOS etc, as 'recommend' is to be interpreted as 'should' the way I read it. AFDD devices have moved on a bit in the 3-4 years since the OP and you can now get single unit combined double pole with AFDD, RCD and MCB for around £120 (I have been looking at those from LEWDEN but others seem to be similarly priced.) 

 

So if I put them on the five radial (we won't be having any rings) 13A socket groups I am into £600 and then I wonder about the 5A lighting sockets, these are sockets after all, but as they are all fed via a DMX dimmer it is not obvious how and AFDD might respond to such a situation. 

 

Anyone any thoughts to add to this question and the wider AFDD debate four years on?

 

[Jenki]

I like the radials idea for sockets, but I wouldn't be spending £600 on AFDD'S.  there is so little evidence of Arc faults causing fatalities. IMHO, as has been said, this is a solution looking for a problem. 

Surge protection, yes 100%. 

[Jenki]

@MikeSharp01 , just got this in my inbox  Fusebox AFDD.