AFDD performance standards, installation for a timber framed new build

I strongly advise you to find that man before you start the design.


I think you going to find it very difficult to persuade someone to put their name against your design & installation let alone when its already been buried in the fabric of the building.


I, for one, wouldn't take that on.

Granted that much domestic design is probably done on the hoof and by rule of thumb, but there must be a reason why design (C&G 2396) is at level 4, but installation and initial verification is at level 3 (C&G 2391).

It is abundantly apparent that a lot of sparks remain to be convinced about the worth of AFDDs but, perhaps more importantly, so do a lot of fire safety professionals. From my perspective, anything that mitigates the risk of ignition is worthy of consideration. However, at this stage I think I would rather invest in a comprehensive early detection system with some well-placed emergency lighting in my property rather than AFDDs.  Trumping it all, of course, is careful design of your escape. 

I do wonder what insurance companies make of setting aside recommendations made in national standards. That is bound to be something that will eventually be tested.

I think you going to find it very difficult to persuade someone to put their name against your design & installation let alone when its already been buried in the fabric of the building.

The OP might be thinking of just building regs certification - the local building control dept (or one of the private firms offering equivalent) will happily issue a building regs completion certificate if they've had a modicum of oversight during the process.


As for AFDDs themselves, I'm in the 'not proven' camp myself. My feeling is that for the money you could probably use alternative approaches that might give similar levels of protection (at least for the fixed wiring) using better understood (and possibly more reliable) approaches. I'm thinking of things like wiring systems that surround the conductors with earthed metal and steel backboxes for accessories - so that any arcing that could start a fire, if not contained, would be very likely to result in an earth fault and so can be caught by conventional RCDs or overcurrent protective devices. That sort of approach would also give some protection from resistive heating faults, which AFDDs are unlikely to spot. On the other hand AFDDs can provide protection beyond the fixed wiring (e.g. to appliances and their flexes) - so maybe a mixed approach - e.g. AFDDs just on socket circuits might be worth considering.


   - Andy.

Thanks for the input.  Some interesting ideas for me to consider. 


I have indeed found an electrician to work with me.  It turns out the the local building regulations people are obliged to provide a service to DIY'ers like myself, in this case it is outsourced to a local company who do 3 inspections and a formal test.


I had a lot of trouble from the local "closed shop" electricians who all refused. Never mind the fact that I am a Chartered Electrical Engineer with years of experience. I asked one guy if he knew what "Lenz's Law" was, he went off in a hump....

Hi Thomas.


I think you would be better off putting in a comprehensive fire detection system, sprinklers, or both.  Using "LSZH" type cables rather than PVC insulated will also be a benefit for two reasons, a) less smoke and acidic gas produced during a fire, and b) XLPE insulated conductors will dramatically reduce (in theory to zero) the chance of arcing occurring within damaged cables.


AFDDs, in my view, are not a panacea that some might have you believe, and they will not detect ohmic heating type faults (which probably account for most electrically started fires).


I can provide you some research work (yet unpublished) if you PM me with your details.  It might be interesting to you.

b) XLPE insulated conductors will dramatically reduce (in theory to zero) the chance of arcing occurring within damaged cables.

That's very interesting - how does that work then?


   - Andy.

Hi Andy,


This starts with Paschen's Law, which would indicate that the distances over which arcing at 230V RMS can occur are tiny.  Of the order 7.5um.  At that scale, an initial arc can itself change the spark gap distance by burning away conductor material.  Research, as carried out by the manufacturers of AFDDs and others, seem to all rely on arc-tracking known as "arcing over char" which itself is reliant on a carbonaceous path bridging the discontinuity (break in conductor etc).


If you heat PVC insulation for a long time, it can decompose leaving char.  It is over that char that arcing is said to occur.  Of course you also need to believe the back-story as to how the PVC became subjected to such mistreatment to then later consider if arcing was ever a possibility.


PE and therefore XLPE materials do not decompose in the same way, they tend to gasify and or become ash but do not leave char.


No char, no arc.


Situations in equipment may be different of course as you quite rightly point out.