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Electrical installations domestic

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Re: Electrical installations domestic

Postby AJB Temple » 06 Apr 2021, 10:07

Happy Hacker - I would very much appreciate that checklist or guide you referred to written by a friend of yours. I will PM you.

Also meant to thank SPB for his input.

I think elements of the rules cause confusion because changes are not well explained. Metal CU's being one such example. The question comes up in forums sometimes as to whether a CU can be mounted on a wooden backer (say plywood cladding on a wall within a cupboard) or whether it must be mounted on intumescent material. I have not referred back to my recent 18th Ed copy but I think it is silent on the matter. You just need not to have potential causes of fire (like live bits poking out).

The Tesla example of earthing I gave above was when Tesla were ramping up their sales about 3 years ago. They provided a domestic charger unit with the car. This was confusing to a number of electricians as CPC arrangements were not super clear at first so an electrician had to look carefully. My friend the electrician went to far as to consult building control on our first one. There was no issue with TT rod at my rural house, but my partner lives in a built up street in London and goodness knows where metal gas and water pipes may be underground. The system was equally confusing to users, as the charge points arrived pre-set to the minimum charge rate (the "takes forever" setting). Anyway, I digress. Has proved to be a very helpful thread for me.
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Re: Electrical installations domestic

Postby 9fingers » 06 Apr 2021, 10:24

I've found it helpful too in that for my purposes with a few rentals to get checked, a professional test every five years is relatively cheap insurance provided I can actually get a sparky to give me an appointment. All seem to be silly busy atm.

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Re: Electrical installations domestic

Postby AJB Temple » 06 Apr 2021, 11:10

Kevin

I note your comment on AFDDs. What is the reason for the comment may I ask? It's obviously outside of my expertise (though I know what they are) but we do have an arc protection device and surge protection on one of the sub consumer units. Everything is Hager now throughout this property.

The reason for fitting it was that we had to install a backup device in a remote location (ie my house) that connected with the financial markets (It is actually a CREST server) and the spec required AFDD among other things (cooling mainly). I hadn't given it a second thought until your post. The CREST server is now gone and the device is therefore redundant in that single purpose sub-CU but could be relocated.

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Re: Electrical installations domestic

Postby spb » 06 Apr 2021, 11:42

My gut feeling on AFDDs is that, like metal consumer units, as soon as a recommendation to use them outside of very specific situations comes in, there'll be a flood of chancers selling £80 EICRs and claiming the entire installation is non-compliant and therefore unsafe because it doesn't have arc fault detection, never mind that it's only two years old. The difference is that with the cost of AFDDs at the moment - not to mention that for some manufacturers they're still two-module devices that need a separate RCBO as well - just the material cost to fit them everywhere runs into the thousands for a normal house.

This isn't to say anything against AFDDs themselves - I have them on my garage/workshop socket circuits, because it was wired from scratch and the extra cost of two of them on top of all the cable, conduit and accessories wasn't too bad - but like many well-meaning regulation changes I'm quite sure it'll be abused for a quick buck.
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Re: Electrical installations domestic

Postby HappyHacker » 06 Apr 2021, 14:38

Adrain, PM me your email and I will send you a copy, thanks for your PM.

My issue with AFDDs is do they actually work in real life situations? I looked at America where they have been using them for a number of years. They originally claimed there would be a massive reduction in fires caused by arcing faults a reason for introducing them. From the figures available I could not see any significant change in electrical fires that could not be explained by more new houses and updating of old wiring. Also a lot of the figures assume that an electrical fault/fire is always caused by an arcing fault without any further analysis. The lower voltage used in America results in higher currents and the different wiring practices with less installation testing and a greater reliance on constructing to the code make comparisons with our installations difficult.

AFDDs use a computer to analyse the waveform to determine if there is an arc occurring. As arcs occur when switches are operated and brushed motors start the software has to differentiate between faults and normal arcing. There are numerous videos on youtube showing people trying to get AFDDS to trip by generating arcs and generally not succeeding. Apparently using a carbon electrode is the best way of causing an arc that will trip an AFDD. I am told the computers are programmed to trip with the standard test waveform used by the testers which should be the same as a proper fault arc.

I have no problem with installing additional safety devices if they work but am yet to be convinced that AFDDS do provide an additional level of safety worth the cost. Are they just the result of good marketing/lobbying?

I can see a householder with a quote of >£2000 to replace their consumer unit with the full complement of AFDDS from a Part P electrician instead approaching Fred from the pub who will do the job for £600 using a £100 CU from one of the sheds with no AFDDs, no testing and no paperwork and it will only take him a couple of hours and as a favour he will put all the lights on one RCD/RCBO due to borrowed neutrals causing tripping otherwise. Or they will stay with the old rewireable fuse CU with no RCDs.

I have a very intelligent and very rich customer who I spent nearly 10 years trying to get to update his old Wylex rewireable CU to one including RCDs/RCBOs for improved safety for hm and his family. I failed and gave up a few years ago. I did get a callout to change a fuse wire for him before Christmas and I admired his new Porsche!

Please don't get me started on metal consumer units especially with TT installations of which I used to do quite a few.
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Re: Electrical installations domestic

Postby AJB Temple » 06 Apr 2021, 16:22

Thanks Kevin. That does all make sense. Thank you for taking the time to explain. I suppose that my assumption was and maybe still is, that kit supplied by a reputable manufacturer such as Hager, properly installed, is likely to work. It is not clear to me why the arc protection was needed as really all that a CREST machine is, is a rack mounted computer that is remotely monitored for down time and operates in a temperature controlled and secure environment. There is nothing at all special about it and I could not see any aspect particularly justifying the specified protection.

PM on its way. I meant to send my email address earlier. Adrian
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