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Friday, 22 September 2017

The imminent rise of the AFDD in UK wiring regulations

Arc Fault Detection Device The AFCI technology using a different acronym AFDD, is on the horizon for implementation in the UK and many people are afraid.  Is this true and should we be afraid of change?

Some years ago I wrote a post on why the UK didn't use AFCIs while they are commonly used in North America.  In fact AFCIs are mandatory in the US and Canada to protect certain final circuits in the same way that RCDs, in the form of RCCB and RCBOs, are mandatory in the UK for most final circuits.  There has been a lot of grumbling over the pond about this technology but what does it mean for the UK.

The long and short of the article was the methodology of UK wiring was different and arguably less likely to be prone to certain types of faults. Mainly due to the statutory testing regime coupled with the conservative nature of the standards body in the UK. 
  • The equivalent of RCDs, which are called GFCIs in North America, were commonly used there many years before they were used in the UK.  Both consumer unit DIN rail compatible versions of RCD called RCCB and RCBOs are now mandatory in all new installations and some retrofits. The use of the RCD technology in Europe/Globe in general has resulted in the prices plummeting for this technology.
  • AFDD technology appears to be thumpingly expensive as of writing this post in 2017.


The imminent rise of the AFDD in the UK

What are the new requirements?

What changes are there in IEC 60364-4-42 and since when has this change existed? 

Was the change to the standard unexpected? 

 link to resource page

The imminent rise of the AFDD in the UK

My original article about AFCIs must have been prophetic, as the word, "on the street," is that AFDD (Arc Fault Detection Device) will be introduced in a limited capacity in the coming release of IEE 18th edition (BS 76721).  As with the roll out of RCCB technology, I suspect this is the proverbial foot in the door, before it becomes mandatory in all new standard domestic circuits. I suspect this technology will first be pushed onto sensitive commercial/industrial properties , especially where fire would be most threatening to life and property.
  • There has been a steady, slow and gentle, convergence of wiring standards across the globe and two of the push factors for the UK are the European Harmonised directive HD 60364-4-42:2015 and the International Electrotechnical Commission document IEC 60364-4-42:2014.
  • It is still the prerogative of the national standards body whether they implement international or harmonised standards in their jurisdiction.  The UK uses the Institution of Electrical Engineers (IEE) as the organisation which oversee the British Standards.  It is these standards that are implemented within the UK and subsequently many affiliated bodies in different parts of the world who also use the British Standards model.
  • Please note that the exact numbers of the International Electrotechnical Commission (IEC) and European Harmonised Directive (HD) documents/revisions may be inaccurate. Sadly, I am unwilling to spend literally hundreds of pounds to find out something that should be in the public domain anyway.

It is clear that that the big manufacturers of "fuse box/breaker box/consumer unit apparel" have read the writing on the wall and have positioned themselves for the imminent roll out of this technology.  I have included some of their material below and have added some further reading in my references page, which can be found in the link at the end of this post.

For some years Siemens have had a DIN rail compatible AFD unit in circulation within Germany.  Theoretically, this unit is already capable of fitting into a UK consumer unit and I've included the video below.  This video was actually in my original post and I think it is still worthy of a watch.
  • The acronym "DIN" as in "DIN rail" stands for, "Deutsches Institut für Normung."  Translated it means, "German Institute for Standardisation."  
  • The DIN rail configuration is widely used throughout Europe and much of the world.  Sadly the standard has left a lot of wiggle room for manufacturers to make their devices incompatible even within their own product ranges.  This is why I use the phrase "theoretically."

Interestingly, I have discovered that this Arc Fault technology is already widespread around the counties comprising Europe. Here's a quote from a the brochure/documentation of the European arm of an American company called "Eaton" :

European countries typically follow the HD 60364-4-42 harmonisation document and implement this standard in their national regulation and standardisation framework.

Many countries such as the Netherlands, the Czech Republic, Spain, Denmark, Latvia, Slovakia, Romania, Hungary and Switzerland have already implemented this novel protection against thermal hazards, while the implementation in Finland, Sweden, Iceland and Italy is currently ongoing.

This is a devastatingly cool video from "Eaton's European arm." It shows a masterclass in non-verbal instructions on the usage and implementation of their AFDD. The unit demonstrated is a combination module offering RCD and MCB (effectively an RCBO) protection but with the useful ability to indicate which type of fault tripped it.  This feature is an invaluable diagnostic tool for fault finding.  Eaton EU also have a rather slick and informative glossy brochure, which I have quoted from throughout this post.

What are the new requirements?

Arc Fault Detection Devices (AFDDs) in accordance with IEC 62606 are now recommended in final circuits such as:
• In premises with sleeping accommodations: e.g. hotels and hostels, daycare centres for children, nurseries, facilities that care for the elderly and sick, schools, residential buildings and apartments
• In locations with risks of fire due to the nature of processed or stored materials: e.g. barns, wood-working shops, stores of combustible materials, paper and textile processing factories, agricultural premises
• In locations with buildings combustible materials: e.g. wooden buildings, where the majority of the constructional material is combustible
• In fire propagating structures: e.g. high-rise buildings, forced ventilation systems
• In locations with endangering of irreplaceable goods: e.g. museums, national monuments, public premises and important infrastructure such as airports and train stations

Here's Siemens' video, which I previously posted in another post.  I'm sure the quality and design of  Eaton's video was greatly inspired by this one. Similar to Eaton's (EU) video, this has slick production values and graphics to match.

Their 5SM6 is referred to as an AFD and has been in service for many years.  Hopefully, Siemens will have used their field experience to ensure reliability and resistance to false tripping of their product.  I suspect their AFD will be soon be renamed an AFDD
  •  Personally I would really have a preference for name of AFCB as the UK implementation of AFDDs. This would only be to maintain consistency in the naming of domestic consumer unit furniture.

What changes are there in IEC 60364-4-42 and since when has this change existed?

Extract taken from the Eaton EU's Brochure:
In comparison with the edition from 2010, in Amendment 1 of 60364-4-42 significant changes were made in November 2014. These are, amongst others:

a) inclusion of additional requirements for automatic disconnection in cases of dangerous arcs with arc fault detection devices (AFDDs);

b) inclusion of an informative Appendix A for arc fault detection devices (AFDDs).

 These changes have been effective since 13th November 2014.

Interestingly, I have found another video with an impressive demonstration of a standard 40A type B MCB vs an 40A AFDD. Western Automation with another DIN rail compatible device suitable to be fitted in a UK style consumer unit.

Personally, I am not familiar with Western Automation as a brand but their website suggests they're an established research and development facility. I will explain below why I am not entirely convinced that this video is an accurate portrayal of what could happen in a UK wiring setup.

It would be interesting to see an RCCB in the same scenario.  It was not clear whether this was, what can be "loosely" termed, a "serial" or "parallel" arc.

Flames and hot gasses/plasmas provide a low resistance, conductive path between conductors.  I would expect a 30ma RCCB to work well before any major flames were produced.  In fact the 100ma rated RCCB is specified with that very purpose in mind. For an RCCB to successfully trip you would need to make several assumptions:

  1. An internal earth wire is fitted and connected to the faulty cable. or

  2. External earth plane such a conduit or earthed "extraneous" metalwork such as pipework or building structure. or

  3. There is a path to a different final circuit/ring main, not protected by the same RCCB, which would allow an imbalance in the live and neutral currents the RCCB is capable of monitoring. In this scenario that associated circuit would also need to have been compromised electrically.

If the scenario were say; a class II cable (no earth wire fitted) and the cable was sitting on a polyester rug, then an RCCB would not provide protection against the initial ignition.
  • A cable for a class II product does not require an earth conductor fitted or what UK electricians know formally as a Circuit Protective Conductor (CPC).
  • A class II cable normally only contains the conductors for both the live and neutral.  Live is what UK electricians know formally as Line.
  • A ring main is what UK electricians know formally as a low voltage, ring final circuit.
  • Low Voltage is considered by UK electricians as 230Vrms for single phase and 415Vrms for 3 phase.
  • My post was not really written with professional UK electrical technicians/engineers in mind but more a starting point for those who are interested in this topic.
Looking carefully at the video, it does look like a class II cable suspended in free air. If this were in the UK, then the cable would be fitted with a BS 1362 rated fuse in the plug or fused outlet.  If this cable were protected by a 3A cartridge fuse I would expect it to be likely to blow with a current draw between 9 ~ 40 A.   But if only protected by a type B, 40A, MCB, I would expect it to disconnect with a current draw in the region of  200 A.  In both cases the figures represent the current draw needed for a 20 milliseconds disconnection time. 
  • Just to put that into perspective a 13A cartridge fuse (BS 1362) would  need to draw a current between 80 ~ 230A for it to blow in the time frame of 20ms.  
  • 20ms is the time of one mains cycle of at 50Hz

My suspicion is that a physical cable catching fire is not as likely as a much lower key serial arc, ballasted by an attached appliance, setting something else on fire. So I would be slightly suspicious of that video being an entirely fair representation, but clearly it does show the feature and advantage of an AFDD in their particular demonstrated setup.

Was the change to the standard unexpected?

Extract taken from the Eaton EU's Brochure:
The approach to apply and recommend AFDDs with respect to IEC 60364-4-42 was not unexpected. Up to that time, no protective device being able to detect and effectively disconnect serial arc faults was identified in IEC 60364, i.e. no device having the capability to significantly lower the risk of electrically ignited fire hazards was mentioned. Although the AFDD product standard was publication of in 2013 and first products were available since 2012, the 2014 released IEC 60364 series is the first standard for low voltage electric installation which actively recommends the AFDD.

  • If you're not sure what a serial arc is then see my previous post on AFCIs

The fact that there are now at least four products out there is only the start, as simply being able to fit onto a domestic consumer unit's DIN Rail isn't enough for universal UK consumer unit compatibility. Especially if the consumer unit is already populated with circuit breakers.  Although all components known as domestic British circuit breakers, must fit a DIN  rail, sadly whoever was compiling the regulations forgot to make the busbar positions in a consumer unit also mandatory.  Consequently there are literally dozens of competing incompatible designs of domestic consumer unit fitted circuit breakers.

I have three videos of three implementations of AFDDs above.  The fourth is from Schneider but they don't appear to have a developed their information regarding their implementation at time of writing this post.  They do have a website and blog articles about AFDDs and I have included these in my further reading an resource page.

For further reading and references: Please read my resource page.

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