The Arc Fault Detection Device… again.

mapj1:

Funny I often end up going to bed with my dishwasher etc, but then we are married.?

Careful what you "go to bed" with!

Colin Jenkins:

Hello Everyone.

A very interesting thread.  For my family, I did a risk assessment with respect to the omission of AFDDs for our property when I replaced our consumer unit last year.  I've attached it here for information only as it reflects many of the discussion points that have been raised.  Just after I completed the CU change, Wylex released the single-module RCBO, so the point about changing to a duplex unit is no longer valid, but it certainly applied at the time.


Another aspect that came up in the Youtube videoes is that RCBO/AFDDs draw app. 1 Watt each continually.  That adds up to an unwelcome rise in temperature when a row of these are stacked side by side in a metal enclosure.

Regards,

           Colin Jenkins.Hilltop Cottage - omission of AFDDs Annonimised.docx

Just an observation/correction, if I've read it correctly, you're saying that affds won't detect arcs in the ring final ccts but will in the spur connected to the ring, but note that according to Hager*, parallel arcs are detected in rings, but serial arcs are not.

*https://hager.com/uk/support/regulations-18th-edition/arc-fault-detection-devices


On a different note, I get perhaps the erroneous impression from your Ax that there's a sense of overreliance on the ccts being 'monitored' by the rcd's which somehow minimises the need for afdds despite recognition in the preamble that they do different things. Cost aside, perhaps it's safer to install afdds than not.


Also, while the property may be occupied, and things turned off when people are out, there was apparently no factoring in of e.g. rodent damage in lofts or under floors, or of inspection and testing at regular intervals, which may be more frequent if in regular use, thereby detecting things like loose connections which can't be detected by home users. So perhaps afdds may help where inspections are few and far between - if they actually work as billed/intended of course.

davezawadi (David Stone):

The eye is not bad at seeing significant trends Mike, isn't it? Assuming about 10% of installs have been replaced in the last 12 years we should see a trend, I don't. Yes when every installation has AFDDs it might go back to the already improving trend line, this is just the increasing safety of electrics of all kinds. The "noise" (randomness of this kind of data) is certainly bigger than any possible signal of improvement, the trend from "unknown" cause is much greater than the AFDD one.

Fires caused by faulty appliances in domestic dwelling houses tend to be from causes which an AFDD is not likely to prevent. For instance, fires in tumble driers from build-ups of fluff (see for instance this local news report from 2019: https://westbridgfordwire.com/fire-service-issues-warning-after-tumble-dryer-fires-in-nottingham/). 


Fires in electrical appliances are a significant but relatively small proportion of the total number of dwelling fires each year. I recently retired as the performance manager for Scottish Fire and Rescue, and was responsible for the publication of the Service's annual fire statistics (available if you are interested from https://www.firescotland.gov.uk/about-us/fire-and-rescue-statistics.aspx). Fire statistics in England, Wales and Scotland are based on data recorded on the National Incident Recording System by crews that attended the incidents, and represent what they found at the time. Accordingly, you won't necessarily be able to make deductions about arcing as a cause from the published statistics. Leaving aside obvious cases such as burnt out shower isolating switches, only detailed fire investigation work would be able to determine in many cases if arcing of some kind contributed to the fire. Fire investigation is a specialist activity undertaken after major fires or any in which there was loss of life, and an appliance fire limited to the room of origin in which no major injuries or fatalities arose would not normally need the services of a fire investigation team. 


All fire services look for trends in causal factors found by fire investigators to see if there is a common cause which needs action nationally. London Fire Brigade for instance spotted failures in LEC fridge-freezers (fires caused by spark-suppression capacitors failing if I remember correctly), and the Whirlpool tumble drier failures which have caused hundreds of fires nationally.


I doubt very much that AFDDs will make a significant improvement in fire safety. Over 60% of dwelling fires start in the kitchen and result from human factors - leaving pans unattended and so on. All fire services conduct home fire safety visits and try their best to advise homeowners on issues such as overloaded sockets, poor use of trailing power leads and so on. From what I've seen in the incident logs for fires where electrical supply or electrical appliances were involved, AFDDs would have been unlikely to have made much of a contribution. To give an example, AFDDs protecting an RFC would not do much to help stop the major fires that have occurred from criminal interference with meter tails to power the heating used for cannabis farms!


-Stewart