AFDD !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

[Toneyz]

Sorry I don't know how to post up a youtube link but have a look at the John Ward one part 2 on AFDD's worth a watch.

 

[netblindpaul]

Just to put it into context, if it was a 32A AFDD then it would be about 5A

I know, I have access to the standard.
I used 2.5, because it is, the, minimum detection level in the standard.
I took this up with “the industry” at Elex Alexandra Palace in 2018, I took this up with the IET just after the DPC for the 18th was published, outside my comments on said DPC.
There have been no explanatons, answers to my concerns, nor justifications forthcoming from the IET, nor the manufacturers.

 

[Deleted member 26818]

Yes, 30mA RCDs detect imbalances between Line and Neutral, not loose terminals or broken conductors.
RCDs have lower current threshold because they are intended to prevent electrocution.
AFDDs on the other hand are intended to prevent fires.

 

[netblindpaul]

Don't forget, I mentioned nothing about additional protection by RCD, i.e. a 30mA device, I was referring to 0.3A devices, 300mA, for prevention of fire, as per BS7671 clause 422.3.9.

 

[netblindpaul]

J.W. has just posted the third video with an electric heater and it still did not trip. RCD's are ok for faults to earth not sure regarding L-N and broken conductors. Look forward to the replies.

You are correct, in that RCD's do not protect against series faults, such as broken conductors, we have MCB's to protect against L-N faults.
However my issue is that we are only allowed the energy from a 300mA device in a parallel arc from L-E, but, 2.5A minimum in a series arc...

 

[Deleted member 26818]

Don't forget, I mentioned nothing about additional protection by RCD, i.e. a 30mA device, I was referring to 0.3A devices, 300mA, for prevention of fire, as per BS7671 clause 422.3.9.

A 300mA RCD is not going to trip in the event of a fire, until the cables have melted enough, to allow earth leakage to occur.

 

[netblindpaul]

Well, tell JPEL 64 that then because they require it, and they are allowing a MUCH greater energy with an SFDD to melt the cables and start a fire, so it is somewhy hypocritical & contradictory of them.
Mind that’s not new, but it is also not of my doing.

 

[Shoei]

The manufacturers don't specify how AFDDs detect arcs but you can get a good idea from patents in the public domain. (one attached). The trip algorithms are quite specific in an attempt to separate dangerous arcing from (say) a spot of welding or a sluggish fridge thermostat. This is a problem, wiring has evolved to the needs of each territory - in the US the key concern has always been stopping fires from their high-current radials in wooden buildings. In the UK the priority is protection against shock from the higher voltage, with arc-related fires less common in RFCs in brick buildings. If AFDDs are optimised for the US then they aren't optimised for the UK.

I'm not aware of any research projecting the 'benefit' of AFDDs in the UK and it's possible the benefits are negative. If we are obliged to give up the inherent fault tolerance of RFCs to make AFDDs work then their adoption may increase the incidence of fires, especially considering the higher flammability of UK PVC insulation compared to US (UL certified) wiring.

It could go either way but until some proper research is published showing that UK fire risk would be reduced by the introduction of AFDDs I wouldn't go near one.

 

[GBDamo]

It's easy to make people believe rubbish, when they don't like thinks in the first place. It falls into their beliefs.

Confirmation bias they call it.

 

[Nigel]

I can't take the credit for this @essex as it was a mate at work that pointed it out to me. I was initially a sheep, like most, who believed that the AFDD's should be detecting most arks.
As @netblindpaul has pointed out "If, the maximum fault energy to cause a fire is required to be limited by an RCD to 0.3^2 x t, then why is it allowed to be 2.5^2 x t for an AFDD?"
I presume it's down to cost. When you look at how the AFDD's detect arks then if they were to detect 30mA then there is going to be lots of nuisance tripping, unless the detection device is more fine tuned. This will increase the cost of these even more.

Matbe it is because RCDs are already in place currently for most high-risk circuits so no need to replicate.