AFDD new safety feature ? or needless complication?

[adam2]

The latest edition of the wiring regulations contains a "recommendation" but not a requirement, that new electrical installations be equipped with Arc Fault Detecting Devices, AFDDs.

In theory this would provide enhanced safety since such devices detect an "arcing fault" such as a loose or intermittent connection that could start a fire.
These devices have been widespread in new installations in the USA, were they are known as AFCI, Arc fault Circuit Interrupts.

Reports from the USA are mixed as to the usefulness of the devices in practice. It is frequently alleged in the USA that the requirement for these devices was driven by manufacturers seeking a new profit opportunity.

They certainly add another layer of cost and complexity and opportunities for nuisance tripping. They are for example liable to trip due to arcing at switch contacts and in brush type motors.

I presume that they cant be used to supply arc welders ! or arc lamps

At present AFDD are only recommended, not required, but this years recommendation tends to be next years requirement.
And in anything publicly funded, a recommendation is in effect a requirement.

[Mr. Fox]

Heh... one per circuit @ ~£120 a pop! Smallest available (Crabtree) is 2 units wide, so let's factor in a new (double decker) consumer unit, while we're at it.

I'm told they won't trip on brushed motors/switch arcing, as the little computer inside is far too intelligent to allow that to happen - I'm not convinced of how intelligent it is to allow a little computer to control everything in the first place.

Hopefully Big Clive will disembowel one of the units soon, so we can make our own judgement.

[BritDownUnder]

I don't think there is a standard in Australia but we have specified some of those detection units in larger higher fault level industrial units but they are unknown in domestic applications.
Over here some use optical fibres inside an electrical cabinet to detect the intense light and can also use a current detector to look at simultaneous current rise before activating. I spent a few years doing Arc Flash calculations for mining customers and earned some nice money doing it. It was a good opportunity for me to collect some money off of large multinational companies for a while instead of the other way around.

I think this all arose out of insurers in the US wanting to reduce payouts for people injured when arc faults occur when racking out breakers and during switching from what I recall.