AFDDs – A life saver or an unnecessary cost?Spencer Yates
Arc Fault Detections Devices introduced themselves in BS7671 – 18th Edition (The Wiring Regulations) back in 2018 where they were recommended for use in applications such as locations with a risk of fire due to the nature of processed or stored materials; locations with combustible constructional materials; fire propagating structures and locations with endangering of irreplaceable goods.
As electricity continues to be a major contributor to accidental fires within UK dwellings with over 17,000 recorded each year, with around 12% of these attributable to the electrical installation; upcoming changes to these regulations will see the introduction of AFDDs as a mandatory requirement for specific installations.
Either as a stand-alone device or one combined with an MCB or RCBO, the AFDD looks to isolate a circuit at risk of fire caused by arcing within the cables or equipment. Our range of AFD Devices are combined with an RCBO and look at three key elements when tripping in the event of an arc fault:
(a) a current magnitude greater than 2.5 Amps;
(b) a minimum time of the arcing event (>100ms) and
(c) the presence of hi-lo asymmetrical frequency components on the circuit.
The combination of all three of these elements will trigger the device and fully isolate the circuit using its double pole switching format. The microprocessor within the device has been pre-programmed with a vast array of arc fault signatures, so the device knows how to differentiate between what’s a genuine arc event to that of a true arc fault. They can also identify between a series arc fault (in one conductor) and a parallel arc fault (between two phase conductors).
Series Arc Fault
Parallel Arc Fault
Like with all new technology, change can lead to unexpected results. One of those being raised is the increase in material costs. Development of our AFDD technology has been ongoing for the past 4 years to ensure production of a device that is stable within an installation and does not nuisance trip due to over-sensitivity. However, the benefits of high performance AFDDs – protection of electrical installations from fires – can far outweigh the increase in costs in the event of a genuine fault.
Another unexpected result could be the introduction of an AFDD to an existing circuit – one that’s not tripped before – and suddenly starts to trip. The LED status indicator suggests there’s a parallel arc fault and after a check of the circuit, a damaged cable is found and arcing present between the phase and neutral conductors. When protected by an MCB, RCD or RCBO, this fault may have gone unnoticed until it manifests in to something potentially more dangerous. This is due to the current magnitude of the fault potentially being too low for these devices to trigger. The AFDD however would identify this fault and isolate the circuit safely.
AFDDs combined with RCBOs offer the greatest level of protection currently available – offering Overcurrent, Short Circuit, Earth Fault and Arc Fault protection in one device. Their requirement in the near future in higher risk residential dwellings will undoubtedly provide a safer environment and ultimately, protect lives.
For further details on our range of Arc Fault Detection Devices, please visit: