Arc Fault Detection Devices

So far this year, 8919 (17% of all) fires have been caused by faulty appliances and leads in England. Following on from the tragedy at Grenfell Tower in 2017 the government has ramped up measures to prevent domestic fires. Due to this increased awareness for fire safety we have been receiving more and more enquiries about AFDDs (Arc Fault Detection Devices). In this blog we will try to shine a light on what AFDDs are and how they work.

Currently in most domestic distribution configurations there are four layers of protection to the end user:

  1. Protection provided by the cover of consumer units- shielding of any live terminals
  2. Overcurrent protection from MCBs
  3. Earth leakage protection from RCDs up to 30mA- detecting signs of electric shock in humans
  4. Overvoltage protection from surge arrestors

By adding an AFDD to a circuit you are adding a fifth layer of protection to it, protecting the circuit from arc faults.

So, what is an Arc?

An Arc in as simple of terms as possible is a flash of energy between two live terminals, a perfect example of an arc is a taser. In the case of a taser the arc is deliberate and controlled, in the case of your extension lead for your phone charger an arc is not deliberate and not controlled. An AFDD in a circuit can prevent arc faults before they burn through the insulating plastic in your home and start a fire, arcs can generate temperatures of 6000 °C. Here are some common causes of arc faults in the home:

  • Damaged or crushed cables
  • Cables with worn insulation (over-bending or stretching)
  • Loose terminals (Screws not set to manufacturers guidelines for torque)


How do AFDDs work?

Using the latest technology to detect the waveform of an arc fault. An arc fault has a specific waveform that passes through the circuit to the AFDD. Which will then detect this waveform and cut off the circuit, preventing further arcing. An RCBO or an MCB will not be able to pick up on this waveform so without an AFDD the arc would continue to form and could cause a fire.

Currently AFDDs must be installed at the origin of the final circuits that are being protected, meaning they will be taking up more room in your consumer unit. As time goes on manufactures will hopefully start to release MCBs/RCBOs with Arc Fault Detection incorporated in. This would greatly reduce the amount of space required in consumer units.

Northern Switchgear  currently supply Schneider Electric’s Acti9 AFDD. Take a minute to watch this short video from Schneider about AFDDs.




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