Arc Fault Detection Devices

What are arcs?

Arcs are visible plasma discharges caused by electrical current passing through a normally nonconductive medium, such as, air. This is caused when the electrical current ionizes gases in the air, temperatures created by arcing can exceed 6000 °C. These temperatures are sufficient to start a fire.

What causes arcs?

An arc is created when the electrical current jumps the gap between two conductive materials. The most common causes of arcs include, worn contacts in electrical equipment, damage to insulation, break in a cable and loose connections, to mention a few.

Why would my cable be damaged and why would there be loose terminations?

The root causes for cable damage are extremely varied, some of the more common causes of damage are: rodent damage, cables being crushed or trapped and poorly handled and damage to the insulation of the cable caused by nails or screws and drills.

Loose connections, as previously stated, occur most commonly in screwed terminations, there are two main reasons for this; the first is incorrect tightening of the connection in the first place, with the best will in the world human beings are human beings and make mistakes. Whilst the introduction of torque screwdrivers into the electrical installation world has improved this considerably mistakes can still happen.

The second way loose terminations can occur is because of the electro motive force generated by the flow of electricity through conductors. This force over time will gradually cause connections to loosen.

What are Arc Fault Detection Devices?

AFDDs are protective devices installed in consumer units to provide protection from arc faults. They use microprocessor technology to analyse the waveform of the electricity being used to detect any unusual signatures which would signify an arc on the circuit. This will cut off power to the affected circuit and could prevent a fire. They are far more sensitive to arcs than conventional circuit protective devices.

Do I need to install Arc Fault Detection Devices?

AFDDs are worth consideration if there is an increased risk of fire, such as:

• Premises with sleeping accommodation, for example houses, hotels, and hostels.

• Locations with a risk of fire due to the nature of processed or stored materials, for example stores of combustible materials.

• Locations with combustible constructional materials, for example wooden buildings.

• Fire propagating structures, for example thatched buildings and timber framed buildings.

• Locations with endangering of irreplaceable goods, for example museums, listed buildings and items with sentimental value.

Do I need to install an AFDD on every circuit?

In some cases, it may be appropriate to protect particular final circuits and not others but if the risk is due to fire propagating structures, for example, a timber framed building, the whole installation should be protected.