What is an AFDD and how does it work?

Why would I need an AFDD?

Each year over two million fires erupt all over Europe. More than one third of these are due to faults in the electrical installation which prevailingly occur as a result of dangerous arc faults. 

AFDD provides maximum safety in all buildings, thus protecting people and valuable assets. By early detecting arc faults and disconnecting the affected circuit they offer reliable and complete protection in any type of building.

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.

Situation increasing risks of fire
Power supply cord subject to excessive force (By furniture or a position)	Power supply cord defective following inappropriate or excessively numerous operations	Cable weakened at connection	Accidental damage to a cable
Power sockets in poor condition	Ageing of cable protective devices	Loose connections	Cables are damaged by their environment: UV, vibrations, moisture, rodents.

What is an Arc Fault?

An electrical arc is created when electricity jumps between two conductive materials within a non-conductive medium, i.e.: air. In low current instances, this is just a quick, small spark. However, if the current is high enough, sufficient energy is emitted to generate and sustain a proper arc. 

In domestic wiring terms, an arc fault is where there is unintentional arcing in a circuit, allowing current to jump between two cable cores and can generate temperatures in excess of 6000°C - Plenty enough to start a fire.

This isn’t to say that all arcs must be prevented, lots of everyday pieces of electrical equipment produce an arc during their normal operation:

1. When you flick on a light switch in your home, a small electrical arc is generated between contacts. 

2. An electric drill will create arcs inside its motor when in use.  

What is an Arc Fault Detection Devices (AFDD)?

An arc-fault detection device (AFDD) or arc-fault circuit interrupter (AFCI) is a circuit breaker that breaks the circuit when it detects the electric arcs that are a signature of loose connections in home wiring. 

Loose connections, which can develop over time, can sometimes become hot enough to ignite house fires. 

What are the two types of arc fault an AFDD will detect?

An AFDD selectively distinguishes between a harmless arc (incidental to normal operation of switches, plugs, and brushed motors), and a potentially dangerous arc (that can occur, for example, in a lamp cord which has a broken conductor).

Where are arc fault detection devices installed?

AFDD can be 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.

Like a Residual Current Circuit Breaker (RCCB) or Residual Current Breaker with Overcurrent protection (RCBO), AFDD usually incorporates a test button which can be operated by the end-user to prove the mechanical operation of the device.

What types of circuits can AFDDs be used on?

The regulations state AC single-phase circuits not exceeding 230V, that includes ring circuits, radials etc.

Types of Arc Faults

Parallel arc faults are found with damage caused to insulation which allows current to flow between conductors, usually between phase and neutral.	Series arc faults are found in loose terminal connections, damaged cords or frayed/damaged conductors. These arcs are created in one conductor only, either phase or neutral.

How does it work?

The arc fault detection device technology makes it possible to detect dangerous arcs and thus protect installations. 

Such devices have been deployed successfully in the United States since the early 2000s, and their installation is required by the National Electric Code.

Since 2013, the IEC 62606 international standard defines Arc Fault Detection Devices (AFDD) which detect the presence of dangerous electric arcs and cut off the circuit’s power supply to prevent initiating the first flame.

According to IEC 62606, arc fault detection devices shall react very fast in case of arc faults and isolate the circuit within a limited time. These dangerous electric arcs are not detected by residual current devices nor by circuit breakers or fuses.
Speed is of the essence as an electrical arc can degrade in a flash (literally), igniting any nearby inflammable material and causing a fire. 

MCB vs AFDD tripping curve

AFDD as a single device, including an arc fault detection unit and opening means and intended to be installed in series with a protective device, that can be a MCB or RCBO.

AFD unit with opening means installed in series with an RCBO

AFDD as one single device, including an arc fault detection unit and a protective device such as a MCB or RCBO.

AFD unit with MCB

Do I need to install Arc Fault Detection Devices (AFDD)?

Arc Fault Detection Devices are designed to limit fire risks caused by the presence of arc fault currents in the final circuits of a fixed installation. They are installed in electrical switchboards, to protect circuits supplying power sockets and lighting and are especially recommended in cases of renovation.

Since 2014, International Standard IEC 60364 - Electrical installations of buildings Part 4-42 make the following recommendations surrounding the installation and application environments of AFDD in residential and commercial buildings:

1. In locations with sleeping accommodation (e.g., hotels, nursing homes, bedrooms in homes)

2. In locations with risks of fire due to high quantities of flammable materials (e.g., barns, wood-working shops, stores of combustible materials)

3. In locations with combustible construction materials (e.g., wooden buildings)

4. In fire propagating structures (e.g., high-rise buildings)

5. In locations where irreplaceable goods are housed (e.g., museums)

6. It is recommended that AFDDs be installed at the place of origin of the low voltage final circuit to be protected (i.e., switchboard of an electrical installation).

More specifically, the installation of the AFDD is highly recommended to protect circuits with the highest risk of fire, such as:

1. Protruding cables (risk of knocks)

2. Outside cables (greater risk of deterioration)

3. Unprotected cables in secluded areas (like storage rooms)

4. Aging, deteriorating wiring or wiring for which the connection boxes are inaccessible.

Currently, the cost of AFDD is relatively high, and you can decide whether to use the product in your existing circuit unit to ensure the safety of your property according to the actual situation.

Note: Parts of the article reference the Electrical Installation Wiki.