ArcFault Detection Devices

How does an AFDD work?

An AFDD detects the characteristics of dangerous arcing. Once it has been detected, it opens the electrical circuit to prevent a fire propagation. This is through an electronic system, that monitors electrical parameters in real time (current, voltage, frequencies etc).

What is a dangerous electric arc?

An electric arc becomes dangerous when it’s in an unexpected place of an electrical circuit; such as degraded cables and connections. In these places, it can ignite nearby materials, especially electrical insulators.

Do I need a separate AFDD for each circuit?

As per AS/NZS 3000:2018, AFDD should be installed after the main switch, located at the switch-board from which the final sub circuit being protected originates and at the origin of the circuit to be protected. Therefore, having a separate AFDD is required for each final sub-circuit.

Can an AFDD be installed on a circuit already protected by a Residual Current Device?

Yes. AFDDs are complementary protection to earth leakage protection and does not disturb it. When AFDD is embedding with earth leakage protection, the same rules have to be applied as RCBOs.

What are the main causes of arc fault detection device (AFDD) tripping?

If an AFDD has tripped because of its electronic monitoring (Both VISI-TRIP windows indicators are red), it is generally for one of the following reasons:

• Unbalanced current between phase and neutral, due to the neutral cable (connected to the AFDD), not corresponding to the phase (neutral crossing another circuit)
• Arc between conductors (phase and neutral / phase and PE)
• Arc on the same conductor (loose contact in a cable or a connection)
• Earth leakage current
• Network overvoltage (neutral break)

Is there any equipment to test that AFDD are functioning properly?

No. The test button is the only way to test if an AFDD is functioning properly.

On which circuits should we install AFDDs?

AFDDs are designed to protect residential and commercial electrical installations. It is highly recommended for power (socket outlet) circuits, due to potential:

• Arcing in extension boards
• Damage to cables plugged into socket outlets behind furniture (sofas)
• Damage to extension leads due to bending around corners or under furniture
• Damage to plugged cables due to temperature variation, ultraviolet rays, vibrations, humidity, and rodents in outdoor environment.

You should also consider lighting and other circuits in the following applications:

• Premises with children, handicapped or elderly people; as they might take longer to evacuate in case of fire.
• Premises constructed with combustible materials e.g. wooden buildings that might not allow enough time to evacuate.
• Premises with high risk of fire due to the nature of processed or store goods like a business storing large amounts of paper, wooden or other combustible materials.
• Irreplaceable goods stored on premise.

Why is traditional electrical protection (through devices such as MCB or RCD) not enough to manage the risk of electrical fires?

MCBs and fuses protect against overload or short circuits. Earth leakage protection device (RCD) protects against current flowing into earth. Both cases may generate electrical arcs and create fires, hence they can’t be over-looked.

However, some dangerous arc faults may remain invisible to MCBs and RCDs due to their low current value. It could be too late by the time traditional devices detect the fault. Therefore, it is important to have an AFDD device installed to help detect arc faults at a much earlier stage.