The 18th Edition of the Wiring regulations is proposing that some circuits may require the fitting of an Arc Fault Detection Device (AFDD).
In this blog we describe what an AFDD is and what it does.
Conventional circuit breakers do not afford reliable protection against arc faults. That is because they are not designed to detect sudden dangerous arcs. They ensure protection against short circuits and overloads.
And even if you are careful to keep cords out of harm’s way and to use only certified plugs and adapters, arc fault conditions may build up out of sight. In all homes your power use alternates between periods of peak and standby consumption. Such patterns put a strain on cables and connections, wearing out the insulation and loosening wires. As a result, weak points form in your installation. That’s where electrical arcs occur. And you have no way of knowing. Until it’s too late. Unless, that is, you have an arc fault detection device.
What is an arc fault detection device?
Arc Fault Detection Devices (AFDDs) are devices that protect specifically against arc faults. They automatically trip a circuit when they detect dangerous electric arcs.
They are compact, modular devices that are easily installed in electrical panels along with other protective equipment. Each AFDD is designed to protect an electric circuit, instantly detecting any dangerous arc. You should install AFDDs on the electrical circuits most exposed to risk – e.g. the final circuits that supply socket outlets.
Can arc fault detection devices distinguish between dangerous and working arcs?
Yes. Arc fault detection devices are extremely sensitive and designed to sense and respond only to potentially dangerous arcs. They use a special algorithm to distinguish between dangerous and working arcs – i.e. the harmless sparks that you see when you flick a switch or pull a plug. This is important, as over-sensitive AFDDs could be prone to nuisance tripping – e.g. interrupting a circuit when it senses the slightest harmless arc.
How do arc fault circuit breakers work?
AFDDs constantly monitor and analyse patterns in electrical current and voltage waveforms. They are on the look-out for the random, non-predictable yet persistent patterns of waveform that denote a potentially dangerous arc. When it senses a potentially dangerous wave pattern, it trips, thus isolating the faulty circuit. An AFDD can work in conjunction with a “circuit-breaker” or residual-current circuit breaker with overload protection (RCBO). It may also incorporate its own switching function.
AFDDs react very fast to the slightest change in wave patterns. Speed is of the essence, as an electrical arc can degrade in a flash (literally), igniting any nearby inflammable material and causing a fire.
Example of AFDD
