Arc-fault circuit interrupter

An arc-fault circuit interrupter (AFCI) or arc-fault detection device (AFDD)^[1] 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. An AFCI 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).

In Canada and the United States, AFCI breakers have been required by the electrical codes for circuits feeding electrical outlets in residential bedrooms since the beginning of the 21st century; the US National Electrical Code has required them to protect most residential outlets since 2014,^[2] and the Canadian Electrical Code has since 2015.^[3]

In regions using 230 V, the combination of higher voltage and lower load currents lead to different conditions being required to initiate an arc fault that does not either burn clear or weld to a short circuit after a short time, and there are different arc characteristics once struck. Because of this, in Western Europe (where in many countries a domestic supply may be 400V 3 phase) and the UK (where domestically a single phase 230V supply is common), adoption is slower, and their use is optional, only being mandated in specified high risk locations. The Australian and New Zealand regulations – Wiring Rules (AS NZS 3000:2018) do not require installation of AFDDs in Australia. However, in New Zealand all final sub-circuits with ratings up to 20 A will require protection by an AFDD if they supply locations with significant fire risk, locations containing irreplaceable items, certain historic buildings, and socket-outlets in school sleeping accommodation.^[4] Most sockets in these countries are on circuits rated at 20 A or less.

In the US, arc faults are said to be one of the leading causes for residential electrical fires.^[5] Each year in the United States, over 40,000 fires are attributed to home electrical wiring. These fires result in over 350 deaths and over 1,400 injuries each year.^[6]

Conventional circuit breakers respond only to overloads and short circuits, so they do not protect against arcing conditions that produce erratic, and often reduced current. AFCIs are devices designed to protect against fires caused by arcing faults in the home electrical wiring. The AFCI circuitry continuously monitors the current and discriminates between normal and unwanted arcing conditions. Once detected, the AFCI opens its internal contacts, thus de-energizing the circuit and reducing the potential for a fire to occur.^[7]