arc-fault circuit interrupter [AFCI]

In by Mark Goodman

A device intended to provide protection from the effects of arc faults by recognizing characteristics unique to arcing and functioning to de-energize the circuit when an arc fault is detected.

arc-fault circuit interrupter (Wikipedia)
This AFCI (the circuit breaker with the yellow label) is an older generation AFCI circuit breaker. The current (as of 2013) devices are referred to as "combination type" and usually appear with a green label.

An arc-fault circuit interrupter (AFCI) also known as an arc-fault detection device (AFDD) is a circuit breaker that breaks the circuit when it detects an electric arc in the circuit it protects to prevent electrical 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).

AFCI breakers have been required for circuits feeding electrical outlets in residential bedrooms by the electrical codes of Canada and the United States since the beginning of the 21st century; the U.S. National Electrical Code has required them to protect most residential outlets since 2014, and the Canadian Electrical Code has since 2015. In parts of the world using 230 V, where the higher voltage implies lower currents, specifically Western Europe and the UK, adoption is slower, and their use is optional, except in high risk cases.

In the USA, arc faults are one of the leading causes for residential electrical fires. 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.

Conventional circuit breakers only respond to overloads and short circuits, so they do not protect against arcing conditions that produce erratic, and often reduced current. An AFCI is selective so that normal arcs do not cause it to trip. 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.

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