Operating principle and types of AFCIs
– AFCIs detect electrical current associated with wire arcing.
– They provide protection against parallel arcing, series arcing, ground arcing, overload, and short circuit.
– AFCIs open the circuit if dangerous arcing is detected.
– Combination AFCI breakers and AFCI receptacles are available.
– AFCI receptacles provide series arc protection for the entire branch circuit.
Electrical code requirements
– AFCIs have been required in circuits feeding outlets in residential bedrooms since the early 2000s.
– AFCI protection is now required in various areas of dwelling units, including kitchens, family rooms, and hallways.
– AFCI protection can be achieved through combination type breakers or AFCI receptacles.
– Not all U.S. jurisdictions have adopted AFCI requirements, so local codes should be checked.
– The UK Wiring Regulations mention arc fault devices for designs with a high risk of fire from arc faults.
– The German Wiring rules recommend AFDDs for high-risk situations.
Fire statistics and safety impact
– Arc faults are one of the leading causes of residential electrical fires in the U.S.
– Over 40,000 fires are attributed to home electrical wiring each year in the U.S.
– These fires result in over 350 deaths and over 1,400 injuries annually.
– Conventional circuit breakers do not protect against arcing conditions.
– AFCIs reduce the potential for fires by opening the circuit when unwanted arcing is detected.
Limitations of AFCIs
– AFCIs can indicate false positives by identifying normal circuit behaviors as arc faults.
– Lightning strikes can resemble arc faults, leading to nuisance tripping of AFCIs.
– Vacuum cleaners and some laser printers can also trip AFCIs, reducing their overall effectiveness.
– AFCIs do not provide specific protection against glowing connections, high line voltages, or low line voltages.
– Sensitivities and mitigation of AFCIs to radio frequency energy have been known since 2013.
Interference and additional information
– AFCIs may interfere with the operation of some power line communication technologies.
– AFCIs do not detect high line voltage caused by an open neutral in a multiwire branch circuit.
– AFCIs do not detect low line voltage, which can cause electromechanical relays to repeatedly turn off and on, leading to fires.
– DIN VDE 0100-420 provides protection against thermal effects in low voltage electrical installations.
– Interference issues with power line communication technologies have been addressed by the ARRL (American Radio Relay League) and manufacturers. Source: https://en.wikipedia.org/wiki/AFDD
An arc-fault circuit interrupter (AFCI) or arc-fault detection device (AFDD) 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, and the Canadian Electrical Code has since 2015.
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. Most sockets in these countries are on circuits rated at 20A or less.
Most of the rest of the 230V world does not consider AFDDs to be a priority currently.
In the US, arc faults are said to be 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 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.
