The 2011 edition of the National Electrical Code requires installation of AFCIs in new construction to protect against electrical fires on all electrical circuits that serve living areas of the home. Living areas are defined as everything other than kitchens, bathrooms, garages, laundry rooms and house exteriors. These “non-living” areas must have ground fault circuit interrupters to protect against electrocution but as of 2013 were not required by the NEC to also have AFCI protection against electrical fires.
Arc faults in residential electrical wiring permit electricity to jump through the air via an electric arc to an unintended path. An arc fault can heat electric wiring to extreme temperatures that can melt conductors and ignite anything combustible nearby. Arc faults can occur from loose connections, damaged insulation, crossed wires, or pinched or overheated wires. An arc-fault circuit interrupter or AFCI is required on certain circuits to protect against electrical fires by cutting power when arc faults occur.
A conventional circuit breaker isn’t sensitive enough to detect electricity arcing through the air while the arc is still too small to ignite a fire. An AFCI is a tiny electronic computer programmed by the manufacturer to look for the patterns of current spikes and voltage drops that distinguish harmless ordinary arcing, such as from an electric motor or light switch, from dangerous arcing that requires an immediate power cutoff.
Inspectors will write up as deficient a home that does not have Arc fault protection present but may also note if it was not required when the home was built.