What is an AFCI?

Arc-fault circuit interrupters (AFCIs) are special types of receptacles (outlets) and breakers that are designed to detect arcs in home wiring circuits.

How do they Function

AFCI’s monitor the electrical waveform, if a dangerous arc occurs the AFCI will open (interrupt) the circuit thus cutting the power to the circuit to prevent fires from occurring. AFCI’s are also capable of detecting safe arcs such as happen when a switch is turned on or an appliance plug is removed from a receptacle.

What is an Arc?

When electrical current passes an air gap from an energized component to a grounded component an Arc occurs. Arcs produced by home wiring create high levels of heat that can ignite the surrounding materials and lead to structure fires.

According to the National Fire Protection Association (NFPA) between 2015 and 2019 there were an average of 346,800 home structure fires per year. These fires caused an annual average of 2,620 civilian deaths; 11,070 civilian fire injuries; and $7.3 billion in direct property damage. 9% of these fires were caused by electrical distribution and lighting equipment.

Where are the common areas that arcs form?

Arcs can form at improperly connected conductors or where the wiring insulation has become brittle and has been damaged. Bare conductors increases the chances for arcing to occur. The following are areas that are common causes for arcing:

  • electrical cords damaged or trapped beneath furniture or doors.
  • damage to wire (conductor) insulation from nails or screws driven through walls.
  • appliance cords damaged by heat, natural aging, kinking, impact or over-extension.
  • spillage of liquid.
  • loose conductor (wiring) connections in receptacles, switches and light fixtures.

To clarify, building standards define an outlet as: “A point on the wiring system at which current is taken to supply equipment that utilizes electric energy.” So, an outlet can be a light, smoke alarm or a receptacle, etc. Many people somewhat mistakenly call receptacles “outlets”…

Where are AFCI’S required?

In Wisconsin as of this writing AFCI protection is required at the following locations:

Family Rooms, Dining Rooms, Living Rooms, Parlors, Libraries, Dens, Sunrooms, Recreation Rooms, Bedrooms, Closets, Hallways and Similar Rooms or Areas AND Laundry Areas. As of this writing in Wisconsin Kitchens are not included in this requirement.

There are two ways to protect these circuits, AFCI breakers can be installed at the electrical panelboard or AFCI receptacles (outlets) can be installed to protect these areas. There are a few other rules but the important part is that these areas are protected to prevent fires. If you live in an older home upgrading to AFCI protected circuits may be a good safety upgrade.

A note on the difference between AFCI’s and GFCI’s

Ground fault circuit interrupters are installed to prevent electrical shock. A GFCI measures the current at the receptacle between the hot and neutral conductors, if this varies by 5 milliamps or more the device trips. This is usually caused by a short in the appliance being used. GFCI’s are also installed in older homes where there is not an equipment ground.

So, GFCIs are intended to prevent personal injury due to electric shock, while AFCIs prevent personal injury and property damage due to structure fires.

As always, I hope you took some value from this post and if you have any home related questions, please let me know at the email address below.



Aaron M. Zuehlke is the owner and inspector at Zuehlke Inspection Service, LLC, a full-service home inspection company serving Southern Wisconsin. Specializing in Home inspection, Radon Testing, Mold Testing/inspection, Residential Thermal Imaging, and Manufactured Home Foundation Certifications. He also manages several rental properties through Zuehlke Properties, LLC. He can be reached by email at Aaron@Zuehlkeinspections.com or by calling the office at 608-931-7485.

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