What Are AFCIs?
Arc-fault circuit interrupters, or AFCIs, are special outlets or breakers that detect dangerous electrical arcs in home wiring. These devices protect against the risk of electrical fires by sensing changes in the electrical current’s waveform and stopping the circuit when needed.
How Do They Work?
AFCIs constantly monitor electrical currents and will “trip” or shut off the circuit if they detect an arc that could start a fire. Importantly, they know the difference between harmless arcs (like plugging in a device) and unsafe arcs that can ignite materials.
What is an Arc?
An arc is a glowing discharge that happens when electric current flows across a gap, like from a live wire to a grounded object. Even though a large arc (like lightning) can seem extreme, smaller arcs in homes can also create enough heat to start a fire.
Why AFCIs Are Important
According to 2005 statistics from the National Fire Protection Agency, electrical fires caused damage to about 20,900 homes, took 500 lives, and led to $862 million in property damage. Arcs are a major cause of these fires and often go unnoticed by traditional circuit breakers.
Where Do Arcs Form?
Arcs can form in places where wires or insulation are damaged. Older homes are particularly at risk as insulation can age, crack, or chip over time. Situations where arcs are more likely include:
- Cords damaged by vacuum cleaners or caught under furniture
- Wire insulation pierced by nails or screws
- Appliance cords affected by age, heat, or kinks
- Loose connections in outlets or switches
Where Are AFCIs Required?
Requirements vary by location, but generally, building codes specify that AFCIs must be installed in bedrooms and often other living areas. The 2006 International Residential Code (IRC) and the National Electrical Code (NEC) list places like family rooms, dining rooms, hallways, and more as AFCI-protected areas.
Kansas City AFCI requirements are adopted from the 2017 NFPA 70 (at the time of this writing.) It contains additional updates relevant to AFCI use, as well as some exceptions for certain areas. The 2017 language is presented here for reference.
NFPA 70 – 2017 on AFCI’s
210.12 Arc-Fault Circuit-Interrupter Protection
Arc-fault circuit-interrupter protection shall be provided as required in 210.12(A), (B), (C), and (D). The arc-fault circuit interrupter shall be installed in a readily accessible location.
(A) Dwelling Units
All 120-volt, single-phase, 15- and 20-ampere branch circuits supplying outlets or devices installed in dwelling unit kitchens, family rooms, dining rooms, living rooms, parlors, libraries, dens, bedrooms, sunrooms, recreation rooms, closets, hallways, laundry areas, or similar rooms or areas shall be protected by any of the means described in 210.12(A)(1) through (6):
- A listed combination-type arc-fault circuit interrupter, installed to provide protection of the entire branch circuit
- A listed branch/feeder-type AFCI installed at the origin of the branch-circuit in combination with a listed outlet branch-circuit type arc-fault circuit interrupter installed at the first outlet box on the branch circuit. The first outlet box in the branch circuit shall be marked to indicate that it is the first outlet of the circuit.
- A listed supplemental arc protection circuit breaker installed at the origin of the branch circuit in combination with a listed outletbranch-circuit type arc-fault circuit interrupter installed at the first outlet box on the branch circuit where all of the following conditions are met:
- The branch-circuit wiring shall be continuous from the branch-circuit overcurrent device to the outlet branch-circuit arc-fault circuit interrupter.
- The maximum length of the branch-circuit wiring from the branch-circuit overcurrent device to the first outlet shall not exceed 15.2 m (50 ft.) for a 14 AWG conductor or 21.3 m (70 ft.) for a 12 AWG conductor.
- The first outlet box in the branch circuit shall be marked to indicate that it is the first outlet of the circuit.
- A listed outletbranch-circuit type arc-fault circuit interrupter installed at the first outlet on the branch circuit in combination with a listed branch-circuit overcurrent protective device where all of the following conditions are met:
- The branch-circuit wiring shall be continuous from the branch-circuit overcurrent device to the outlet branch-circuit arc-fault circuit interrupter.
- The maximum length of the branch-circuit wiring from the branch-circuit overcurrent device to the first outlet shall not exceed 15.2 m (50 ft.) for a 14 AWG conductor or 21.3 m (70 ft.) for a 12 AWG conductor.
- The first outlet box in the branch circuit shall be marked to indicate that it is the first outlet of the circuit.
- The combination of the branch-circuit overcurrent device and outlet branch-circuit AFCI shall be identified as meeting the requirements for a system combination-type AFCI and shall be listed as such.
- If RMC, IMC, EMT, Type MC, or steel-armored Type AC cables meeting the requirements of 250.118, metal wireways, metal auxiliary gutters, and metal outlet and junction boxes are installed for the portion of the branch circuit between the branch-circuit overcurrent device and the first outlet, it shall be permitted to install a listed outlet branch-circuit type AFCI at the first outlet to provide protection for the remaining portion of the branch circuit.
- Where a listed metal or nonmetallic conduit or tubing or Type MC cable is encased in not less than 50 mm (2 in.) of concrete for the portion of the branch circuit between the branch-circuit overcurrent device and the first outlet, it shall be permitted to install a listed outlet branch-circuit type AFCI at the first outlet to provide protection for the remaining portion of the branch circuit.
Exception: Where an individual branch circuit to a fire alarm system installed in accordance with 760.41(B) or 760.121(B) is installed in RMC, IMC, EMT, or steel-sheathed cable, Type AC or Type MC, meeting the requirements of 250.118, with metal outlet and junction boxes, AFCI protection shall be permitted to be omitted.
Informational Note No. 1: For information on combination-type and branch/feeder-type arc-fault circuit interrupters, see UL 1699-2011, Standard for Arc-Fault Circuit Interrupters. For information on outlet branch-circuit type arc-fault circuit interupters, see UL Subject 1699A, Outline of Investigation for Outlet Branch Circuit Arc-Fault Circuit-Interrupters. For information on system combination AFCIs, see UL Subject 1699C, Outline of Investigation for System Combination Arc-Fault Circuit Interrupters.
Informational Note No. 2: See 29.6.3(5) of NFPA 72 -2013, National Fire Alarm and Signaling Code, for information related to secondary power-supply requirements for smoke alarms installed in dwelling units.
Informational Note No. 3: See 760.41(B) and 760.121(B) for power-supply requirements for fire alarm systems.
Note for Home Owners: Checking for compliance to building codes, either current or historic, is beyond the scope of a home inspection.
Types of AFCIs
AFCIs are available as circuit breakers that go into the home’s main electrical panel.
Nuisance Tripping
AFCIs sometimes trip even when no real danger is present, which can be inconvenient if it stalls power to a fridge or freezer. Electrical contractors can perform a few checks to reduce these “nuisance trips,” such as verifying wire connections and ensuring no shared neutral connections.
Arc Faults vs. Ground Faults
AFCIs and Ground Fault Circuit Interrupters (GFCIs) serve different purposes. While AFCIs prevent fires from arc faults, GFCIs are designed to protect people from electric shock by stopping the circuit if electricity leaks to a grounded object. Both offer safety but in different ways.
In Summary
AFCIs are essential for detecting and stopping electrical arcs that could lead to fires, protecting both homes and their occupants.
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