AFCI Breaker Symbol
Definition: The AFCI Breaker symbol represents an Arc-Fault Circuit Interrupter circuit breaker in residential and commercial wiring diagrams, denoting a protective device that detects the unique electrical signatures of dangerous arcing faults — both parallel (line-to-neutral) and series (line-to-line) arcs — and trips the circuit to prevent electrical fires, as required by ANSI/NFPA 70 (National Electrical Code) for bedroom, living area, and most habitable room circuits since NEC 2008, with Line and Load terminals.
Also known as: AFCI breaker, arc-fault circuit interrupter, arc-fault breaker, AFCI circuit breaker, combination AFCI, CAFCI, AFCI CB, arc-fault interrupter.
What the AFCI Breaker symbol means
The AFCI Breaker symbol in a wiring diagram or panel schedule identifies a circuit breaker with built-in arc-fault detection electronics. Unlike a standard circuit breaker that only responds to sustained overloads and short-circuits, the AFCI breaker continuously monitors the current waveform for the high-frequency signatures characteristic of electrical arcing caused by damaged insulation, loose connections, pinched wires, or deteriorated cords. When an arcing pattern is detected, the AFCI breaker trips within milliseconds to interrupt the circuit before the arc can ignite surrounding combustible materials.
In residential panel schedules, the AFCI Breaker symbol — often marked 'AF' or shown with a distinctive marking — designates circuits protecting bedrooms, kitchens, living rooms, hallways, and other habitable spaces as specified by the NEC. The Line terminal connects to the panel bus bar and the Load terminal feeds the protected branch circuit wiring.
How to identify the AFCI Breaker symbol
The AFCI Breaker symbol is drawn as the standard circuit breaker symbol (a rectangular block with Line and Load terminals and an internal toggle/mechanism indicator) with an additional 'AF', 'AFCI', or 'Arc Fault' label or annotation. Some schematic conventions use a modified breaker symbol with a wave or spark symbol inside the block to indicate the arc-detection function. In panel-layout wiring diagrams the AFCI breaker is typically distinguished from standard breakers by a distinctive face label noting 'Arc Fault Circuit Interrupter' required by UL 1699.
Function in a circuit
The AFCI breaker combines the standard overcurrent protection function (tripping on sustained overload or short-circuit current) with a digital signal processor that continuously monitors the circuit current for arc-fault signatures. Series arcs (occurring in the conductor itself due to a loose wire or deteriorated connection) and parallel arcs (between conductors) each produce characteristic high-frequency current patterns that the AFCI electronics identify and distinguish from normal loads such as motor start-up surges and dimmer harmonics. A combination AFCI (CAFCI) detects both series and parallel arcs and is the type required by the NEC. Detection, decision, and trip action occur within one to two AC half-cycles.
Standards: IEC vs ANSI
| IEC 60617 | IEC 62606 (General requirements for arc fault detection devices) is the international equivalent standard for AFDD (Arc Fault Detection Devices). IEC-region wiring diagrams may show the AFCI/AFDD symbol as a standard breaker symbol annotated with 'AFDD' per IEC 60617-7 circuit protection conventions. |
|---|---|
| ANSI/IEEE 315 | UL 1699 (Standard for Arc-Fault Circuit-Interrupters) is the primary product safety standard for AFCI breakers in North America. ANSI/NFPA 70 (National Electrical Code), Article 210.12, mandates AFCI protection for listed branch circuits. Schematic symbols follow ANSI Y32.2 / IEEE 315-1975 breaker symbol conventions with AFCI annotation. |
| Key difference | IEC regions use the term 'AFDD' (Arc Fault Detection Device) governed by IEC 62606, which may be a separate add-on device rather than an integrated breaker. North American practice uses 'AFCI' as an integrated circuit breaker per UL 1699 / NFPA 70. The schematic symbols are functionally similar: a breaker block with arc-detection annotation. |
Terminals / pins
| Pin | Name |
|---|---|
| line | Line |
| load | Load |
Typical values
Standard ratings: 15A and 20A (residential branch circuits), 120V AC. Interrupt capacity: 10,000A AIC standard. Trip time: 1–2 half-cycles upon arc detection. Series arc detection threshold: typically arcs ≥8A. Test button: present on all UL 1699-listed AFCI breakers. Pigtail neutral wire: included on AFCI breakers for neutral bus connection.
Where the AFCI Breaker symbol is used
- Bedroom branch circuits (NEC 2002 requirement, NEC 210.12)
- All 15A and 20A, 120V habitable room circuits in new construction per NEC 2014+ (kitchens, living rooms, hallways, closets)
- Dining room, family room, and sunroom circuits in residential remodels
- Dormitory rooms, hotel/motel guest rooms under NEC 2020 requirements
- Retrofit installations replacing standard breakers in older homes to improve arc-fault fire protection
- Circuits feeding in-wall wiring in finished basements and attics per NEC 2020
- Any branch circuit where wiring passes through walls, behind cabinets, or under floors where inspection after installation is impractical
Example
In the panel schedule of a new residential construction wiring diagram, a 15A AFCI Breaker symbol is shown feeding the bedroom circuit (branch 3), with the Line terminal connected to the 120V hot bus bar and the Load terminal connected to the 14 AWG/2-conductor branch circuit wiring; a pigtail white neutral wire connects from the AFCI breaker's neutral terminal to the neutral bus bar — the AFCI Breaker symbol tells the electrician that a listed AFCI breaker (not a standard breaker) must be installed to meet NEC 210.12 requirements.
Key facts
- The AFCI Breaker symbol represents a circuit breaker with built-in arc-fault detection that trips when it detects the high-frequency current signatures of dangerous electrical arcing, in addition to providing standard overload and short-circuit protection.
- Combination AFCI (CAFCI) breakers detect both series arcs (loose connections in the conductor) and parallel arcs (arcing between conductors), and are the type required by ANSI/NFPA 70 (NEC) Article 210.12.
- AFCI breakers are required by NEC 2008 and later in bedrooms, and by NEC 2014 and later in most 15A/20A, 120V habitable room circuits in new construction.
- AFCI breakers are tested and listed under UL 1699 in North America; the IEC equivalent standard is IEC 62606 for Arc Fault Detection Devices (AFDDs).
- The AFCI breaker includes a white pigtail wire that must connect to the neutral bus bar, distinguishing it physically from a standard breaker which only has line and load screw terminals.
- All UL 1699-listed AFCI breakers include a test button that simulates an arc fault to verify the detection circuit is operational.
- The AFCI Breaker symbol has two terminal pins: Line (connecting to the panel bus bar) and Load (connecting to the protected branch circuit).
Frequently asked questions
What does the AFCI breaker symbol mean on a wiring diagram?
The AFCI breaker symbol means an Arc-Fault Circuit Interrupter breaker is required at that panel position. This breaker detects the high-frequency signatures of electrical arcing caused by damaged wires, loose connections, or deteriorated insulation, and trips the circuit to prevent electrical fires — in addition to providing normal overload and short-circuit protection.
What does the AFCI breaker symbol look like?
The AFCI breaker symbol looks like a standard circuit breaker symbol (a rectangle with Line and Load terminals and a trip mechanism) with an additional 'AFCI', 'AF', or 'Arc Fault' annotation. In panel-layout diagrams it may be distinguished by a shaded or marked breaker face. The physical breaker has a prominent 'ARC FAULT CIRCUIT INTERRUPTER' label and a test button per UL 1699 requirements.
What is the difference between an AFCI breaker and a standard circuit breaker?
A standard circuit breaker only trips on sustained overcurrent (overload) or short-circuit. An AFCI breaker adds a digital signal processor that detects arcing-fault current signatures — high-frequency, intermittent current patterns — that a standard breaker ignores. Arcing faults cause the majority of residential electrical fires, which is why the NEC mandates AFCI protection for habitable room circuits.
Where is an AFCI breaker required by the NEC?
ANSI/NFPA 70 (NEC) Article 210.12 requires AFCI breakers on all 15A and 20A, 120V branch circuits supplying outlets and devices in dwelling unit bedrooms (NEC 2002+), and in kitchens, family rooms, dining rooms, living rooms, parlours, libraries, dens, sunrooms, recreation rooms, closets, hallways, laundry rooms, and similar areas in new construction (NEC 2014+).
What is the difference between an AFCI breaker and an AFCI/GFCI combo breaker?
An AFCI-only breaker provides arc-fault protection but not ground-fault protection for personnel (GFCI). An AFCI/GFCI combination breaker provides both arc-fault detection and ground-fault protection (5mA trip threshold), satisfying both NEC 210.12 (AFCI) and NEC 210.8 (GFCI) requirements simultaneously for circuits where both are mandated, such as kitchen and bathroom circuits in new construction.
What standard defines the AFCI breaker?
AFCI breakers in North America are listed under UL 1699 (Standard for Arc-Fault Circuit-Interrupters) and required by ANSI/NFPA 70 (NEC) Article 210.12. The IEC equivalent is IEC 62606 (General requirements for arc fault detection devices, AFDDs). Schematic symbols follow ANSI Y32.2 / IEEE 315-1975 circuit breaker symbol conventions with AFCI annotation.
How many terminals does the AFCI breaker symbol have?
The AFCI breaker symbol has two power terminals: Line (hot bus connection in the panel) and Load (branch circuit hot wire). Physical AFCI breakers also include a white pigtail wire that connects to the neutral bus bar, which is required for the arc-detection electronics to monitor the complete circuit current — standard breakers do not have this neutral pigtail.
Place the AFCI Breaker symbol on a wiring diagram or schematic in the free online circuit diagram maker — no download required.