AFCI Requirement & Breaker Sizing Calculator
Pick a dwelling room to see whether NEC 2020 210.12 requires arc-fault protection, then get the standard 240.6(A) breaker and the minimum conductor for the load. The ampere rating of an AFCI breaker is identical to any other breaker; what this tool settles is which rooms are on the 210.12(A) list (and which are not, even though they are GFCI locations), and how the 210.12(D) extension rule applies.
How to use this calculator
- Select the dwelling room. The tool returns whether AFCI protection is required under NEC 210.12(A), or tells you the room is not on the list.
- Choose whether this is a new branch circuit or an extension/modification of an existing one, so the tool applies the 210.12(D) rule and its 6 ft exception.
- Set the circuit type (120 V 1-pole or 120/240 V multiwire 2-pole) and enter the load in amperes (or watts), split into continuous (3+ hours) and noncontinuous portions.
- Set conductor material and conditions to get the minimum conductor. Read the notes for device type, the 15/20 A amperage scope, and the AFCI-versus-GFCI overlap.
NEC reference
The AFCI requirement is set by NEC 2020 210.12. Dwelling units fall under 210.12(A), which lists the rooms and applies to 120-volt, single-phase, 15- and 20-ampere branch circuits supplying outlets or devices. Extensions and modifications of existing circuits are governed by 210.12(D). The breaker ampere rating follows the same rules as any breaker: NEC 210.20(A) (100% noncontinuous plus 125% continuous), rounded up to a 240.6(A) standard rating, with the conductor checked against the 240.4(D) small-conductor limits and 240.4(B) next-size-up flagged when used.
Results are for reference only. Verify against the applicable adopted edition of the NEC and consult a licensed electrician for code compliance.
NEC 2020 210.12(A) dwelling AFCI rooms
All 120-volt, single-phase, 15- and 20-ampere branch circuits supplying outlets or devices installed in these dwelling-unit rooms must be arc-fault protected:
| AFCI required (210.12(A)) | Not on the AFCI list |
|---|---|
| Kitchens | Bathrooms (GFCI, not AFCI) |
| Family rooms | Garages (GFCI, not AFCI) |
| Dining rooms | Outdoors (GFCI, not AFCI) |
| Living rooms | Unfinished basements |
| Parlors | Crawl spaces (GFCI, not AFCI) |
| Libraries | Attics (unfinished) |
| Dens | |
| Bedrooms | |
| Sunrooms | |
| Recreation rooms | |
| Closets | |
| Hallways | |
| Laundry areas | |
| Similar rooms or areas |
The 210.12(A) list is not numbered in the code, so every listed room cites the same 210.12(A). A finished, habitable basement or recreation room counts as a "similar room or area" and is required; an unfinished basement or attic is not. Dormitory units (210.12(B)) and guest rooms and guest suites (210.12(C)) carry their own lists that this tool does not evaluate.
AFCI versus GFCI: different jobs, different rooms
An AFCI detects the high-frequency signature of a dangerous arcing fault in the branch-circuit wiring and opens the circuit before the arc can start a fire. A GFCI measures the imbalance between the ungrounded and grounded conductors and trips on a small ground-fault current, 4 to 6 mA for a UL 943 Class A device, to protect people from shock. They solve different problems and their required-location lists only partly overlap.
Kitchens and laundry areas appear on both the 210.12 AFCI list and the 210.8 GFCI list, so those circuits need both kinds of protection, which a listed dual-function (AFCI/GFCI) device provides. Bathrooms, garages, outdoors, and crawl spaces are GFCI locations but not AFCI locations, so they need ground-fault protection without an arc-fault requirement. The tool flags the overlap for the room you choose.
Sizing an AFCI breaker: same ampere math
An AFCI circuit breaker is an ordinary thermal-magnetic breaker with an arc-fault sensor added, so its ampere rating is chosen exactly like any breaker. Apply NEC 210.20(A): the device must be rated at least 100% of the noncontinuous load plus 125% of the continuous load, then round up to a standard rating from 240.6(A). The conductor is sized to the same requirement and checked against the 240.4(D) small-conductor caps (copper 14/12/10 AWG at 15/20/30 A) so the breaker can legally protect it.
Because 210.12(A) applies to 15- and 20-ampere branch circuits, dwelling AFCI breakers are stocked as 15 A and 20 A devices, in both 1-pole (120 V) and 2-pole (120/240 V multiwire) versions. On a multiwire branch circuit the shared neutral must pass through the AFCI device so the sensor reads every circuit conductor. If a load sizes to a breaker larger than 20 A, the circuit is outside the 15/20 A range 210.12 governs, and the tool says so.
Frequently asked questions
Do bedrooms need AFCI protection?
Yes. Bedrooms are on the NEC 210.12(A) list, and have been the anchor AFCI location since arc-fault protection first entered the code. All 120-volt, 15- and 20-ampere branch circuits supplying outlets or devices in a dwelling bedroom must be AFCI protected.
Do bathrooms or garages need AFCI?
No. Bathrooms, garages, outdoors, unfinished basements, and crawl spaces are not on the 210.12(A) list. Several of them require GFCI protection under 210.8 instead, which is why the two are so often confused. Use the tool to see the AFCI-versus-GFCI status for a specific room.
Does extending a circuit trigger AFCI?
Usually. NEC 210.12(D) requires AFCI protection when an existing circuit in a covered area is modified, replaced, or extended, using a combination AFCI at the origin or an outlet-branch-circuit AFCI at the first receptacle. The exception is an extension of 6 ft or less that adds no new outlets or devices.
Why doesn't this work for motors and AC units?
Motor branch circuits (Article 430) and HVAC equipment (Article 440) size protection differently, and 210.12 arc-fault protection applies to 120 V 15/20 A outlet and device circuits, not those loads. Feed motor and HVAC circuits through the Motor Breaker Sizing Calculator or the nameplate instead.
Related calculators
- GFCI Breaker Sizing Calculator: the NEC 210.8 ground-fault requirement and GFCI breaker sizing, the companion to this tool.
- Breaker Size Calculator: general-use breaker and conductor sizing without the AFCI location check.
- Wire Size Calculator: full conductor sizing with voltage drop and OCPD together.
- Wire Ampacity Calculator: derated ampacity of a specific conductor.
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