What is AFCI protection and where is it required?

AFCI — arc-fault circuit interrupter — protection is a device that detects the unique electrical signature of a dangerous arc (from damaged, loose, or deteriorated wiring) and shuts the circuit off before it can start a fire. Where GFCI prevents shock, AFCI prevents fire, and California requires it across most of an ADU's habitable 120V circuits. Coverage is shown on the panel schedule.

Where AFCI protection is required

AFCI protection is generally required on 120-volt, 15- and 20-amp branch circuits supplying outlets and devices in:

• Bedrooms and all sleeping rooms.
• Living rooms, family rooms, and dens.
• Hallways, closets, and similar habitable spaces.
• Kitchens and laundry areas (where the adopted code cycle requires it).

In practice, recent code editions have expanded AFCI to nearly all 120V circuits serving habitable rooms, so on a modern ADU panel the majority of branch breakers carry AFCI protection.

How it's provided

• AFCI circuit breaker — the most common method; protects the entire branch circuit from the panel.
• Combination AFCI/GFCI (dual-function) breaker — used where a circuit needs both kinds of protection, such as a kitchen or laundry circuit, so one device satisfies both requirements.
• AFCI receptacle — occasionally used in retrofit or extension scenarios where a breaker swap isn't practical.

Why it matters on ADUs and conversions

AFCI is a relatively recent requirement, so older unpermitted units and garage conversions frequently predate it entirely — making missing AFCI protection one of the most common corrections in ADU legalization cases.

Because AFCI and GFCI address different hazards — fire versus shock — many habitable circuits require both, which is why dual-function breakers appear throughout a typical ADU panel schedule. On our electrical plans, every circuit's AFCI and GFCI designation is called out on the panel schedule so the plan reviewer and your electrician both see exactly which breaker type each circuit needs. Requirements vary by jurisdiction and code cycle — confirm the exact AFCI scope with your local building department. See the ADU electrical guide for how AFCI, GFCI, and the code circuits fit together.