UNIT 2.2 — PROTECTION

Breakers, GFCI, and AFCI protection

CERT 2 · Residential Wiring · ~10 min

Community content — not verified by a licensed electrician. Lessons and questions here are written for study practice and pinned to NEC 2023. Code editions and local amendments vary by jurisdiction. Always confirm against your adopted code book and your licensing board's published exam outline before test day.

A standard circuit breaker protects *wiring* from overload (sustained over-current, thermal trip) and short circuit (massive instantaneous current, magnetic trip). It does not protect people: a breaker rated 15 A is perfectly content to pass 50 mA through your chest indefinitely.

GFCI (ground-fault circuit interrupter) protection protects *people*: it compares current leaving on the hot with current returning on the neutral, and trips in milliseconds at a 4–6 mA imbalance — current escaping through an unintended path, possibly you. Required where water lives: bathrooms, kitchens, garages, outdoors, basements.

AFCI (arc-fault circuit interrupter) protection protects against *fires*: it recognizes the electronic signature of arcing from damaged cords or loose connections and opens the circuit. Required in most dwelling living areas.

Exam focus: match the device to what it protects (breaker→wire, GFCI→people, AFCI→fire), the 4–6 mA GFCI threshold, and location requirements.

Breaker

Protects wiring

GFCI

People · trips 4–6 mA

AFCI

Fire · arc signatures

Knowledge check

Quiz — 3 questions

1. A GFCI trips when it detects:

2. A standard thermal-magnetic breaker primarily protects:

3. AFCI protection is designed to prevent:

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