AFCI

GFCI stops electrocution from ground faults by sensing hot/neutral imbalance.

AFCI stops fires from arc faults — plasma that can exceed 6000°C (~10,832°F).

Both may live in the panel as special breakers, but the hazard and sensing method differ. A circuit can need both protections where code requires.

Parallel arcs occur when conductors fault together — damaged lamp cord insulation letting hot and neutral touch, for example.

Current may be limited by conductor resistance, not load, but peaks can exceed normal breaker ratings. A solid short trips the magnetic element quickly; an intermittent short may heat the thermal element slowly — or persist on small conductors long enough to start fire.

Parallel arcs often eject hot metal into combustibles and are detected quickly because peak currents stand out to AFCI electronics.

Series arcs come from loose connections — loose receptacle screw, bad wire nut — so the load is in series with the arc gap.

Average current may stay below thermal/magnetic trip: example in the text — 12 A hair dryer on a loose terminal connects half the time → 6 A average, still below a 15 A breaker, but a 6 A arc locally is incandescent.

Standard thermomagnetic breakers cannot protect this scenario reliably. AFCIs watch for intermittent current signatures.

Not all arcing is a fault. Normal events include:

• toggling a light switch,
• motor relay pickup/dropout,
• plugging in an appliance that is already on,
• changing a bulb with power on,
• commutator/brushes on vacuum cleaners and drills.

The AFCI microprocessor compares magnitude, duration, and time between pulses to patterns in nonvolatile memory — not one fixed waveform. Some motor loads can nuisance-trip AFCIs because their waveforms resemble faults.

AFCI devices include current and temperature sensors so they still act as normal breakers on overload and short circuit. A manual test switch checks arc and short functions; the microprocessor also self-tests about every 10 minutes.

Failed self-test or test button means replace the device — not “leave it because the lights work.”

Connect like a GFCI breaker: pigtail neutral to panel neutral bar; branch neutral under silver screw, hot under brass screw — both through the breaker so the electronics can monitor the branch.

Dwelling-code requirements expanded over editions to many 120 V, 15–20 A branch circuits in living areas — verify local adoption for exact rooms and exceptions.

Tamper-resistant (TR) receptacles use internal shutters that open only when equal pressure is applied to both slots — blocking single-object insertion by children. Required in many dwelling locations such as playrooms, nurseries, and daycare areas alongside other receptacle rules.

TR is not AFCI — it prevents foreign objects in slots; AFCI still addresses arcing on the branch.

Vacuum cleaners, drills with brushes, and some motor loads produce waveforms the microprocessor may confuse with arcing. Before removing protection, try another circuit, a different appliance, or manufacturer troubleshooting steps. Series arc at a loose screw is exactly what you must not hide by swapping to a plain breaker.

Many dwelling panels now stack AFCI, GFCI, and standard thermal/magnetic duties in combination breakers. Read the handle label — not every two-pole device is an AFCI. Wire neutral through the breaker when instructions require it so both shock and fire sensing work.

After installation, run the TEST sequence and confirm normal loads run without tripping before you close the cover.

Series arcs love old back-stab receptacles, damaged lamp cords, and loose breaker lugs. AFCI is not a substitute for replacing failed devices — it is an early trip when arcing starts. During troubleshooting, feel for warmth, look for discoloration, and reterminate before resetting repeatedly.

Situation. A bedroom circuit keeps working but occupants smell hot plastic at a receptacle. Breaker never trips. Investigation finds a loose back-stab making intermittent contact — classic series arc. Average current stayed under breaker trip.

How to think with this lesson.

• This is why AFCI exists — series arcing below trip current.
• Tight terminations and listed methods beat “it still runs.”
• Where AFCI is required, an ordinary breaker leaves the fire path open.

Learning conclusion: loose connections can arc without tripping a standard breaker; AFCI adds fire-level arc detection.