What an AFCI senses
An arc changes the shape of the current, not how much flows. You crush a cord or drive a nail into a cable and watch an AFCI breaker count the arcs while a plain breaker holds.
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What to try
- 1Start on Heater. The current is a smooth wave, so the AFCI has nothing to count.
- 2Pick Crushed cord and drag the bed onto the cord. The wave goes ragged and the AFCI counts the arcs.
- 3Set Breaker type to Plain breaker and crush the cord again. The arc keeps charring the cord, and the plain breaker holds.
NEC 2026 sections it covers
- 210.12(B)
- New bedroom circuits in a home need AFCI protection.
- 210.12(A)(1)
- A combination AFCI breaker is one way to provide it.
- 210.12(E)
- Older homes need it when a bedroom circuit is changed.
- 210.23(B)(1)
- A 1500 W heater is more than 80% of a 15 A circuit, so it gets 20 A.
- 300.6(A)(1)
- A bored hole stays 1-1/4 in. from the stud face, or the cable gets a steel plate.
- 314.29
- Splices go in boxes you can get to.
- 406.26
- Receptacles in a home are tamper-resistant.
Section numbers only. Read the full text in your code book. Temperatures and times in the visual are teaching models.
See something wrong? Tell us and we will check it against the code.
Practice it and teach it
- Protection Map simulationProtect a whole house with GFCI and AFCI devices on a budget, and pass the inspector.
- GFCI and AFCI lessonGFCI and AFCI protection (NEC 2026 210.8, 210.12)
More visuals
- Breaker and wirePlug in loads and watch the wire heat up when the breaker is too big for it.
- What a GFCI sensesCurrent goes out and comes back. See what happens when a little goes missing through a person.
- What trips a breakerOn an overload, a strip that bends with heat trips the breaker slowly. On a short or a ground fault, a magnet trips it at once.