A GFCI watches current going out and current coming back. If they stop matching, some of it is leaving by a path it should not be on.
Every amp that goes out is supposed to come back. When it does not, it is returning some other way -- and the most expensive version of "some other way" is through a person.
Both conductors pass through the same sensing ring, and their magnetic effects oppose. In a healthy circuit they cancel and the device sees nothing. Let some current leak away to earth instead of returning on the neutral, and the two no longer match -- the difference is what the GFCI is built to see. That is the clamp-meter principle from lesson 77 used as protection instead of measurement.
Check yourself: A circuit has GFCI protection. Does it still need its equipment grounding conductor and the safe work practices?
Answer: Yes. GFCI protection does not replace required grounding or safe work practices.
A GFCI reduces the consequence of current leaving the intended path. The equipment grounding conductor is what gives fault current a path back to its source so the protection operates at all, and safe work practice is what establishes a safe condition before you touch anything. Three different jobs, and no one of them covers the other two.
No card. No account needed to start. Score by topic against the 70% mark.
Written from the owner's poster for this lesson. Nothing added beyond what the poster states.
Written for Texas apprentices as free study material. The Texas apprentice licence is an application, not an exam (Occupations Code 1305.161), and nothing here counts as apprenticeship hours or continuing-education credit. VoltMark is not affiliated with, endorsed by, or sponsored by NFPA, PSI, TDLR, or any state or local licensing authority. Always follow your employer's safety programme and your supervising electrician.
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