Use the openings the box was made for, protect the conductors going through them, and close the ones you are not using.
An open knockout is a hole in the enclosure. The enclosure exists to contain what happens inside it, and a hole is the enclosure not doing its job.
A knockout you removed and did not use is not a small thing left over. The box was designed as a closed enclosure with openings where they belong, and an extra hole changes what it is. The parts to close one cost almost nothing and take seconds, which is exactly why the step gets skipped.
Check yourself: An unused knockout is on the back of the box, against the wall where nobody will ever see it. Does it need closing?
Answer: Yes. An unused hole is not finished simply because it is out of sight.
The requirement is about the enclosure being closed, not about whether the hole is visible. Out of sight changes who notices it, not what it does.
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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