UNIT 1.1 — SAFETY

Jobsite safety and lockout/tagout (LOTO)

CERT 1 · DC/AC Theory & Safety · ~8 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.

Before any conductor is touched, the circuit must be de-energized and verified dead. Lockout/tagout (LOTO) is the procedure that guarantees a circuit cannot be re-energized while someone is working on it: the disconnecting means is opened, physically locked, and tagged with the worker's identity.

Verification is a three-step ritual: test your meter on a known live source, test the circuit you believe is dead, then re-test your meter on the known live source. This 'live-dead-live' check protects you from a failed meter giving a false zero.

Current, not voltage, is what injures the human body. As little as 50 mA across the chest can cause ventricular fibrillation. Voltage matters because it drives current through your body's resistance — which drops dramatically when skin is wet or broken.

Exam focus: safety questions are recall questions. Know the threshold currents, the verification sequence, and that a tag without a lock is never sufficient.

Perception threshold

≈ 1 mA

Let-go threshold

≈ 10 mA

Fibrillation risk

≈ 50 mA

Knowledge check

Quiz — 3 questions

1. What is the correct meter verification sequence before touching a circuit?

2. Which quantity is most directly responsible for injury to the body?

3. A LOTO tag without a lock is:

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