After a circuit is de-energized by a circuit protective device, the circuit may not be manually re-energized until it has been determined that the equipment and circuit can be safely energized.
The repetitive manual reclosing of circuit breakers or re-energizing circuits through replaced fuses is prohibited.
Source: 29 CFR 1910.334(b)(2), OSHA General Industry Electrical Standards
Definition (Article 100): A state in which an electrical conductor or circuit part has been disconnected from energized parts, locked/tagged in accordance with established standards, tested for the absence of voltage, and if necessary, temporarily grounded for personnel protection.
Article 120.6 — Process for Establishing and Verifying an ESWC: The 2024 edition clarifies that absence-of-voltage testing must occur at each point of work. The 8-step process includes: identify all sources → open disconnecting devices → verify visually → apply LOTO → release stored energy → test for absence of voltage (live-dead-live) → ground if necessary.
Live-Dead-Live (Step 7): Use an adequately rated portable test instrument to test each conductor or circuit part at each point of work, both phase-to-phase and phase-to-ground. Before and after each test, verify the instrument operates correctly on a known voltage source.
Source: NFPA 70E-2024, Articles 100 & 120.6
This trainer operates at 24 VDC — below the 50 V threshold referenced in OSHA 1910.333(a)(1). Electric shock risk is negligible under normal conditions.
However: The troubleshooting PROCEDURES taught here — LOTO, absence-of-voltage verification, systematic diagnosis before reclosing — apply identically to 480 V, 4160 V, or any voltage. Teach the right habits at safe voltages so they're automatic when the stakes are real.
Even 24 VDC can produce arc flash at high fault currents (battery banks, large DC bus systems) and can ignite flammable atmospheres.