TN LLE Electrical Safety Practices 2 — Questions and Answers
Question 1: Per OSHA 1910.333, what is the minimum approach distance for an unqualified person near exposed energized parts at 300 volts to ground?
- 3 feet
- 10 feet (Correct answer)
- 42 inches
- No specific distance, just 'stay away'
Correct answer: 10 feet
OSHA 1910.333(c)(3) Table S-5 specifies that unqualified persons must maintain at least 10 feet from exposed energized parts operating at 300V to 750V.
OSHA 1910.333(c)(3) Table S-5 provides approach distances for unqualified persons. For voltages from 301V to 750V, the minimum distance is 10 feet. For voltages up to 50V, no specific distance is required. Between 51V and 300V, the distance is 3.5 feet. These distances are significantly greater than qualified worker distances because unqualified persons lack the training and PPE to safely work near energized conductors.
Question 2: What is the primary purpose of an energized electrical work permit per NFPA 70E?
- To document insurance coverage
- To formally evaluate the hazard and justify why de-energizing is infeasible (Correct answer)
- To assign blame if an accident occurs
- To schedule the work with the utility company
Correct answer: To formally evaluate the hazard and justify why de-energizing is infeasible
An energized electrical work permit per NFPA 70E 130.2 documents the justification for not de-energizing and ensures proper safety measures are in place.
NFPA 70E Section 130.2 requires an energized electrical work permit when work will be performed on energized conductors or circuit parts that have not been placed in an electrically safe work condition. The permit must document: the description of work, justification for not de-energizing, shock and arc flash hazard analysis results, safe work practices to be employed, PPE requirements, and management approval. This formal process ensures that energized work is only performed when de-energizing creates a greater hazard or is infeasible.
Question 3: What does the term 'lockout/tagout' (LOTO) refer to in electrical safety?
- Locking the main entrance during electrical work
- Applying a physical lock and warning tag to energy-isolating devices to prevent re-energization (Correct answer)
- Tagging electrical panels for identification
- Locking tools in a secure location during breaks
Correct answer: Applying a physical lock and warning tag to energy-isolating devices to prevent re-energization
LOTO involves physically locking energy-isolating devices in the off position and attaching a warning tag to prevent accidental re-energization during maintenance.
Lockout/tagout (LOTO) per OSHA 1910.147 and NFPA 70E involves applying a lock and tag to each energy-isolating device (disconnect switch, circuit breaker, valve) to physically prevent re-energization while workers perform maintenance. Each worker applies their own lock, and the equipment cannot be re-energized until all locks are removed. Tags provide identification of who applied the lock and when. LOTO is the foundation of establishing an electrically safe work condition.
Question 4: Per NFPA 70E, what must be done to verify an electrically safe work condition after de-energizing equipment?
- Visual inspection only
- Test with a voltmeter to verify absence of voltage (Correct answer)
- Ask a coworker to confirm the circuit is off
- Check the breaker position only
Correct answer: Test with a voltmeter to verify absence of voltage
NFPA 70E requires testing each conductor with an adequately rated voltage detector to verify absence of voltage before establishing an electrically safe work condition.
NFPA 70E 120.5 requires that after de-energizing and applying LOTO, each conductor or circuit part must be tested with an adequately rated voltage detector to verify it is de-energized. Before and after testing, the voltage detector must be verified on a known voltage source to confirm it is functioning properly. This 'test-before-touch' protocol with a live-dead-live verification sequence ensures the voltage tester itself is working correctly and the circuit is truly de-energized.
Question 5: What class of fire extinguisher is required for electrical fires?
- Class A
- Class B
- Class C (Correct answer)
- Class D
Correct answer: Class C
Class C fire extinguishers are rated for fires involving energized electrical equipment. The extinguishing agent is non-conductive.
Class C fire extinguishers contain non-conductive extinguishing agents suitable for fires involving energized electrical equipment. Common Class C agents include CO2 and dry chemical. Many extinguishers carry multiple ratings such as ABC, meaning they can handle ordinary combustibles, flammable liquids, and electrical fires. Once the electrical equipment is de-energized, the fire becomes a Class A or B fire depending on the burning material. Tennessee LLEs should ensure appropriate fire extinguishers are available when performing electrical work.
Question 6: What is the minimum arc flash PPE category for work on a 480V motor control center with the doors open per NFPA 70E Table 130.7(C)(15)(a)?
- Category 1
- Category 2 (Correct answer)
- Category 3
- Category 4
Correct answer: Category 2
NFPA 70E Table 130.7(C)(15)(a) typically assigns PPE Category 2 for working on 480V MCCs with doors open under normal conditions.
NFPA 70E Table 130.7(C)(15)(a) provides arc flash PPE categories based on equipment type and task. For 480V motor control centers, working with doors open typically requires PPE Category 2, which includes arc-rated clothing with a minimum rating of 8 cal/cm2, arc-rated face shield or flash suit hood, safety glasses, hearing protection, and leather gloves. The specific category can vary based on the available fault current and clearing time — an incident energy analysis may indicate higher or lower requirements.
TN LLE Electrical Safety Practices 2
Per OSHA 1910.333, what is the minimum approach distance for an unqualified person near exposed energized parts at 300 volts to ground?