CHST Electrical Safety and LOTO 2 — Questions and Answers
Question 1: Under OSHA 1926.416, what minimum clearance must be maintained from overhead energized power lines rated at 50 kV or below when using equipment on a construction site?
- 10 feet (Correct answer)
- 6 feet
- 15 feet
- 20 feet
Correct answer: 10 feet
OSHA 1926.416(a)(1) and OSHA 1926.600 require a minimum clearance of 10 feet from any part of a tool, equipment, or machinery to overhead power lines rated at 50 kV or less.
Overhead power line contact is a leading cause of construction fatalities. OSHA 1926.416(a)(1) establishes a minimum 10-foot clearance from energized overhead lines rated 50 kV or below. For lines rated above 50 kV, clearance increases by 4 inches for every 10 kV above 50 kV. Before starting work near overhead lines, employers must contact the utility to determine voltage and either de-energize lines or install insulating guards.
Question 2: What is the primary purpose of Lockout/Tagout (LOTO) procedures under OSHA 29 CFR 1910.147?
- To control hazardous energy and prevent the unexpected energization or release of stored energy during servicing and maintenance (Correct answer)
- To document equipment maintenance history
- To alert workers of equipment that is out of service for repairs
- To establish a chain of custody for equipment keys
Correct answer: To control hazardous energy and prevent the unexpected energization or release of stored energy during servicing and maintenance
OSHA 1910.147 establishes LOTO as the procedure for controlling hazardous energy — electrical, mechanical, hydraulic, pneumatic, chemical, thermal — to protect workers during equipment servicing and maintenance.
The Control of Hazardous Energy standard (29 CFR 1910.147) requires employers to establish a program to prevent the unexpected energization, startup, or release of stored energy. This includes all forms of energy: electrical, mechanical, hydraulic, pneumatic, gravitational, chemical, and thermal. The employer must develop written energy control procedures, provide employee training, and perform periodic inspections. Lockout devices are preferred over tagout-only when equipment can be locked out.
Question 3: Ground Fault Circuit Interrupters (GFCIs) are required by OSHA on construction sites. How quickly does a GFCI interrupt a circuit when a fault is detected?
- Within 1/40th of a second (approximately 25 milliseconds) (Correct answer)
- Within 1 second
- Within 5 seconds
- Within 100 milliseconds
Correct answer: Within 1/40th of a second (approximately 25 milliseconds)
GFCIs are designed to trip within 1/40th of a second (approximately 25 milliseconds) when they detect a ground fault of 5 milliamps or more, fast enough to prevent electrocution.
A GFCI monitors the difference in current between the hot and neutral conductors. When a ground fault of 4 to 6 milliamps is detected, it opens the circuit within 1/40th of a second (25 ms). This is fast enough to prevent lethal electrocution. OSHA 1926.404(b)(1) requires GFCIs or an Assured Equipment Grounding Conductor Program on all construction site 120V receptacles.
Question 4: Under OSHA 1926.404, an Assured Equipment Grounding Conductor Program (AEGCP) is an alternative to GFCIs. How often must cord sets and equipment be visually inspected under an AEGCP?
- Before each day's use (Correct answer)
- Weekly
- Monthly
- Each shift change
Correct answer: Before each day's use
Under an AEGCP, cord sets, receptacles not part of a building's wiring, and equipment connected by cord and plug must be visually inspected for external defects before each day's use.
OSHA 1926.404(b)(1)(iii) requires that under an Assured Equipment Grounding Conductor Program, all cord sets, receptacles not part of the permanent building wiring, and cord- and plug-connected equipment be visually inspected for damage before each day's use. Any damaged or defective equipment must be removed from service. Additionally, the equipment must be tested for continuity and correct attachment of grounding conductors at intervals not exceeding 3 months.
Question 5: What PPE is required when working on energized electrical systems with exposed live parts above 50 volts?
- Rubber insulating gloves rated for the voltage level, worn with leather protectors (Correct answer)
- Standard leather work gloves and safety glasses
- Insulated boots only
- Dielectric hard hat and safety glasses only
Correct answer: Rubber insulating gloves rated for the voltage level, worn with leather protectors
NFPA 70E and OSHA require rubber insulating gloves rated for the voltage level being worked on, worn with leather protectors to prevent mechanical damage, when working on energized electrical parts.
Rubber insulating gloves (RIGs) are the primary personal protective equipment for electrical work involving exposed live parts above 50 volts. They must be tested and rated to the class appropriate for the maximum voltage present. Leather protectors are worn over the rubber gloves to protect against punctures and cuts. Additional PPE such as arc flash face shields and flame-resistant clothing may also be required depending on the incident energy level.
Question 6: Which electrical hazard involves a sudden release of energy from an unintended arc path that can produce temperatures up to 35,000°F and cause severe burns?
- Arc flash (Correct answer)
- Ground fault
- Overload
- Transient overvoltage
Correct answer: Arc flash
Arc flash is a sudden release of energy caused by an electrical arc, producing intense heat, pressure waves, and molten metal that can cause severe burns even at low voltages.
An arc flash occurs when current flows through an unintended arc path between conductors or between a conductor and ground. Even at voltages below 600V, arc flash events can release enormous energy — potentially thousands of calories per square centimeter — causing severe or fatal burns, blindness, hearing damage, and blast injuries. NFPA 70E requires arc flash hazard analysis to determine arc flash boundaries and appropriate PPE including arc-rated clothing and face shields.
CHST Electrical Safety and LOTO 2
Under OSHA 1926.416, what minimum clearance must be maintained from overhead energized power lines rated at 50 kV or below when using equipment on a construction site?
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