ASP Electrical Safety 5 — Questions and Answers
Question 1: What is 'step potential' and why is it hazardous near a downed power line?
- The voltage required to step up current in a transformer
- The voltage difference between two points on the ground surface that can drive current through a person's legs and body (Correct answer)
- The minimum voltage to energize a step-down transformer
- The rated stepping load on an electrical platform
Correct answer: The voltage difference between two points on the ground surface that can drive current through a person's legs and body
Step potential is the voltage gradient across the ground near a fault or downed conductor; a person standing with feet at different distances from the source completes a circuit through their legs.
Question 2: What does the term 'flash protection boundary' mean in NFPA 70E arc flash analysis?
- The distance beyond which arc flash PPE is no longer required because incident energy is below 1.2 cal/cm² (Correct answer)
- The boundary of the electrical room where flash photography is prohibited
- The radius around a panel within which only licensed electricians may work
- The distance at which an arc flash will cause automatic circuit breaker tripping
Correct answer: The distance beyond which arc flash PPE is no longer required because incident energy is below 1.2 cal/cm²
The flash protection boundary is the distance at which incident energy equals 1.2 cal/cm², the threshold for a second-degree burn, and marks where arc flash PPE is required.
Question 3: Which class of fire extinguisher is appropriate for energized electrical equipment fires?
- Class A
- Class B
- Class C (Correct answer)
- Class D
Correct answer: Class C
Class C extinguishers use non-conductive agents (such as CO₂ or dry chemical) suitable for fires involving energized electrical equipment.
Question 4: An arc flash hazard analysis identifies an incident energy level of 25 cal/cm² at the worker's position. What arc flash PPE category (per NFPA 70E) is required at minimum?
- Category 1 (4 cal/cm² min rating)
- Category 2 (8 cal/cm² min rating)
- Category 3 (25 cal/cm² min rating) (Correct answer)
- Category 4 (40 cal/cm² min rating)
Correct answer: Category 3 (25 cal/cm² min rating)
NFPA 70E PPE Category 3 covers incident energies up to 25 cal/cm²; the worker's PPE must be rated at or above the calculated incident energy.
Question 5: What distinguishes a 'qualified person' from an 'unqualified person' under OSHA electrical standards?
- A qualified person holds a licensed electrician's certificate issued by the state
- A qualified person has been trained and demonstrated skills and knowledge related to electrical equipment construction and hazards (Correct answer)
- A qualified person has more than five years of electrical work experience
- A qualified person wears all required PPE when working near electrical equipment
Correct answer: A qualified person has been trained and demonstrated skills and knowledge related to electrical equipment construction and hazards
OSHA defines a qualified person as one who has received training in and demonstrated skills and knowledge of electrical equipment, including hazard recognition and safe work practices.
Question 6: Which condition makes a portable electrical tool most likely to create a ground fault shock hazard for the user?
- Using the tool in an area with low ambient humidity
- A damaged or missing equipment grounding conductor in the supply cord (Correct answer)
- Operating the tool at a voltage rating lower than the supply voltage
- Using a heavy-duty extension cord with the tool
Correct answer: A damaged or missing equipment grounding conductor in the supply cord
A missing or broken equipment grounding conductor means fault current has no low-impedance return path, so it can flow through the user's body if the tool casing becomes energized.
Question 7: What is the purpose of applying an insulating cover or guard on nearby energized conductors when working in close proximity?
- To reduce the conductor's operating temperature
- To prevent accidental contact with energized parts that are within the limited or restricted approach boundary (Correct answer)
- To improve the conductor's current-carrying capacity
- To protect conductors from physical damage by falling tools
Correct answer: To prevent accidental contact with energized parts that are within the limited or restricted approach boundary
Insulating covers or rubber blankets guard exposed energized conductors near the work area to prevent inadvertent contact when a worker cannot maintain required approach distances.
ASP Electrical Safety 5
What is 'step potential' and why is it hazardous near a downed power line?