STSC Electrical Safety in Construction 2 — Questions and Answers
Question 1: What is the voltage range classified as 'high voltage' under NFPA 70E for arc flash hazard analysis purposes?
- Above 120V
- Above 240V
- Above 600V (Correct answer)
- Above 1,000V
Correct answer: Above 600V
NFPA 70E and OSHA classify voltages above 600V as 'high voltage,' triggering more stringent arc flash and electrical safety requirements including greater approach boundaries and higher-rated arc flash PPE.
Under NFPA 70E and OSHA's electrical standards, 600V is the dividing line between standard and high-voltage requirements. Equipment rated over 600V requires: engineering controls such as remote racking, energized work permits, increased approach boundaries (flash protection, limited, and restricted), higher arc flash PPE ratings (cal/cm²), and a qualified electrical engineer involved in arc flash hazard analysis. Construction sites frequently encounter 480V (below threshold) for most temporary power, but medium-voltage systems (4,160V–15,000V) for large crane power and temporary utility feeds fall into high-voltage category.
Question 2: Under OSHA 1926.416, what does the term 'qualified person' mean in the context of electrical work on a construction site?
- Any worker who has completed a 10-hour OSHA construction safety course
- A person who has received training in and has demonstrated skills and knowledge related to the construction and operation of electrical equipment (Correct answer)
- A licensed master electrician only
- Any worker assigned to electrical tasks by their supervisor
Correct answer: A person who has received training in and has demonstrated skills and knowledge related to the construction and operation of electrical equipment
A qualified person (electrical) under OSHA 1926.416 is one who has demonstrated skills and knowledge related to electrical equipment operation and construction, and has received safety training on the hazards involved.
Per OSHA 1926.416(a)(1) and definitions in 1926.32, a 'qualified person' for electrical work is one who has received training in and has demonstrated skills and knowledge relative to the construction and operation of electrical equipment and installations and has received safety training to recognize and avoid electrical hazards. This definition is broader than requiring a licensed electrician — a journeyman electrician, industrial electrician, or other trained trades person may qualify. However, certain tasks (utility-level work, work on live parts above 600V) may require specific licenses depending on state regulations.
Question 3: A power tool's power cord on a construction site shows evidence of insulation damage (cracked, frayed sheath). What is the CORRECT action?
- Wrap the damaged area with electrical tape and continue use
- Remove from service, tag out, and arrange for proper repair or replacement (Correct answer)
- Reduce the tool's load to compensate for the damaged insulation
- Report the damage at end of shift and continue working carefully
Correct answer: Remove from service, tag out, and arrange for proper repair or replacement
Damaged insulation on a power cord is a shock and electrocution hazard. The tool must be immediately removed from service, tagged out to prevent use, and repaired or replaced by qualified personnel.
OSHA 1926.416(e)(1) prohibits the use of electrical equipment with frayed, defective, or deteriorated insulation. Electrical tape repairs on damaged cords are not an acceptable substitute for proper repair because tape cannot reliably restore the original dielectric properties and may mask worsening damage. The correct procedure is: stop using the tool, attach a 'Do Not Use' tag, and remove it from service for repair by a qualified person or replacement. Pre-use visual inspection of cords is part of the Assured Equipment Grounding Conductor Program requirement.
Question 4: Which of the following correctly describes the 'limited approach boundary' in electrical safety?
- The distance at which a flash burn could cause permanent injury
- The closest distance an unqualified person may approach energized conductors without special authorization (Correct answer)
- The distance within which arc flash can ignite worker clothing
- The perimeter of the electrical exclusion zone marked by warning tape
Correct answer: The closest distance an unqualified person may approach energized conductors without special authorization
The Limited Approach Boundary (NFPA 70E) is the distance from an exposed energized conductor within which unqualified persons may not enter unless escorted and protected. Beyond this boundary, workers need limited training; within it, full electrical safety precautions apply.
NFPA 70E establishes three approach boundaries for electrical work: (1) Flash Protection Boundary — the distance at which an unprotected person could receive a second-degree burn from an arc flash; (2) Limited Approach Boundary — unqualified persons may not cross without being escorted by a qualified person and wearing appropriate PPE; (3) Restricted Approach Boundary — only qualified persons wearing full arc flash PPE may enter. The Arc Flash Boundary is calculated based on available fault current and clearing time — it may extend further than the limited approach boundary on high-energy systems.
Question 5: What type of fire extinguisher is required for electrical fires on a construction site?
- Class A (water-based)
- Class B (CO2 or dry chemical)
- Class C (CO2, dry chemical, or clean agent) (Correct answer)
- Class D (dry powder for metal fires)
Correct answer: Class C (CO2, dry chemical, or clean agent)
Class C fire extinguishers are required for electrical fires. Class C designation indicates the extinguishing agent is non-conductive, preventing shock to the person using the extinguisher.
Class C fire extinguishers use non-conductive extinguishing agents — typically CO2, dry chemical (monoammonium phosphate or sodium bicarbonate), or halon-replacement clean agents. The C classification indicates the agent will not conduct electricity back to the user during discharge. Class A (water) and Class B (foam) agents are conductive and can cause electrocution when used on energized electrical equipment. Many construction sites use ABC multi-purpose dry chemical extinguishers, which are rated for Class A, B, and C fires. When the power source can be de-energized, the fire reclassifies as Class A and water-based extinguishers become appropriate.
Question 6: What minimum PPE must workers wear when working on or near exposed energized electrical parts on a construction site according to OSHA 1926.416?
- Safety glasses and leather gloves
- Insulated gloves rated for the voltage, safety glasses, and non-conductive footwear (Correct answer)
- Only insulated tools are required — PPE is optional
- Full arc flash suit at all times near any energized equipment
Correct answer: Insulated gloves rated for the voltage, safety glasses, and non-conductive footwear
OSHA 1926.416 and NFPA 70E require insulated gloves rated for the working voltage, safety glasses or face protection, and non-conductive footwear as minimum PPE for work near exposed energized parts.
Per OSHA 1926.416(a)(2)(i), workers exposed to electrical hazards must use insulating mats, insulating boots, insulated gloves, and other protective equipment appropriate to the voltage and task. At minimum, insulated rubber gloves (rated for the voltage class), safety glasses with side shields, and non-conductive footwear are required for work near energized parts. For tasks with arc flash exposure potential, NFPA 70E Table 130.5(G) specifies the required arc-rated PPE based on the incident energy at the work location. A full arc flash suit is required only when incident energy levels calculated from the hazard analysis require it.
STSC Electrical Safety in Construction 2
What is the voltage range classified as 'high voltage' under NFPA 70E for arc flash hazard analysis purposes?