STSC Electrical Safety in Construction 4 — Questions and Answers
Question 1: Under OSHA 29 CFR 1926.404, what is the maximum allowable ground fault current before a GFCI must trip?
- 2 milliamps
- 5 milliamps (Correct answer)
- 10 milliamps
- 15 milliamps
Correct answer: 5 milliamps
GFCIs are designed to trip at 4–6 milliamps, with 5 milliamps being the standard threshold cited by OSHA for construction site protection.
Question 2: Which condition makes an assured equipment grounding conductor program (AEGCP) an acceptable alternative to GFCIs on a construction site?
- When the worksite has no standing water
- When equipment is rated for outdoor use
- When a written program with required inspections and records is maintained (Correct answer)
- When temporary wiring is 10 AWG or larger
Correct answer: When a written program with required inspections and records is maintained
OSHA allows an AEGCP as a GFCI alternative only when the employer maintains a written program that includes required visual inspections and records of testing.
Question 3: A supervisor notices extension cords are being routed through doorways where doors pinch the cord. What is the primary hazard?
- Voltage drop causing equipment malfunction
- Insulation damage that can cause shock or fire (Correct answer)
- Overloading the circuit breaker
- Cord becoming a trip hazard
Correct answer: Insulation damage that can cause shock or fire
Pinching or crushing extension cord insulation can expose conductors, creating shock and fire hazards from arcing or direct contact.
Question 4: What is the minimum safe approach distance for unqualified workers near unguarded energized parts operating at 50 kV?
- 5 feet
- 10 feet (Correct answer)
- 15 feet
- 20 feet
Correct answer: 10 feet
OSHA 1926.416 requires unqualified workers to stay at least 10 feet away from unguarded energized lines or parts up to 50 kV.
Question 5: When must a construction supervisor verify overhead power line voltages before allowing equipment to operate nearby?
- Only when equipment will pass directly under lines
- Whenever equipment will operate within 20 feet of overhead lines
- Always, before any work begins on site (Correct answer)
- Only when lines are not insulated
Correct answer: Always, before any work begins on site
OSHA requires determining line voltage before work begins so the correct safe approach distance can be established and maintained.
Question 6: Which type of fire extinguisher must be used on an energized electrical fire?
- Class A (water-based)
- Class B (CO2 or dry chemical)
- Class C (CO2, dry chemical, or halon) (Correct answer)
- Class D (dry powder)
Correct answer: Class C (CO2, dry chemical, or halon)
Class C extinguishers use non-conductive agents such as CO2, dry chemical, or halon, which are safe for energized electrical equipment.
Question 7: A 120-volt temporary lighting string has a broken lamp socket exposing bare wires. What is the correct immediate action?
- Wrap the exposed wires with electrical tape and continue work
- Replace the string before returning it to service (Correct answer)
- Reduce circuit load to limit current through the defect
- Post a warning sign and monitor the condition
Correct answer: Replace the string before returning it to service
Damaged temporary lighting must be removed from service and replaced; tape repairs do not restore the original insulation integrity required by OSHA.
STSC Electrical Safety in Construction 4
Under OSHA 29 CFR 1926.404, what is the maximum allowable ground fault current before a GFCI must trip?