ESC Electrical Equipment Maintenance & Inspection 3 — Questions and Answers
Question 1: According to NFPA 70E, what is required before an electrician opens an energized electrical panel cover for inspection?
- A verbal authorization from a supervisor
- An energized electrical work permit and appropriate PPE based on the arc flash hazard analysis (Correct answer)
- A standard work order and safety glasses
- Written approval from the facility manager only
Correct answer: An energized electrical work permit and appropriate PPE based on the arc flash hazard analysis
NFPA 70E requires an energized electrical work permit and PPE selected based on incident energy analysis or PPE category before opening energized panels.
Question 2: A power transformer's oil sample shows a high concentration of acetylene (C₂H₂) during dissolved gas analysis (DGA). What fault condition does this most likely indicate?
- Thermal degradation of cellulose insulation below 150°C
- High-energy electrical arcing inside the transformer (Correct answer)
- Partial discharge at low energy levels
- Normal aging of the mineral oil
Correct answer: High-energy electrical arcing inside the transformer
Acetylene is produced only by high-energy electrical arcing and is a critical fault gas indicating an active arc discharge inside the transformer.
Question 3: Which maintenance task is most critical for ensuring proper operation of a thermal-magnetic circuit breaker's overload protection function?
- Cleaning the arc chutes with compressed air
- Exercising the breaker by manually tripping and resetting it
- Verifying calibration of the thermal element via injection testing (Correct answer)
- Inspecting and tightening the line and load lugs
Correct answer: Verifying calibration of the thermal element via injection testing
Injection testing verifies that the bimetallic thermal element trips within the required time-current curve parameters, confirming overload protection accuracy.
Question 4: When performing contact resistance testing on switchgear bus connections, which instrument is used and what does an abnormally high reading indicate?
- Megohmmeter; indicates insulation leakage current
- Low-resistance ohmmeter (DLRO); indicates a loose or corroded connection (Correct answer)
- Clamp-on ammeter; indicates current imbalance
- Phase rotation meter; indicates reversed phase sequence
Correct answer: Low-resistance ohmmeter (DLRO); indicates a loose or corroded connection
A DLRO (Ducter) measures micro-ohm contact resistance, and high values indicate loose bolting or corrosion that will cause heating under load current.
Question 5: What is the primary purpose of exercising (operating) a disconnect switch or circuit breaker during scheduled electrical maintenance?
- To reset the electronic trip unit memory
- To prevent oxidation buildup and verify mechanical operation (Correct answer)
- To test the ground fault protection system
- To measure load current with the breaker in a test position
Correct answer: To prevent oxidation buildup and verify mechanical operation
Exercising switching devices removes oxide buildup on contacts and confirms that the mechanical operating mechanism functions correctly when needed.
Question 6: Under NFPA 70B 2023, which practice is specifically recommended for maintaining motor branch circuit protective devices?
- Replacing fuses with circuit breakers of equivalent rating for simplicity
- Verifying that fuse clips provide firm contact and that fuse ratings match the motor's nameplate (Correct answer)
- Uprating fuses by one size to prevent nuisance blowing during motor starts
- Using any available fuse type as long as the ampere rating is correct
Correct answer: Verifying that fuse clips provide firm contact and that fuse ratings match the motor's nameplate
NFPA 70B recommends confirming fuse clip tension and correct fuse ratings to ensure reliable overcurrent protection matched to the motor nameplate.
Question 7: A maintenance technician finds that the arc flash label on a panelboard lists an incident energy of 8 cal/cm². Which PPE category is the minimum required for energized work on this equipment?
- PPE Category 1 (4 cal/cm² minimum arc rating)
- PPE Category 2 (8 cal/cm² minimum arc rating) (Correct answer)
- PPE Category 3 (25 cal/cm² minimum arc rating)
- PPE Category 4 (40 cal/cm² minimum arc rating)
Correct answer: PPE Category 2 (8 cal/cm² minimum arc rating)
PPE Category 2 has a minimum arc rating of 8 cal/cm², which meets the requirement for equipment with an incident energy of 8 cal/cm².
ESC Electrical Equipment Maintenance & Inspection 3
According to NFPA 70E, what is required before an electrician opens an energized electrical panel cover for inspection?