ESC Electrical Equipment Maintenance & Inspection 2 — Questions and Answers
Question 1: During a visual inspection of a motor control center (MCC), you notice discoloration and charring around one circuit breaker. What is the most appropriate immediate action?
- Log the observation and schedule repair for the next maintenance window
- De-energize and lock out the affected circuit before further investigation (Correct answer)
- Apply insulating spray to prevent arcing and continue operations
- Increase the breaker's trip setting to reduce nuisance tripping
Correct answer: De-energize and lock out the affected circuit before further investigation
Charring and discoloration indicate a potential arc flash or overheating condition requiring immediate de-energization and LOTO before any further work.
Question 2: What is the recommended minimum frequency for infrared thermography (IR) scanning of critical electrical equipment under NFPA 70B guidelines?
- Every 5 years
- Annually (Correct answer)
- Every 6 months
- Monthly
Correct answer: Annually
NFPA 70B recommends infrared thermography at least annually for critical electrical equipment to detect hot spots before failures occur.
Question 3: A technician performing maintenance on a distribution transformer measures insulation resistance. Which test method applies a stepped voltage to evaluate insulation condition over time?
- Polarization Index (PI) test
- Dielectric absorption ratio (DAR) test
- Step voltage test (Correct answer)
- Hipot (high-potential) test
Correct answer: Step voltage test
The step voltage test applies progressively increasing voltages to identify insulation weaknesses that would not be detected at a single test voltage.
Question 4: When inspecting flexible cords used with portable electrical equipment, which defect requires immediate removal from service?
- Minor surface abrasion on the outer jacket with no exposed conductors
- A cord longer than 25 feet used for temporary power
- Exposed or damaged inner conductor insulation (Correct answer)
- A cord rated for 15A used on a 15A circuit
Correct answer: Exposed or damaged inner conductor insulation
Exposed or damaged inner conductor insulation creates a direct shock and fire hazard, requiring the cord to be immediately removed from service.
Question 5: What does a Polarization Index (PI) value below 1.0 indicate about electrical insulation?
- The insulation is in excellent condition
- The insulation has absorbed moisture or is contaminated and likely defective (Correct answer)
- The test voltage was too low to provide meaningful data
- The equipment is operating within normal parameters
Correct answer: The insulation has absorbed moisture or is contaminated and likely defective
A PI value below 1.0 indicates severely deteriorated, wet, or contaminated insulation that poses an imminent failure risk.
Question 6: Which OSHA standard requires employers to establish and implement written procedures for the control of hazardous energy during electrical equipment servicing and maintenance?
- 29 CFR 1910.303
- 29 CFR 1910.147 (Correct answer)
- 29 CFR 1910.269
- 29 CFR 1910.132
Correct answer: 29 CFR 1910.147
29 CFR 1910.147 (the Control of Hazardous Energy standard) requires written LOTO procedures for equipment servicing and maintenance.
Question 7: During switchgear inspection, what condition in a draw-out circuit breaker's racking mechanism indicates it should be taken out of service?
- Slight resistance when racking to the test position
- Damaged or missing secondary disconnect fingers (Correct answer)
- A thin film of approved contact lubricant on the primary contacts
- A breaker frame that rattles slightly when the door is closed
Correct answer: Damaged or missing secondary disconnect fingers
Damaged or missing secondary disconnect fingers prevent control power and protective relay signals from reaching the breaker, rendering protection systems inoperable.
ESC Electrical Equipment Maintenance & Inspection 2
During a visual inspection of a motor control center (MCC), you notice discoloration and charring around one circuit breaker.
What is the most appropriate immediate action?