Troubleshooting & Maintenance Techniques Flashcards
7 cards from real CME practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Troubleshooting & Maintenance Techniques flashcards as text
A technician uses a two-lead voltage tester and measures 120V between a neutral conductor and ground at a receptacle. What does this reading indicate?
Answer: A high-resistance or open connection exists in the neutral conductor
Voltage between neutral and ground at a receptacle indicates current is flowing through the equipment grounding conductor due to a high-resistance or open neutral connection, creating a voltage difference.
When troubleshooting an intermittent circuit fault that only occurs under load, which maintenance technique is MOST effective for identifying the problem location?
Answer: Infrared thermography scan while circuit is energized under load
Infrared thermography identifies high-resistance connections by their heat signature while the circuit is operating under load — the exact conditions that cause intermittent failures.
A power factor correction capacitor bank installation causes nuisance tripping of upstream breakers at energization. What is the MOST likely cause?
Answer: High inrush current during capacitor energization exceeds instantaneous trip setting
Capacitor banks draw a high inrush current spike at the moment of energization; if the upstream breakers have a low instantaneous trip setting, this momentary spike trips the breaker even though steady-state current is within rating.
During maintenance of a 480V switchgear lineup, what is the recommended safe practice before racking out a circuit breaker?
Answer: Verify zero energy by opening the breaker, locking it out, and testing for absence of voltage
NFPA 70E lockout/tagout requires opening the breaker, applying lockout/tagout, and verifying absence of voltage with a rated test instrument before any contact with potentially energized parts.
A submersible pump motor fails repeatedly with burned windings. Megohmmeter testing of the motor winding passes each time before reinstallation. What additional diagnostic step is MOST important?
Answer: Test the control panel overload relay heater sizing against the motor FLA
Repeated winding failure despite passing insulation tests strongly suggests the overload protection heater elements are oversized and not protecting the motor from sustained overcurrent conditions.
A lighting contactor controlled by a time clock fails to open at the scheduled off time but opens correctly when manually tripped. What component is MOST likely faulty?
Answer: The time clock output contact is welded closed or stuck
If the contactor opens correctly on manual trip but not on the time clock schedule, the control signal from the time clock is not de-energizing the coil — a welded or stuck time clock output contact maintains the coil circuit.
When measuring insulation resistance on a newly installed cable system, what procedure must be followed to obtain a valid reading?
Answer: Discharge the cable capacitance fully before and after each test
Cable capacitance stores charge during megohmmeter testing; failure to fully discharge before and after testing can damage test equipment, give false readings, or create a shock hazard for personnel.