Troubleshooting & Maintenance Flashcards
7 cards from real Licensed Electrical Contractor 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 flashcards as text
A lighting circuit dims noticeably when a large appliance starts. What is the primary cause?
Answer: Excessive voltage drop due to undersized wiring or loose connections
Voltage drop caused by undersized conductors or high-resistance connections causes lights to dim when high-inrush loads start.
When troubleshooting a tripped thermal-magnetic breaker, you find the breaker is warm but the circuit is lightly loaded. What should you suspect?
Answer: A loose connection at the breaker lug causing resistance heating
A warm breaker under light load suggests a loose lug connection creating resistance, which generates heat even at low current levels.
A 120V outlet measures 105V under load and 118V at no load. This is best described as:
Answer: Excessive voltage drop indicating a wiring problem
A 13V drop under load far exceeds the NEC 5% recommendation (6V) and indicates a high-resistance fault in the wiring or connections.
During PM on a motor control center (MCC), you find carbon tracking on the bus insulation. The correct action is to:
Answer: De-energize, clean with appropriate solvent, and inspect for the arc source
Carbon tracking provides a conductive path for future arcing; the bus must be de-energized, cleaned, and the root cause corrected.
A circuit breaker fails to trip during an overload test. The most appropriate action is to:
Answer: Replace the breaker immediately — a breaker that won't trip is a fire hazard
A breaker that fails to trip during a confirmed overload test is defective and must be replaced as it can no longer protect the circuit.
What does a 'hot-cold' pattern on a thermal imaging scan of a switchboard indicate?
Answer: A potential loose connection or overloaded conductor at the hot spot
A localized hot spot on thermal imaging relative to surrounding areas indicates increased resistance from a loose connection or overloaded conductor.
A 3-phase panel shows a neutral conductor that is significantly hotter than the phase conductors. What is the most likely cause?
Answer: High harmonic content from non-linear loads overloading the neutral
Non-linear loads (computers, VFDs, LED drivers) generate third-harmonic currents that add on the neutral rather than cancel, causing overheating.