Electrical Contractor Troubleshooting & Maintenance Flashcards
6 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 6 Electrical Contractor Troubleshooting & Maintenance flashcards as text
A three-phase motor is drawing unbalanced current across phases but voltage at the motor terminals is balanced. What is the most likely cause?
Answer: Damaged motor winding
Balanced voltage with unbalanced current draw indicates a winding fault within the motor itself, such as shorted turns on one phase.
After replacing a VFD, the motor runs but produces excessive noise and vibration. What should the contractor check first?
Answer: VFD carrier frequency setting
A VFD carrier frequency set too low produces audible noise and vibration in the motor; adjusting it to 4-8 kHz typically resolves the issue.
When performing preventive maintenance on a 1,200A switchboard, what must be done before retorquing bus bar connections?
Answer: Perform a lockout/tagout and verify zero energy
LOTO and zero-energy verification is mandatory before any direct contact with bus bar connections to prevent arc flash and electrocution.
A ground fault indicator on a 480V ungrounded delta system is showing a ground on Phase B. What is the correct troubleshooting approach?
Answer: Isolate circuits one at a time while monitoring the indicator
Systematically isolating circuits while monitoring the ground fault indicator identifies which branch circuit contains the fault without unnecessary shutdowns.
What tool is most appropriate for locating an open conductor inside a finished wall without damaging the surface?
Answer: Tone generator and probe
A tone generator and inductive probe can trace and locate the break point in a conductor hidden behind finished walls without any demolition.
During a scheduled maintenance shutdown, a contractor discovers pitting on the contacts of a 200A contactor. What is the correct action?
Answer: Replace the contactor entirely
Pitted contactor contacts have reduced cross-sectional area and compromised surface integrity, requiring full replacement rather than resurfacing.