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 240V circuit is reading 120V at the outlet. What is the most likely cause?
Answer: Open neutral on the circuit
An open neutral on a 240V circuit causes each leg to read only 120V to ground instead of the full 240V across both legs.
When troubleshooting a motor that hums but does not start, which component should be checked first?
Answer: Start capacitor
A humming but non-starting motor typically indicates a failed start capacitor that cannot provide the phase shift needed to generate starting torque.
What does a megohmmeter reading of 0.5 MΩ on a 480V motor winding indicate?
Answer: Failed insulation requiring immediate attention
The minimum acceptable insulation resistance for a 480V motor is 1 MΩ plus 1 MΩ per kV, so 0.5 MΩ indicates dangerously degraded insulation.
During thermal imaging of a panelboard, one breaker shows significantly higher temperature than adjacent breakers carrying similar loads. What is the most probable cause?
Answer: Loose connection at the breaker terminal
A loose connection creates high-resistance contact points that generate excess heat, which thermal imaging easily detects.
A commercial building experiences intermittent voltage sags. The utility feed tests normal. Where should the contractor investigate next?
Answer: Main distribution panel connections
Intermittent voltage sags with a normal utility feed most commonly originate from loose or corroded connections at the main distribution panel.
What is the recommended maintenance interval for retorquing electrical connections in commercial switchgear per NFPA 70B?
Answer: Annually
NFPA 70B recommends annual retorquing of bolted electrical connections in commercial switchgear to prevent loose connections and thermal failures.