Licensed Electrical Contractor Electrical Contractor Troubleshooting & Maintenance 1

Question 1

A GFCI outlet on a 20A circuit trips immediately when reset. You measure 0Ω between the neutral and ground conductors at the outlet. What is the most likely cause?

Accepted Answer

A neutral-to-ground fault downstream of the GFCI device

Answer

Overloaded circuit requiring a larger breaker

Answer

Defective GFCI outlet that needs replacement

Answer

Reversed line and load terminals on the GFCI outlet

Question 2

A three-phase 480V motor runs normally under no-load but trips the overload relay within minutes when connected to its load. Voltage at the motor terminals measures 478V on all three phases. What is the most likely cause?

Accepted Answer

Overload relay sized too low for the actual full-load amperage of the motor

Answer

Voltage imbalance causing excess heat in the windings

Answer

Open phase on the supply side of the motor starter

Answer

Failing capacitor causing low power factor

Question 3

You are troubleshooting a 120V lighting circuit where the lights flicker intermittently. Voltage at the fixture measures between 108V and 122V during the flicker. What should you investigate first?

Accepted Answer

Check for a loose or corroded connection in the circuit, including at the panel

Answer

Replace the fixtures with higher-wattage lamps

Answer

Install a voltage regulator at the main service entrance

Answer

Upgrade the circuit to 20A from 15A

Question 4

After replacing a single-phase 240V water heater element, the new element fails within two weeks. The voltage across the element measures 240V and resistance of the element tests good. What is the most probable cause of repeated element failure?

Accepted Answer

Sediment buildup causing the element to overheat due to low water level in the tank

Answer

Incorrect wattage element installed for the tank rating

Answer

Improper wire gauge feeding the water heater circuit

Answer

Voltage sag during high-demand periods damaging the element

Question 5

An insulation resistance test on a 277V fluorescent lighting circuit reads 1.2 MΩ. After running the HVAC system for 30 minutes, the reading drops to 0.18 MΩ. What does this indicate?

Accepted Answer

Moisture intrusion in the conduit or junction boxes that worsens when HVAC airflow increases

Answer

The test equipment is malfunctioning due to electrical interference from the HVAC

Answer

Normal insulation degradation from age that requires full circuit replacement

Answer

A wiring error causing a neutral-to-ground fault on the lighting panel

Question 6

A 200A residential service panel shows visible arcing marks on the neutral bus bar at one terminal. The conductor at that terminal is a 10 AWG wire from a 20A branch circuit. What is the correct repair procedure?

Accepted Answer

Identify and correct the loose connection, clean the bus bar, and torque the terminal to specification

Answer

Replace only the neutral bus bar and retighten all conductors to manufacturer torque specs

Answer

Clean the arcing marks, apply anti-oxidant compound, and retighten the terminal

Answer

Replace the entire service panel because arcing on the neutral bus indicates a failed bus bar