Licensed Electrical Contractor Troubleshooting & Maintenance 3

Question 1

A lighting circuit dims noticeably when a large appliance starts. What is the primary cause?

Accepted Answer

Excessive voltage drop due to undersized wiring or loose connections

Answer

Voltage drop caused by undersized conductors or high-resistance connections causes lights to dim when high-inrush loads start.

Question 2

When troubleshooting a tripped thermal-magnetic breaker, you find the breaker is warm but the circuit is lightly loaded. What should you suspect?

Accepted Answer

A loose connection at the breaker lug causing resistance heating

Answer

A warm breaker under light load suggests a loose lug connection creating resistance, which generates heat even at low current levels.

Question 3

A 120V outlet measures 105V under load and 118V at no load. This is best described as:

Accepted Answer

Excessive voltage drop indicating a wiring problem

Answer

A 13V drop under load far exceeds the NEC 5% recommendation (6V) and indicates a high-resistance fault in the wiring or connections.

Question 4

During PM on a motor control center (MCC), you find carbon tracking on the bus insulation. The correct action is to:

Accepted Answer

De-energize, clean with appropriate solvent, and inspect for the arc source

Answer

Carbon tracking provides a conductive path for future arcing; the bus must be de-energized, cleaned, and the root cause corrected.

Question 5

A circuit breaker fails to trip during an overload test. The most appropriate action is to:

Accepted Answer

Replace the breaker immediately — a breaker that won't trip is a fire hazard

Answer

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.

Licensed Electrical Contractor Practice Test