Licensed Electrical Contractor Electrical Contractor Troubleshooting & Maintenance 3

Question 1

A three-phase motor is drawing unbalanced current across phases but voltage at the motor terminals is balanced. What is the most likely cause?

Accepted Answer

Damaged motor winding

Answer

Utility supply issue

Answer

Oversized motor starter

Answer

Incorrect overload relay setting

Question 2

After replacing a VFD, the motor runs but produces excessive noise and vibration. What should the contractor check first?

Accepted Answer

VFD carrier frequency setting

Answer

Motor bearings

Answer

Supply voltage to the VFD

Answer

Motor alignment

Question 3

When performing preventive maintenance on a 1,200A switchboard, what must be done before retorquing bus bar connections?

Accepted Answer

Perform a lockout/tagout and verify zero energy

Answer

Notify the utility company

Answer

Wear voltage-rated gloves only

Answer

Take thermal images first

Question 4

A ground fault indicator on a 480V ungrounded delta system is showing a ground on Phase B. What is the correct troubleshooting approach?

Accepted Answer

Isolate circuits one at a time while monitoring the indicator

Answer

Immediately de-energize the entire system

Answer

Replace the Phase B fuse

Answer

Check only Phase B branch circuits

Question 5

What tool is most appropriate for locating an open conductor inside a finished wall without damaging the surface?

Accepted Answer

Tone generator and probe

Answer

Multimeter

Answer

Time-domain reflectometer

Answer

Thermal imaging camera

Question 6

During a scheduled maintenance shutdown, a contractor discovers pitting on the contacts of a 200A contactor. What is the correct action?

Accepted Answer

Replace the contactor entirely

Answer

File the contacts smooth and reinstall

Answer

Clean contacts with electrical cleaner and reuse

Answer

Apply dielectric grease and monitor