Question 1
A motor nameplate shows 230 V, 1-phase, 60 Hz. What does this voltage value represent?
Question 2
On a schematic diagram, how are control circuit conductors typically shown compared to power circuit conductors?
Question 3
What is the primary purpose of a thermal overload relay in a motor starter?
Question 4
A 600V, 3-phase motor circuit has a blown fuse on L1. What voltage will be measured across the open fuse holder with the disconnect closed and motor trying to run?
Question 5
A 600V motor has a blown fuse on Phase A. You measure voltage across the open fuse holder while the motor is single-phasing. What voltage do you expect to see?
Question 6
A 10 HP motor trips its overload immediately upon pressing start. What is the most likely cause?
Question 7
Which test identifies a shorted turn in a motor winding?
Question 8
A motor is vibrating excessively. What is a likely mechanical cause?
Question 9
An electrician is troubleshooting a 3-phase motor that is running hot and making a humming sound. A current measurement shows 12A on Phase A, 12A on Phase B, and 0A on Phase C. What is the most likely cause?
Question 10
A 3-phase motor is running exceptionally hot and the current on one phase is significantly higher than the other two. After checking the supply voltages and finding them balanced, which internal fault is most likely?
Question 11
An electrician is troubleshooting a 3-phase motor that is running hot and humming. Measurement shows: Phase A = 12A, Phase B = 12A, Phase C = 0A. What is the most likely cause?
Question 12
An electrician finds that a 3-phase motor is running hot and drawing unequal currents on the three phases. After checking the supply, they find the voltages are balanced. Which internal fault is most likely?
Question 13
A 3-phase, Delta-connected motor is found to have one open stator winding. What symptom would likely be observed during operation under load?
Question 14
An electrician is troubleshooting a 3-phase motor that hums but will not start. Measurement shows Phase A = 12A, Phase B = 12A, and Phase C = 0A. What is the most likely cause?
Question 15
What is the main purpose of a control relay in a motor control circuit?
Question 16
A complex lighting control system in an office uses multiple relays and occupancy sensors. Some lights remain on after hours even when areas are unoccupied. What is the best systematic approach to troubleshoot this issue?
Question 17
You are troubleshooting a lighting circuit controlled by a single-pole switch. The lamps stay on even when the switch is in the 'off' position. Which wiring error is most likely?
Question 18
A dwelling bedroom circuit uses combination AFCI breakers. What is the primary reason for using AFCI protection in this location?
Question 19
During troubleshooting, you find that a motor contactor coil is not pulling in, even though the control circuit voltage is present at its terminals. What is the most likely next test?
Question 20
When troubleshooting a motor that hums but does not start, which of the following is the most likely cause?
Question 21
A motor overloads only when fully loaded mechanically. Current readings show Phase A: 20A, Phase B: 20A, Phase C: 20A. Nameplate FLA is 18A. What is the cause?
Question 22
A 3-phase motor has a nameplate rating of 10A. You measure 10A on Phase A, 10A on Phase B, but 0A on Phase C. The motor is humming and not turning. What is the problem?