Question 61
A 480 V to 208/120 V three-phase transformer is feeding a panelboard. The calculated load on the 208/120 V side is 75 kVA. Approximately what full-load current flows on the 208 V line side?
Question 62
During testing of a feeder, you measure 120 V from phase A to neutral, 120 V from phase B to neutral, and 0 V from phase A to phase B. What is the most likely explanation?
Question 63
Which statement about three-phase, 4-wire wye systems is generally correct?
Question 64
A three-phase, four-wire wye system feeds a panel with many nonlinear loads such as computer power supplies. What can occur on the neutral conductor?
Question 65
A single-phase, 120 V load draws 8 A. What is the real power consumed by the load if it is purely resistive?
Question 66
In a three-phase panel supplying a mix of single-phase 120 V loads in a commercial building, what is the primary goal when assigning circuits to phases?
Question 67
A three-phase, 480 V motor draws 30 A at a power factor of 0.8. Approximately how much real power in kilowatts is the motor using?
Question 68
You have a 3-phase, 4-wire, 120/208 V system. What is the approximate line-to-line voltage between two phase conductors?
Question 69
A 3-phase, 4-wire wye system feeds an unbalanced panelboard load with different currents on each phase but no major harmonics. How does the neutral current compare?
Question 70
In a three-phase system, what is the relationship between line current and phase current in a balanced delta-connected load?
Question 71
A three-phase motor nameplate shows 9 leads for low-voltage connection. What type of connection is most commonly used for low-voltage operation in US motor diagrams?
Question 72
A 480/277 V, 3-phase, 4-wire wye system supplies a fluorescent lighting panel. What is the typical voltage between a phase conductor and neutral?
Question 73
A 3-phase, 4-wire panelboard serves both 3-phase and single-phase loads. How are single-phase 208 V loads typically connected?
Question 74
You are installing a 4-wire, 3-phase receptacle for a piece of equipment requiring an equipment grounding conductor. Which conductors must be included?
Question 75
A 30 kVA, 208Y/120 V three-phase panelboard is fully loaded at its rated capacity. Approximately what line current will flow in each phase conductor at full load?
Question 76
You are asked to balance loads in a three-phase panelboard. Which approach best helps achieve this?
Question 77
On a three-wire, single-phase 120/240 V dwelling service, what is the nominal voltage between the two ungrounded (hot) conductors?
Question 78
On a three-phase, 4-wire wye system, what is the typical voltage from any phase conductor to the neutral in a 120/208 V system?
Question 79
A three-phase panelboard is fed from a 120/208 V system. A journeyperson wants to balance the panel's single-phase loads. What is the primary goal when assigning circuits?
Question 80
In a star (Wye) connected three-phase system, how is the line voltage related to the phase voltage?
Question 81
In the US, which color is generally used to identify the ungrounded (hot) conductor in a $277/480 \text{ V}$ three-phase system, when using the high leg color for a $120/208 \text{ V}$ system (Delta with center tap)?
Question 82
A $480/277 \text{ V}$ 3-phase, 4-wire Wye service is being installed. Which of the following is considered an **ungrounded** (hot) conductor in this system?
Question 83
In a $480\text{ V}$ 3-phase, 3-wire Delta system, what is the voltage measured between any two phase conductors (line-to-line)?
Question 84
A 3-phase panelboard supplies a mix of lighting and receptacle loads. To help balance phase loading, how should the circuits generally be arranged?
Question 85
A 3-phase, 4-wire wye system supplies both 3-phase motor loads and 120 V receptacle loads. An electrician notices that one phase conductor is significantly hotter than the others under normal operation. Which is the MOST likely cause?
Question 86
A 480/277 V, three-phase panelboard feeds multiple fluorescent lighting circuits at 277 V. When one phase loses power, what happens to the lighting loads on that phase?
Question 87
A 120/240 V single-phase panel has the following existing loads: Phase A total 40 A, Phase B total 20 A. You plan to add a new 20 A, 120 V circuit. To best balance the panel, which phase should you place the new circuit on?
Question 88
A fluorescent lighting circuit uses electronic ballasts rated for 120-277 V. The building supply is 277/480 V three-phase, and the ballast is connected line-to-neutral on the 277 V system. What is the approximate phase-to-phase voltage of this system?
Question 89
A 120/208 V, 3-phase, 4-wire panelboard supplies a 3-phase balanced motor load drawing 30 A per phase at 208 V. What is the total three-phase power delivered to the motor?
Question 90
A 3-phase, 4-wire wye system has a phase voltage of 277V. What is the line-to-line voltage?