Question 31
On an electrical single-line diagram, what does a symbol showing a transformer with a delta on the primary and a wye on the secondary indicate?
Question 32
In a three-phase, four-wire 120/208 V system feeding a balanced three-phase load, what is the approximate current in the neutral conductor?
Question 33
You measure 600 V between phases on a three-phase system, but only 200 V from each phase to ground. What condition might this indicate?
Question 34
A three-phase, four-wire panelboard is supplying line-to-neutral loads. How are the phase conductors typically identified?
Question 35
How many line conductors does a typical three-phase, 600 V, three-wire system have?
Question 36
You measure 120 V across a load and 4 A flowing through it. What is the resistance of the load?
Question 37
A 3-phase, 600 V, 10 A balanced load is supplied by a feeder. Approximately what is the total three-phase power if the power factor is 1?
Question 38
In a three-wire 120/240 V single-phase residential service, what is the voltage between the two ungrounded (hot) conductors?
Question 39
A 3-phase, 4-wire 120/208 V panelboard feeds a balanced 3-phase, 12 kVA lighting load. What is the line current on each phase?
Question 40
In a three-phase, four-wire wye system, what is the relationship between line voltage and phase voltage?
Question 41
A three-phase, 208 V, 10 kW load has a power factor of 0.8. Approximately what line current is drawn?
Question 42
In a three-phase, four-wire 120/208 V system, what is the approximate line-to-neutral voltage?
Question 43
Which of the following best describes three-phase power?
Question 44
In a 3-phase, 4-wire wye system, what is the usual relationship between line voltage and phase voltage?
Question 45
In a three-phase system, how many electrical degrees separate each of the phase voltages?
Question 46
A three-phase, 208 V, 10 hp motor has a full-load current of approximately 30 A. What is the approximate three-phase power in kilowatts if it operates at full load and near unity power factor?
Question 47
A 120/240 V single-phase, 3-wire service supplies a dwelling. Which conductors are present from the transformer secondary to the service equipment?
Question 48
On a three-phase panel schedule, each three-pole breaker is shown feeding a motor load. Why should motor loads be evenly distributed across phases when possible?
Question 49
In a three-phase, 4-wire wye system, what is the typical line-to-neutral voltage when the line-to-line voltage is 480 V?
Question 50
A 3-phase, 480 V, 10 hp induction motor can be connected in either delta or wye configuration. Compared with wye, what is a typical effect of a delta connection at the same line voltage?
Question 51
In a 120/240 V single-phase residential service, how many ungrounded (hot) conductors are typically supplied from the utility transformer to the main panel?
Question 52
In a 120/208 V three-phase panel serving lighting and receptacle loads, why is it important to balance the single-phase loads across all three phases?
Question 53
A three-phase, 208 V panel supplies a balanced 30 kVA load. Approximately what line current does the panel carry?
Question 54
In a three-phase, four-wire wye system, what is the typical line-to-neutral voltage when the line-to-line voltage is 480 V?
Question 55
Which statement best describes a three-phase system compared to a single-phase system of the same line voltage?
Question 56
In a standard North American three-phase, four-wire wye system, what is the typical line-to-line voltage if the line-to-neutral voltage is 120 V?
Question 57
A three-phase, 4-wire panelboard supplies both three-phase and single-phase loads. What is the function of the neutral bus in this panel?
Question 58
In a three-phase system, which connection type provides two different line-to-line voltages from one transformer secondary?
Question 59
A 480 V, three-phase motor draws 30 A at full load. Approximately what is its kVA load?
Question 60
In a three-phase, four-wire wye system supplying balanced linear loads, what is the current in the neutral conductor compared to the phase conductors?