NEC 220 — Power System Load Calculations Practice Test 1

Question 1: An industrial consumer has a daily load of 3000 kW at 0.8 PF for 12 hours and 2000 kW at unity power factor for 12 hours. The average load power factor is:

• 0.73
• 0.6
• 0.8
• 0.65

Question 2: A single-phase load is connected to a 120 V supply and draws 15 A at a power factor of 0.85. What is the true power (kW) consumed?

• 1.26 kW
• 1.53 kW
• 1.80 kW
• 2.25 kW

Question 3: A balanced 3-phase load is connected to a 480 V (line-to-line) system and draws 20 A per phase at a power factor of 0.9. What is the total three-phase true power?

• 8.64 kW
• 12.47 kW
• 15.0 kW
• 17.28 kW

Question 4: A single-phase transformer secondary delivers 240 V at a full-load current of 50 A. What is the transformer's apparent power rating in kVA?

• 8 kVA
• 10 kVA
• 12 kVA
• 15 kVA

Question 5: A load consumes 8 kW of true power and draws 10 kVA of apparent power. What is the power factor of the load?

• 0.6
• 0.7
• 0.8
• 0.9

Question 6: Per NEC Table 220.42(A), what is the minimum unit load used to calculate the general lighting load for a dwelling unit?

• 2 VA per sq ft
• 3 VA per sq ft
• 3.5 VA per sq ft
• 5 VA per sq ft

NEC Reference: NEC Table 220.42(A)

Question 7: Per NEC 220.52(A), each 20 A small appliance branch circuit in a dwelling unit kitchen area is assigned a load of:

• 750 VA
• 1,000 VA
• 1,500 VA
• 2,000 VA

NEC Reference: NEC 220.52(A)

Question 8: A 1,500 sq ft dwelling has a general lighting load of 4,500 VA. Per NEC Table 220.42(B), what is the demand load after applying the lighting demand factors?

• 2,925 VA
• 3,525 VA
• 4,125 VA
• 4,500 VA

NEC Reference: NEC Table 220.42(B)

Question 9: A power system records 480,000 kWh consumed over 30 days with a maximum demand of 1,000 kW. What is the load factor for the period?

• 48.0%
• 55.0%
• 66.7%
• 75.0%

Question 10: The DEMAND FACTOR of an electrical system is defined as the ratio of:

• Average demand to maximum demand
• Maximum demand to total connected load
• Total kWh consumed to maximum demand
• Reactive power to apparent power

NEC Reference: NEC 220.2

Question 11: A 120 V single-phase branch circuit carries 20 A through 100 ft of 12 AWG copper wire (circular mils = 6,530). Using the formula VD = 2KIL ÷ CM (K = 12.9 for copper), what is the voltage drop?

• 3.9 V
• 5.9 V
• 7.9 V
• 9.9 V

NEC Reference: NEC 210.19(A) Informational Note

Question 12: The power triangle in the diagram shows an apparent power S = 10 kVA and true power P = 8 kW. What is the reactive power Q?

• 2 kVAR
• 4 kVAR
• 6 kVAR
• 8 kVAR

Question 13: A facility draws 80 kW at 0.8 power factor lagging. How many kVAR of capacitors must be installed to correct the power factor to unity (1.0)?

• 40 kVAR
• 50 kVAR
• 60 kVAR
• 80 kVAR

Question 14: Per NEC Table 220.12, what is the minimum unit load (VA per square foot) used to calculate the general illumination load for an office building?

• 2.0 VA per sq ft
• 3.0 VA per sq ft
• 3.5 VA per sq ft
• 5.0 VA per sq ft

NEC Reference: NEC Table 220.12

Question 15: A single-phase transformer is rated 25 kVA, 240V/120V. What is the full-load current on the 120 V secondary?

• 104.2 A
• 150.0 A
• 208.3 A
• 416.7 A

Question 16: A 3-phase transformer bank is rated 150 kVA, 480V/208V. What is the full-load secondary line current?

• 208.3 A
• 360.3 A
• 416.3 A
• 521.6 A

Question 17: Per NEC Table 220.55, what is the demand load for ONE household electric range rated at 12 kW installed in a dwelling unit?

NEC Reference: NEC Table 220.55

Question 18: Per NEC 220.53, what demand factor may be applied to four or more fixed appliances (other than ranges, clothes dryers, or space-heating or air-conditioning equipment) served by the same feeder in a dwelling unit?

• 50%
• 65%
• 75%
• 80%

NEC Reference: NEC 220.53

Question 19: Per NEC 210.20(A), branch-circuit conductors and overcurrent devices must be rated at not less than _______ of the continuous load plus the non-continuous load.

• 100%
• 110%
• 125%
• 150%

NEC Reference: NEC 210.20(A)

Question 20: The circuit diagram shows a 120 V single-phase circuit feeding a load 200 ft away using 10 AWG copper wire (CM = 10,380). The load current is 20 A. Using VD = 2KIL ÷ CM (K = 12.9), what is the voltage drop across the run?

• 4.97 V
• 7.48 V
• 9.94 V
• 14.91 V

NEC Reference: NEC 210.19(A) Informational Note

Question 21: Per NEC 210.19(A) Informational Note No. 4, the maximum recommended voltage drop for a branch circuit (not a mandatory requirement) is:

• 1%
• 2%
• 3%
• 5%

NEC Reference: NEC 210.19(A) Informational Note No. 4

Question 22: The DIVERSITY FACTOR of a power system is defined as:

• Maximum demand divided by total connected load
• Average demand divided by maximum demand
• Sum of individual maximum demands divided by simultaneous maximum demand
• Total kWh divided by maximum demand multiplied by hours

Question 23: A load draws 20 A at 0.8 power factor. Capacitors are added to correct the PF to unity (1.0) while the true power (kW) remains unchanged. What happens to the supply current?

• Increases by 25%
• Decreases by 20% (to 16 A)
• Doubles to 40 A
• Remains unchanged at 20 A

Question 24: Per NEC 220.52(B), the feeder load assigned for each 20 A laundry branch circuit in a dwelling unit is:

• 750 VA
• 1,000 VA
• 1,500 VA
• 2,000 VA

NEC Reference: NEC 220.52(B)

Question 25: A 3-phase motor is connected to a 480 V supply and draws 30 A per phase. A wattmeter reads 20 kW total three-phase power. What is the power factor?

• 0.70
• 0.75
• 0.80
• 0.85

Question 26: Per NEC 220.60, where it is unlikely that two or more noncoincident loads will be used simultaneously, the feeder/service calculation shall include only:

• The smallest load
• The largest load
• The average of all noncoincident loads
• All loads combined at 50% demand

NEC Reference: NEC 220.60

Question 27: The power triangle in the diagram has an apparent power S = 100 kVA at an angle of 36.87° (where cos 36.87° = 0.8). What is the reactive power Q?

• 40 kVAR
• 50 kVAR
• 60 kVAR
• 80 kVAR

Question 28: A facility requires 200 kW of power at a power factor of 0.8 lagging. What is the minimum kVA rating of generator required?

• 160 kVA
• 200 kVA
• 250 kVA
• 320 kVA

Question 29: A dwelling unit has 2,000 sq ft of habitable floor area. Per NEC 220.42, what is the total general lighting load BEFORE applying demand factors?

• 3,000 VA
• 4,500 VA
• 6,000 VA
• 7,500 VA

NEC Reference: NEC 220.42

Question 30: An energy meter in a building reads 3,600 kWh consumed over a 30-day period. What is the average power demand over that period?

• 3 kW
• 5 kW
• 120 kW
• 150 kW