Power System Load Calculations (NEC 220) — NEC 2020 Edition

Question 1: A plant has a daily load of 3,000 kW at 0.8 power factor for 12 hours, and 2,000 kW at unity power factor for the other 12 hours. What is the average load power factor?

• 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 consumed?

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

Question 3: A balanced 3-phase load on a 480 V system 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 apparent power rating?

• 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 its power factor?

• 0.6
• 0.7
• 0.8
• 0.9

Question 6: Per NEC Table 220.12, 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 220.12

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

• 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 connected load of 4,500 VA. Per NEC Table 220.42, 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

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?

• 48.0%
• 55.0%
• 66.7%
• 75.0%

Question 10: The demand factor of an electrical system is defined as the ratio of what?

• 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 Article 220

Question 11: A 120 V single-phase branch circuit carries 20 A through 100 ft of 12 AWG copper wire (6,530 circular mils). Using VD = (2 x K x I x L) / CM with 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: A power triangle has an apparent power S = 10 kVA and a 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?

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

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

• 1.3 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?

• 8 kW
• 12 kW
• 6 kW
• 10 kW

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, dryers, or space-heating/AC 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 what percent of a continuous load, plus 100% of any non-continuous load?

• 100%
• 110%
• 125%
• 150%

NEC Reference: NEC 210.20(A)

Question 20: A 120 V single-phase circuit feeds a load 200 ft away using 10 AWG copper wire (10,380 circular mils), drawing 20 A. Using VD = (2 x K x I x L) / CM with K = 12.9, what is the voltage drop?

• 4.97 V
• 7.48 V
• 9.94 V
• 14.91 V

NEC Reference: NEC 210.19(A) Informational Note

Question 21: Per the NEC 210.19(A) informational note, what is the maximum RECOMMENDED (not mandatory) voltage drop for a branch circuit?

• 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 what?

• 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 times hours

Question 23: A load draws 20 A at 0.8 power factor. Capacitors correct the power factor to unity while true power stays the same. 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), what feeder load is assigned for each 20 A laundry branch circuit in a dwelling unit?

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

NEC Reference: NEC 220.52(B)

Question 25: A 3-phase motor on a 480 V supply draws 30 A per phase, and a wattmeter reads 20 kW total. 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 loads will run at the same time, what must be included in the feeder or service calculation?

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

NEC Reference: NEC 220.60

Question 27: A power triangle has an apparent power S = 100 kVA at an angle where cos(angle) = 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 generator kVA rating 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 Table 220.12, what is the general lighting load BEFORE demand factors are applied?

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

NEC Reference: NEC Table 220.12

Question 30: An energy meter 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