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Electrical Service Sizing Calculation Practice Test 2026
- A single-family dwelling has a total connected load of 24 kW. What minimum service rating is required according to NEC 2026? A) 100 A B) 125 A C) 150 A D) 200 A The minimum service rating is determined using 125% of continuous load plus 100% of non-continuous load per NEC service sizing rules.
- A dwelling unit has a calculated load of 36 kW. Which service size is most appropriate? A) 100 A B) 150 A C) 200 A D) 250 A NEC requires rounding up to the next standard service size.
- A small office has a total calculated load of 45 kW at 208Y/120 V. What size service in amperes is required? A) 100 A B) 150 A C) 200 A D) 225 A Use the formula: I = Load ÷ Voltage × √3 for three-phase systems.
- For a 3-phase 480 V service supplying a 30 kW load, what is the minimum service ampacity? A) 30 A B) 36 A C) 36.1 A D) 50 A Three-phase current: I = P ÷ (√3 × V × PF), assuming PF = 1.
- A dwelling has a 2400 sq ft area. NEC 2026 general lighting load factor is 3 VA/sq ft. What is the general lighting load? A) 6.5 kW B) 7.2 kW C) 7.5 kW D) 8 kW Lighting load = Area × VA/sq ft.
- A commercial service with 120 kW calculated load at 208 V, 3-phase, requires what service amperage? A) 250 A B) 300 A C) 333 A D) 400 A Three-phase amperage formula: I = P ÷ (√3 × V).
- A dwelling with 3 kW small appliance load, 1.5 kW general lighting, and 5 kW range requires what minimum service rating? A) 60 A B) 100 A C) 125 A D) 150 A Sum all loads and apply NEC demand factors.
- If a dwelling has a 50 kW calculated load, what is the minimum service size? A) 150 A B) 175 A C) 200 A D) 225 A NEC requires standard sizing rounded up to nearest standard rating.
- A 208Y/120 V office building load is 36 kW, power factor 0.9. Minimum service ampacity? A) 115 A B) 116 A
14.A small retail store has a 60 kW load at 480 V, 3-phase. Required service amps? A) 72 A B) 72.2 A C) 75 A D) 80 A Three-phase calculation: I = P ÷ (√3 × V). 15.A dwelling has 4 kW lighting, 6 kW small appliances, and 3 kW general loads. Minimum service rating? A) 100 A B) 125 A C) 150 A D) 175 A Apply NEC dwelling demand factors. 16.A 208Y/120 V, 3-phase office building has 50 kW total load. Required service amperage? A) 125 A B) 138 A C) 139 A D) 150 A I = P ÷ (√3 × V). 17.A residential service has 12 kW load continuous. Applying 125% factor, required amperage? A) 50 A B) 62.5 A C) 63 A D) 75 A 12 kW × 1.25 ÷ 240 V = 62.5 A, rounded to next standard. 18.For a dwelling unit, a 5 kW range and 3 kW dryer. NEC demand factor applied gives total demand 7.5 kW. Minimum service size? A) 60 A
B) 75 A
C) 100 A
D) 125 A
Demand factors reduce sum of appliances. 19.A service is 480 V, 3-phase, load 80 kW, PF 0.95. Minimum service amps? A) 100 A B) 97 A C) 105 A D) 110 A I = P ÷ (√3 × V × PF). 20.Single-phase 240 V dwelling with 24 kW calculated load. Service required? A) 80 A B) 100 A C) 125 A D) 150 A I = 24,000 ÷ 240 = 100 A; continuous load factor applied. 21.NEC requires service conductors for dwelling to be sized for: A) 100% of calculated load B) 125% of continuous load C) 125% of continuous + 100% non-continuous load D) 150% of total connected load NEC 2026 Section 230.42. 22.A dwelling has 15 kW total calculated load. Minimum standard service size? A) 100 A B) 125 A C) 150 A D) 175 A Standard service size selection based on NEC. 23.For a three-phase service of 60 kW at 208 V, what is the ampacity? A) 166 A
28.A 3-phase, 208 V office has a total load 24 kW. Service amps? A) 66.7 A B) 66.5 A C) 70 A D) 75 A I = P ÷ (√3 × V). 29.A dwelling with 3 kW lighting, 6 kW small appliances, 5 kW range. NEC 2026 minimum service? A) 100 A B) 125 A C) 150 A D) 175 A NEC demand factors applied. 30.A small commercial building has 36 kW load at 480 V 3-phase. Minimum service? A) 43 A B) 43.3 A C) 43.3 A D) 50 A I = P ÷ (√3 × V). 31.For dwellings, NEC 2026 allows optional service rating reduction for: A) Appliances less than 2 B) Small appliance and laundry loads per Table 220. C) Lighting only D) None Optional reduction uses NEC Table 220.55. 32.A 240 V, single-phase service load 10 kW. Minimum service ampacity? A) 40 A B) 50 A C) 42 A
D) 60 A
I = P ÷ V.
33.A dwelling has 120 A service, 18 kW load. Is service adequate? A) Yes B) No C) Only if continuous < 12 kW D) Only if demand factor applied 125% continuous load requirement met. 34.NEC service conductors must be sized for: A) Continuous load only B) Non-continuous load only C) Continuous + non-continuous load per Section 230. D) 150% total connected load 230.42 specifies this. 35.A dwelling has 2 appliances totaling 8 kW. NEC demand factor applied load? A) 8 kW B) 7 kW C) 6.4 kW D) 5.5 kW Table 220.55 reduces load.
- 3 - phase, 208 V service supplying 36 kW. Minimum amps? A) 100 A B) 101 A C) 100.1 A D) 110 A I = P ÷ (√3 × V). 37.For single-family dwelling, NEC minimum service voltage? A) 120/240 V B) 120/208 V C) 120/240 V single-phase
D) 150% total load Per Section 230.42. 43.A 208Y/120 V, 3-phase service with 36 kW load. Minimum amps? A) 100 A B) 101 A C) 100.1 A D) 110 A I = P ÷ (√3 × V). 44.Dwelling has 2 kW lighting, 4 kW small appliance, 3 kW laundry. NEC demand? A) 8 kW B) 7 kW C) 6.6 kW D) 7.5 kW Table 220.55 applied. 45.A dwelling with 3 appliances, total 12 kW. NEC demand load? A) 10 kW B) 10.8 kW C) 11 kW D) 12 kW Demand factor reduces sum per NEC. 46.A 240 V dwelling load 20 kW. Minimum service? A) 100 A B) 125 A C) 125 A D) 150 A I = P × 1.25 ÷ V.
- 3 - phase, 480 V, 60 kW load. Minimum amps? A) 70 A B) 72.2 A
C) 72.1 A
D) 75 A
I = P ÷ (√3 × V).
48.NEC 2026 recommends optional service reduction for dwellings with: A) Large appliances only B) Fewer than 4 small appliances C) Lighting only D) None Per Section 220.55. 49.Single-phase, 240 V, 15 kW continuous load. Service rating? A) 60 A B) 75 A C) 80 A D) 100 A 125% applied to continuous load. 50.A dwelling with 24 kW total load, continuous 18 kW, non-continuous 6 kW. Minimum service? A) 100 A B) 125 A C) 150 A D) 175 A I = (1.25 × continuous + non-continuous) ÷ 240 V. This completes the first 50 questions of the Electrical Service Sizing Calculation Practice Test 2026 , with correct answers highlighted and explanations in italics , following NEC 2026 standards. I can prepare questions 51– 100 in the same format to complete the full 100- question mock exam. Do you want me to continue? 51 – 100
D) 125 A
Per NEC Section 230.79. 55.A small commercial building 480 V 3-phase, 90 kW load, PF 0.95. Minimum service amps? A) 108 A B) 108.7 A C) 110 A D) 120 A I = P ÷ (√3 × V × PF). 56.A dwelling has 12 kW calculated load. Minimum standard service size? A) 100 A B) 125 A C) 150 A D) 175 A Round up to the next standard size. 57.A 208 V, 3-phase office has 24 kW load. Service amps? A) 66 A B) 66.5 A C) 67 A D) 70 A I = P ÷ (√3 × V). 58.A dwelling with 18 kW load, continuous 12 kW, non-continuous 6 kW. Minimum service amps? A) 125 A B) 150 A C) 175 A D) 200 A I = (1.25 × 12 kW + 6 kW) ÷ 240 V = 150 A. 59.NEC 2026 requires service conductors sized for: A) Continuous load only
B) Non-continuous only C) Continuous + non-continuous D) 150% total connected load Section 230.42. 60.Single-phase 240 V, 15 kW continuous load. Service rating? A) 60 A B) 75 A C) 80 A D) 100 A 125% of continuous load: 15 × 1.25 ÷ 240 = 78.1 A → round to 75 A. 61.A 480 V 3-phase, 60 kW load, PF 0.9. Minimum amps? A) 76 A B) 77 A C) 76.2 A D) 80 A I = P ÷ (√3 × V × PF). 62.Dwelling 10 kW lighting, 6 kW small appliance, 4 kW laundry. NEC demand load? A) 18 kW B) 17 kW C) 16 kW D) 15 kW Demand factors applied to reduce total. 63.208Y/120 V, 3-phase, 50 kW load. Minimum service amps? A) 138 A B) 139 A C) 140 A D) 145 A I = P ÷ (√3 × V).
69.Single-phase 240 V, 10 kW continuous load. Minimum service? A) 40 A B) 50 A C) 52 A D) 60 A I = 10 × 1.25 ÷ 240 = 52.1 A. 70.NEC 2026 recommends optional service reduction for dwellings with: A) Large appliances only B) Fewer than 4 small appliances C) Lighting only D) None 71.A 208Y/120 V office 36 kW load, PF 0.9. Service amps? A) 115 A B) 116 A C) 120 A D) 125 A I = P ÷ (√3 × V × PF). 72.A dwelling has 24 kW total load. Standard service size? A) 125 A B) 150 A C) 175 A D) 200 A Continuous + non-continuous considered. 73.NEC requires conductors sized for: A) Only continuous B) Only non-continuous C) Continuous + non-continuous D) 150% total load
- 3 - phase, 480 V, 50 kW load. Minimum service amps? A) 60 A
B) 61 A
C) 60.2 A
D) 65 A
I = P ÷ (√3 × V).
75.A dwelling with 15 kW load. Minimum standard service rating? A) 125 A B) 150 A C) 175 A D) 200 A 76.Single-phase 240 V, 12 kW continuous load. Service amps? A) 60 A B) 62.5 A C) 63 A D) 65 A I = 12 × 1.25 ÷ 240. 77.A small office, 208Y/120 V, 36 kW load. Service amps? A) 99 A B) 100.1 A C) 102 A D) 105 A 78.NEC Table 220.55 allows demand factor for: A) Only lighting B) Only laundry C) Appliances in dwelling D) None 79.A dwelling has 3 appliances totaling 12 kW. NEC demand load? A) 10 kW B) 10.8 kW C) 11 kW D) 12 kW
86.Dwelling with 2 appliances totaling 8 kW. NEC demand factor load? A) 8 kW B) 7 kW C) 6.4 kW D) 5.5 kW 87.Single-phase 240 V, 15 kW continuous load. Service size? A) 60 A B) 75 A C) 80 A D) 100 A 88.208Y/120 V 3-phase, 50 kW load. Minimum service? A) 138 A B) 139 A C) 140 A D) 145 A 89.NEC service conductors sized for: A) Continuous only B) Non-continuous only C) Continuous + non-continuous D) 150% total 90.A dwelling has 24 kW total load. Minimum service rating? A) 125 A B) 150 A C) 175 A D) 200 A 91.480 V 3-phase, 80 kW load, PF 0.95. Minimum amps? A) 96 A B) 97 A C) 96.7 A D) 100 A
92.Single-phase 240 V, 10 kW continuous load. Service amps? A) 40 A B) 50 A C) 52 A D) 60 A 93.NEC optional service reduction applies when: A) Only lighting B) Only large appliances C) Fewer than 4 small appliances D) None 94.208Y/120 V, 3-phase, 36 kW load, PF 0.9. Minimum amps? A) 115 A B) 116 A C) 120 A D) 125 A 95.Single-phase 240 V, 20 kW continuous load. Minimum service? A) 100 A B) 125 A C) 125 A D) 150 A 96.A dwelling has 12 kW calculated load. NEC standard service size? A) 100 A B) 125 A C) 150 A D) 175 A
- 3 - phase 480 V, 50 kW load, PF 0.9. Service amps? A) 60 A B) 61 A C) 60.2 A D) 65 A
