Master electrician load calculations
Load calculations are the biggest block of math on the master exam. You add up each type of load at the value Article 220 assigns it, apply the demand factor for that type, and size the service or feeder from the total. Most mistakes come from using the wrong table or forgetting which loads get a demand factor.
A timed 100-question exam in the ICC R16 format on the 2023 NEC, or the two-part Texas exam. Every answer has a worked explanation and you get a score by topic.
Or start with the free load calculations drillDwelling standard method, step by step
- General lighting: 3 VA per square foot of the dwelling’s outside dimensions, excluding open porches, unfinished spaces and garages (220.41 in the 2023 NEC; Table 220.12 in 2020).
- Small-appliance circuits: 1,500 VA for each, with at least two (220.52(A)). Laundry circuit: 1,500 VA (220.52(B)).
- Apply Table 220.42 to the total of those three: the first 3,000 VA at 100%, 3,001 to 120,000 VA at 35%, and the rest at 25%.
- Fastened-in-place appliances other than ranges, dryers, space heating and air conditioning: 75% of nameplate when there are four or more (220.53).
- Clothes dryers: 5,000 W or the nameplate rating, whichever is larger (220.54).
- Ranges, ovens and cooktops: Table 220.55. One range rated 12 kW or less counts as 8 kW; add 5% to Column C for each kW over 12 (Note 1).
- Heating and air conditioning: use only the larger of the two noncoincident loads (220.60).
Worked example: 2,400 ft² dwelling
Standard method with a 12 kW range, 5.5 kW dryer, four fixed appliances and 10 kW of electric heat
- Lighting 2,400 × 3 = 7,200 VA; small-appliance 3,000 VA; laundry 1,500 VA; total 11,700 VA.
- Table 220.42: 3,000 + (8,700 × 35%) = 3,000 + 3,045 = 6,045 VA.
- Range: 12 kW → Column C = 8,000 VA. Dryer: 5,500 VA (nameplate is larger than 5,000).
- Water heater 4,500 + dishwasher 1,200 + disposal 900 + attic fan 600 = 7,200 VA × 75% = 5,400 VA.
- Heat 10,000 VA versus air conditioning 5,000 VA: keep the heat (220.60).
- Total 6,045 + 8,000 + 5,500 + 5,400 + 10,000 = 34,945 VA ÷ 240 V = 145.6 A, so a 150 A service.
Optional methods for dwellings (220.82 and 220.84)
The one-family optional method adds the general loads at nameplate: 3 VA per square foot, 1,500 VA per small-appliance and laundry circuit, and every fastened-in-place appliance, range, dryer and water heater. The first 10 kVA counts at 100% and the remainder at 40%. Then add the largest heating or cooling load from 220.82(C): air conditioning at 100%, or central electric heat at 65%.
For multifamily buildings where each unit has electric cooking and electric heat or air conditioning, 220.84 lets you total every unit’s load and apply one factor from Table 220.84 based on the number of units.
| Dwelling units | Demand factor |
|---|---|
| 3–5 | 45% |
| 6–7 | 44% |
| 8–10 | 43% |
| 11 | 42% |
| 12–13 | 41% |
| 20 | 38% |
| 30 | 33% |
| 40 | 28% |
| 62 and over | 23% |
Practice load calculations under exam time
A timed 100-question exam in the ICC R16 format on the 2023 NEC, or the two-part Texas exam. Every answer has a worked explanation and you get a score by topic.
Or start with the free load calculations drillCommercial loads
- General lighting from Table 220.12 by occupancy, for example 1.3 VA/ft² for offices, 1.9 for retail and 1.2 for warehouses. Lighting is a continuous load, so size the feeder at 125% (215.2(A)(1)).
- Receptacle outlets: 180 VA for each single or multiple receptacle on one yoke (220.14(I)). Table 220.44 lets you take the first 10 kVA at 100% and the rest at 50%.
- Show windows: 200 VA per linear foot (220.14(G)). Each required sign outlet: at least 1,200 VA (220.14(F)).
- Commercial kitchen equipment: Table 220.56 drops to 65% for six or more units, but the result may not be less than the two largest units together.
The 2026 NEC moved and changed these rules
The 2026 NEC moved load calculations from Article 220 to new Article 120 (220.41 became 120.41) and lowered the dwelling general lighting load to 2 VA per square foot. Texas tests the 2026 NEC since September 1, 2026, so a Texas master candidate must work dwelling calculations from the 2026 book. The ICC R16, Michigan and Iowa exams use the 2023 values shown on this page.
Common questions
How many square feet do I use for a dwelling load calculation?
The floor area from the outside dimensions, not counting open porches, garages or unused or unfinished spaces that are not adaptable for future use (Article 220).
When does the 75% appliance demand factor apply?
When a dwelling has four or more fastened-in-place appliances other than ranges, clothes dryers, space heating and air conditioning (220.53).
Do I add heating and air conditioning together?
No. They are noncoincident loads, so you use only the larger of the two (220.60).
Practice load calculations under exam time
A timed 100-question exam in the ICC R16 format on the 2023 NEC, or the two-part Texas exam. Every answer has a worked explanation and you get a score by topic.
Or start with the free load calculations drillMore master exam guides
Section numbers follow the 2023 National Electrical Code (NFPA 70); rules are paraphrased, not quoted. Independent preparation, not affiliated with NFPA, ICC, PSI, Pearson VUE or any state board.