Practice: multifamily optional load calculation
Each problem uses new numbers, so you practice the method rather than memorizing an answer.
Pick the answer: sizes and ratings come from your code book.
Worked solution
Formula
| Symbol | Meaning | Unit |
|---|---|---|
| n | Number of dwelling units | |
| Unit load | Connected load of one unit under 120.84(C) | VA |
| Factor | Table 120.84 demand factor for n units | % |
Worked example
A multifamily building has 46 dwelling units on one service. Every unit has electric cooking and electric heat or air conditioning, and each unit has its own feeder. Each unit's connected load, figured under 120.84(C), is 37.5 kVA. Using the optional method of 120.84, what is the calculated load for the dwelling units, not counting house loads?
- Check 120.84(A): three or more units, electric cooking, electric heat or AC, one feeder per unit. The optional method may be used.
- Total connected load: 46 × 37.5 kVA = 1,725.0 kVA.
- Look up the Table 120.84 demand factor for 46 units: 26%.
- Calculated load: 1,725.0 kVA × 26% = 448.5 kVA.
Answer: 448.5 kVA
Multifamily optional load calculation, explained
Section 120.84 (220.84 in 2023) is the optional method for a feeder or service that supplies three or more dwelling units. It may be used only if no unit is fed by more than one feeder, every unit has electric cooking, and every unit has electric space heating, air conditioning or both. Use it when the question asks for the optional method.
Build each unit's connected load under 120.84(C): 2 VA/ft² for lighting and general-use receptacles, 1,500 VA for each small-appliance and laundry circuit, the nameplate of the range, dryer, water heater and other fastened appliances, motors, and the larger of the air conditioning or the space heat. There is no Table 120.55 and no 5,000 W dryer minimum here.
The 2026 NEC changed the unit load in 120.84(C) from 3 to 2 VA/ft², the same as the one-family rules. The NFPA second draft also relabels the demand table Table 120.84(C), so your book may print it either way. The percentages did not change: 45% for three to five units, falling to 23% for 62 units or more.
Multiply the unit load by the number of units and by the Table 120.84 factor. House loads, such as hallway lighting and a shared laundry, are calculated by the standard method and added on top (120.84(B)).
How to solve it on the exam
- Check the 120.84(A) conditions. If any fails, use the standard method.
- Build one unit's connected load: 2 VA/ft², 1,500 VA per small-appliance and laundry circuit, appliance nameplates, larger of heat or AC.
- Multiply by the number of units.
- Look up the Table 120.84 factor for the total number of units and apply it.
- Add house loads by the standard method, then divide by the system voltage for amperes.
Common mistakes
- Using 3 VA/ft², the 2023 value. The 2026 120.84(C) uses 2 VA/ft².
- Using 8 kW for the range or 5,000 W for the dryer. This method uses nameplates.
- Adding both heat and AC instead of the larger.
- Using the one-family 8 kVA plus 40% rule for an apartment building.
- Applying the factor for the wrong number of units, or applying it to the house loads.
Exam tips
- Table 120.84 is short. Read the row for the exact number of units; the factor only drops 1% every few units.
- Laundry: if the building has a shared laundry room, the units have no laundry circuit, so leave out that 1,500 VA.
Multifamily optional load calculation calculator
Questions people ask
When can I use the multifamily optional method?
When a feeder or service supplies three or more dwelling units, no unit is fed by more than one feeder, every unit has electric cooking, and every unit has electric heat, air conditioning or both (120.84(A)).
Did the multifamily optional method change in 2026?
Yes. It moved from 220.84 to 120.84, and the lighting unit load in 120.84(C) dropped from 3 to 2 VA/ft². The demand percentages are the same.
What is the demand factor for 20 apartments?
38%, from Table 120.84 (18 to 20 units). Check the row in your own code book on exam day.
Sources
- Minnesota DLI: Electrical license examination guide (2026 NEC)
- NFPA: 2026 NEC Second Draft report, Code-Making Panel 2 (Article 120)
About the tables: DLI gives you an untabbed 2026 NEC at the exam. These problems cite the section and table so you practice finding them in the book. We never print NEC text or tables.