Dwelling load calculation (NEC 2026 Article 120)

Guide

In 50 minutes, your students learn to work a standard dwelling load calculation under Article 120: count the floor area, add the circuits, apply the demand factors, and size the service. They also see the optional method.

At a glance

Level: Second-year apprentices
Time: 50 minutes, with a 90-minute variant
Sections: 120.5(C), 120.41, 210.11(C)(1), 120.52(A), 120.52(B), Table 120.45, 120.53, 120.6, 120.51, 120.54, Table 120.55, 120.57, 120.82, Table 120.83, 230.79(C)
Students need: Their own 2026 code book and a calculator
Edition: 2026 NEC
Last checked: October 2026

Class plan by minutes

0 to 5 minWarm-upDraw a 2,000 sq ft house on the board. Ask what loads the service must carry. List their answers and leave them up.
5 to 20 minBoard workWork the standard calculation on the board through the demand factors. Stop after the general load and have students work the first number on paper.
20 to 35 minSimulationPairs play Load Calculation jobs 1 to 3 (Small ranch house, All-electric two-story, Cottage with a basement). Each pair names the demand factor for a line before they drop the tag.
35 to 45 minQuestionsAsk the three quiz questions below, one at a time. Students write an answer alone, then you give the answer and its section. They can use the code book and a calculator.
45 to 50 minWrap-upCheck the warm-up list against the lines of the calculation. Go over the question most students missed.

For a 90-minute block, give the simulation 30 minutes so pairs finish jobs 1 to 4 including the optional method, and use the dwelling service load calculator to check one pair's answer on the projector.

What students learn

By the end of the period, each student can work a standard dwelling load calculation from floor area to service size, name which loads take a demand factor, and say when the 100 A minimum service rule decides the answer.

120.5(C): Measure floor area to the outside of the walls, and leave out detached garages, open porches, and unfinished space that could never become a room.
120.41: Count 2 VA per square foot for lighting and everyday receptacles.
210.11(C)(1): A kitchen needs at least two 20 A small-appliance circuits.
120.52(A): Add 1,500 VA for each small-appliance circuit.
120.52(B): Add 1,500 VA for each laundry circuit.
Table 120.45: Count the first 3,000 VA of the general load at 100%, the rest up to 120,000 VA at 35%, and anything over that at 25%.
120.53: Four or more fixed appliances, each 500 W or ¼ hp and up, may count 75%. Cooking, dryers, heat, air conditioning, and EV chargers stay out of that group.
120.6: Loads that are unlikely to run together, such as heat and air conditioning, count only the largest.
120.51: Fixed electric heat counts at its full connected load.
120.54: A dryer counts its nameplate or 5,000 VA, whichever is larger.
Table 120.55: A household range counts from the table. One range rated up to 12 kW counts 8 kW.
120.57: An EV charger counts its nameplate, or 7,200 VA when there is no nameplate.
120.82: The optional method counts the first 8 kVA at 100% and the rest at 40%.
Table 120.83: Checks whether an existing service has room for new load.
230.79(C): A one-family house never gets a service disconnect under 100 A.

Section numbers only. Read the full text in your code book.

2023 to 2026: our list has 15 changes in Article 120, which was Article 220 in 2023. See the changes

Quiz questions

1. What unit load do you use for lighting and general receptacles when you size the feeder or service for a dwelling?
Answer. 2 VA per square foot. (120.41)
2. The dryer nameplate says 4,000 VA. How many VA do you count for it?
Answer. 5,000 VA, because that is larger than the nameplate. (120.54)
3. A one-family house calculates to 70 amps. What is the smallest service disconnect you can use?
Answer. 100 amps. (230.79(C))

Teaching notes

Before class

Students need their own 2026 code book open to Article 120, and a calculator. Open this lesson and the dwelling service load calculator on your teaching computer before class, and project the lesson. Students can play the simulation on a phone or a laptop. If they have neither, you can project the simulation and have the class choose each drop. Tell students that older books put these rules in Article 220.

How to use the simulation in class

Run it after the board work, so students know which loads take a demand factor.
Pairs take jobs 1 to 3 (Small ranch house, All-electric two-story, Cottage with a basement). Each pair says which line a tag belongs on, and what percent it counts, before they drop it.
Early finishers play jobs 4 to 6 (Optional method, Heat pump and EV charger, Charger on an existing service) to compare the two methods and check an old service.
After a job, have one pair rebuild the same house in the dwelling service load calculator and compare totals. When the totals differ, find the line that is off.

Two discussion questions

1. A house calculates to 70 A on paper. A customer asks why you quoted a 100 A service. What do you say?
Look for: A one-family house gets a service disconnect of at least 100 A, even when the calculation comes out lower (230.79(C)). Students should also say the calculation is the minimum load, not a design goal.
2. The same house comes out smaller with the optional method. Why might you still run the standard method first?
Look for: The standard method shows every line and every demand factor, so you can see which loads drive the total (Part III). The optional method is allowed when the service is 120/240 V or 208Y/120 V, 3-wire, and 100 A or more (120.82(A)). Look for students who see that both are allowed and the inspector may expect one.

Mistakes to watch for

Counting an open porch or a detached garage in the floor area.
Adding lighting and receptacles on top of the 2 VA per square foot.
Giving a dryer or a range the 75% fixed-appliance factor.
Using the dryer nameplate when it is under 5,000 VA.
Adding both heat and air conditioning when they cannot run together.
Rounding an answer down to a service size below 100 A.

If a student’s book is a different edition

This lesson follows the 2026 NEC, where load calculations sit in Article 120. In the 2023 book and earlier, they sit in Article 220, and the dwelling minimum unit load was 3 VA per square foot. In the 2026 book, 120.13 still keeps 3 VA per square foot for counting how few branch circuits a house needs. If a student has an older book, tell them to find the same topic and compare, and to check which edition your authority having jurisdiction enforces.

Questions people ask

Where did the dwelling load calculation rules go in the 2026 NEC?

They moved from Article 220 to Article 120. The standard method for feeders and services is in Part III, and the optional method is in Part IV (120.80).

How much do I count for lighting and receptacles in a house?

2 VA per square foot of floor area, measured from the outside of the walls and leaving out open porches, detached garages, and unfinished space that could never become a room (120.41, 120.5(C)).

Which loads can take the 75% fixed-appliance factor?

Four or more fixed appliances, each 500 W or ¼ hp and up, can. Cooking equipment, dryers, space heating, air conditioning, and EV chargers do not (120.53).

What is the smallest service for a one-family house?

100 A, even when the calculation comes out lower (230.79(C)).

Ask Shorty is independent and is not affiliated with NFPA. Check every answer against your adopted code and your authority having jurisdiction. This lesson follows the 2026 NEC and was last checked October 2026. See something wrong? Tell us and we will check it against the code.