NEC Article 220 Dwelling Load Calculations

Pick the method before the math

Article 220 gives more than one dwelling path. The standard method builds the load piece by piece. The optional method has different buckets and different demand treatment. Both can be valid when the installation qualifies. The exam point is that you cannot mix them.

If you want to check arithmetic after the setup, use the free dwelling load calculator. If you are studying for the exam, learn the order first.

Standard method sequence

1. General lighting load: living area x 3 VA per square foot.
2. Small-appliance circuits: include the required 1,500 VA circuits.
3. Laundry circuit: include the required 1,500 VA circuit.
4. Apply the dwelling demand factor to that subtotal.
5. Add range demand from the range table, not the raw nameplate unless the table tells you to.
6. Add dryer demand using at least 5,000 VA or the nameplate if larger.
7. Add fixed appliances and other loads as the question gives them.
8. Compare heat and AC. Use the larger one and drop the smaller.
9. Divide total VA by the service voltage to get amps.

Worked example: 2,400 square foot house

A 2,400 sq ft dwelling has a 12 kW range, 5,000 VA dryer, 4,500 VA water heater, 9,600 VA electric heat, and 6,000 VA air conditioning. Use the standard method sequence.

1. Lighting: 2,400 sq ft x 3 VA = 7,200 VA.
2. Small-appliance circuits: 2 x 1,500 VA = 3,000 VA.
3. Laundry circuit: 1,500 VA.
4. General subtotal: 7,200 + 3,000 + 1,500 = 11,700 VA.
5. Demand on that subtotal: first 3,000 VA at 100%, remainder 8,700 VA at 35%, for 6,045 VA.
6. Range: one 12 kW range commonly points to 8,000 VA demand from the range table.
7. Dryer: 5,000 VA.
8. Water heater: 4,500 VA.
9. Heat vs AC: use 9,600 VA heat and drop the 6,000 VA AC.
10. Total: 6,045 + 8,000 + 5,000 + 4,500 + 9,600 = 33,145 VA.
11. Amps at 240 V: 33,145 / 240 = 138.1 A before selecting the service rating.

The 83% conductor allowance is not the load calculation

The dwelling conductor allowance in Article 310 is a conductor sizing step. It is not how you calculate the dwelling load. First calculate the load, then select the service or feeder rating, then check whether the conductor rule applies to that installation.

This matters because candidates sometimes multiply the calculated load by 83% and call it done. That is the wrong order.

Wrong answers the exam wants you to pick

Leaving out the required circuits

The two small-appliance circuits and the laundry circuit are easy to forget because they are not tied to square footage. They still belong in the load.

Using range nameplate without checking the table

A household range question usually sends you to the range demand table. The nameplate is the starting clue, not always the final demand.

Adding heat and AC together

Heat and air conditioning do not run as full noncoincident loads at the same time. Use the larger one unless the question gives a special condition that changes the rule.

Mixing standard and optional methods

If the problem asks for the optional method, run that method. If it asks for the standard method, run that method. A hybrid answer is not safer. It is just wrong in two directions.

How to drill this for the exam

Write the buckets before you solve: square feet, small appliance, laundry, range, dryer, fixed appliances, heat or AC, service amps. Then place every number from the question into one bucket. Empty buckets are fine. Numbers floating loose are where points disappear.