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Dwelling Load Calculation Practice (California Exam)

A dwelling load adds up everything a house can draw, takes the demand discounts code allows, and sizes the service. On the California exam, calculations are part of the Determination of electrical system requirements domain. Here is the pattern, one worked example, and a question to try.

Last reviewed June 2026

One worked example

A 2400 square foot house with a 12 kW range, 5 kW dryer, 15 kW heat, and a 5-ton AC. What service does it need?

  1. 1
    Name the problem

    This is a dwelling service load. We add up everything the house can draw, take the demand discounts code allows, then size the service.

  2. 2
    General loads

    Start with the general loads. Lighting is 3 VA a square foot. Small appliance and laundry circuits are 1500 VA each, with code minimums.

    Lighting: 2400 × 3 = 7200 VA

    Small appliance: 2 × 1500 = 3000 VA

    Laundry: 1 × 1500 = 1500 VA

    Subtotal: 11700 VA

  3. 3
    Apply the demand factor

    Code lets you discount that general subtotal. The first 3000 VA counts full, the rest at 35%.

    First 3000 at 100% = 3000 VA

    Remaining 8700 at 35% = 3045 VA

    Demand-applied: 6045 VA

  4. 4
    Add the big appliances

    Range, dryer, water heater, and the larger of heat or AC. Heat and AC never run together, so you take the bigger one and drop the other.

    Range: 8000 VA

    Dryer: 5000 VA

    Water heater: 0 VA

    Heat vs AC: ac wins at 18000 VA

  5. 5
    Total and service current

    Add it all up, then divide by the service voltage to get amps.

    Total demand: 37045 VA

    Service current = 37045 / 240 = 154.35 A

  6. 6
    Size the service

    The 310.12 rule lets the service conductors carry the load at 83%. Round up to the next standard rating. That puts you at a 150 A service.

    154.35 × 0.83 = 128.11 A

    Next standard rating: 150 A

Now try one

Your turn. An 1800 square foot house, 10 kW range, 5 kW dryer, 4.5 kW water heater, 6 kW AC, no electric heat.

Total it and divide by 240. What's the service current, in amps?

  1. 1
    Total and service current

    Add it all up, then divide by the service voltage to get amps.

    Total demand: 28915 VA

    Service current = 28915 / 240 = 120.48 A

  2. 2
    Size the service

    The 310.12 rule lets the service conductors carry the load at 83%. Round up to the next standard rating. That puts you at a 100 A service.

    120.48 × 0.83 = 100.00 A

    Next standard rating: 100 A

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