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TDLR dwelling load practice

A dwelling load adds up everything a house can draw, takes the demand discounts code allows, and sizes the service. This is a TDLR Calculations-part question type, now scored on its own. Here is the pattern, one worked example, and an original 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

Try an original question

Sample question · original

A dwelling has 9,000 VA of general lighting and small-appliance load. Apply the standard demand factor: the first 3,000 VA at 100%, the remainder at 35%.

What is the demand load?

  • A3,150 VA
  • 5,100 VA
  • C9,000 VA
  • D7,200 VA

Answer B. First 3,000 VA at 100% is 3,000. The remaining 6,000 VA at 35% is 2,100. Total demand is 3,000 + 2,100 = 5,100 VA (Table 220.45).

  • NEC 2023 Table 220.45
  • NEC 2023 220.42

Why the other answers tempt you

  • A: 3,150 VA applies 35% to the entire 9,000. The first 3,000 still counts at full value.
  • C: 9,000 VA applies no demand factor at all. That is the connected load, not the demand load.
  • D: 7,200 VA discounts the remainder at 70% instead of 35%.

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