sparkytools

Fourth year Services · tool

Load calculation helper

Walk the load-calculation method step by step: the basic load from floor area, the demand factors on it, the other loads with their own factors, then total demand and amps. Every factor is one you type in from your own code book.

Every factor here comes from YOUR code book — the defaults are practice numbers, not code values. Replace them before you rely on the answer.

2 · Basic load method
3 · Demand on the basic load (leave the first size blank for none)
4 · Other loads, each with its own demand %
5 · Supply
  • Basic load (connected)—
  • Basic load after demand—
  • Other loads, connected → after demand—
  • Total connected—
  • Total demand—
  • Calculated current—
Show the working

    Arithmetic on the values you entered. It does not choose a service size or say whether anything complies — your code book’s rules, the minimums it sets, and your inspector decide that.

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    How the method goes

    1. Floor area. Measured the way your book defines it.
    2. Basic load. Area × a load per unit area, or a first block plus a load for each additional block — from your book, for the occupancy.
    3. Demand on the basic load. Your book may let the first slice count in full and later slices at a lower percentage.
    4. Other loads. Ranges, heat, air conditioning, water heaters, dryers, EV chargers — each at the demand your book gives it, sometimes depending on the others (heat versus air conditioning, for example).
    5. Total and amps. Add the demand figures; divide by the voltage (× √3 for three-phase). Then compare against the minimums and rules in your book — that part is yours.

    Worked: the default practice numbers (not code values)

    1. Basic load: 1500 ft² × 4 VA = 6,000 VA.
    2. Demand: the first 5,000 VA at 100% = 5,000; the next 1,000 VA at 40% = 400. Basic after demand = 5,400 VA.
    3. Other loads: range 10,000 × 60% = 6,000; water heater 4,000; dryer 5,000. After demand = 15,000 VA.
    4. Total demand = 5,400 + 15,000 = 20,400 VA. At 240 V single-phase: 20,400 ÷ 240 = 85 A.

    Questions people ask

    Why doesn’t this tool fill in the code values for me?

    Because they belong to your code book, and they change. The basic load per unit of area, the block sizes, the demand factors and which loads get which factor are set by CSA C22.1 in Canada and the NEC in the US, differ between dwelling and commercial occupancies, and get revised every cycle. Typing them in from your own book keeps the answer right for your jurisdiction and your edition — and it is exactly what the exam asks you to do.

    What is the difference between connected load and demand load?

    Connected load is everything added up as if it all ran at once at full rating. Demand load recognises that it never does — the range is not on full while the dryer, the heat and every light are — and applies the factors the code allows to get a realistic figure to size the service from.

    Which method — rate × area or blocks?

    Whichever your code book uses for the occupancy. Some methods give a load per square foot or square metre; others give a fixed load for a first block of floor area and a smaller one for each additional block. Pick the one that matches your book and type its numbers in.

    Can I use it for three-phase?

    Yes — choose three-phase and enter the line-to-line voltage. The amps come out as demand VA ÷ (√3 × V), which assumes the load is spread evenly across the three phases.

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