AmpSizerHow big does the service need to be?
Adding up every circuit gives a number no house ever reaches. The load worksheet is the arithmetic that turns it into a service size.
One circuit check a month
MonthlyOne thing a month worth measuring, testing or recalculating on a home electrical system — the part of sizing that happens after the install. No product pitches, and nothing that needs a live panel.
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How this works
The standard method, in the order the code applies it
NEC Article 220 Part III for a one-family dwelling, which is what decides the service size.
| Step | What goes in | Factor |
|---|---|---|
| General lighting and receptacles | 3 VA per square foot | 100% of first 10 kVA, 40% of the rest |
| Small appliance branch circuits | 1,500 VA each, minimum two | included in general load |
| Laundry branch circuit | 1,500 VA | included in general load |
| Electric range | Nameplate, per Table 220.55 | demand factors apply |
| Electric dryer | 5,000 VA or nameplate, whichever is greater | 100% |
| Fixed appliances, four or more | Nameplate total | 75% |
| Heating or cooling | The larger of the two | 100% |
The first 10 kVA of general load counts at 100% and everything above it at 40%. That single step is most of the difference between connected load and demand.
Frequently asked questions
What is the difference between connected load and calculated load?
Connected load is everything added up. Calculated load applies the demand factors of Article 220, because a house never runs everything at once — the first 10 kVA of general load counts fully and the remainder at 40%, ranges have their own table, and only the larger of heating or cooling counts. The calculated figure is what sizes the service.
Do I have to use the standard method?
No. Article 220 Part IV gives an optional method for dwellings that is simpler and often gives a smaller answer, and either is acceptable. The standard method is the one most permit applications are laid out for, which is why this sheet follows it.
How much spare capacity should a service have?
Enough for what you will add, which today usually means a charger, a heat pump or an induction range — each of which is 30 to 60 amps of continuous or near-continuous load. Twenty-five percent is a reasonable planning margin. Where the answer will not fit, load management is explicitly recognised by the code and costs a fraction of a service upgrade.