NEC service upgrade load calculator (220.83 and 220.87)

Enter the existing service, the size of the home, the existing appliances and the new loads (for example a 48 A EV charger) and we show whether the existing main breaker is enough under the NEC: by the calculated method (220.83) and, if you have measured data, the measured method (220.87), with the suggested service and conductor and the working line by line. An informative calculation; NEC mode is in beta.

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What does the service upgrade calculator calculate?

For upgrading the service of an existing US dwelling (for example for an EV charger, a heat pump or an air conditioner) it shows whether the existing main breaker is enough under the NEC and, if not, what service and conductor are needed. It compares two methods:

• Calculated load (NEC 220.83): from the existing general load of the home (3 VA/ft² general lighting, small-appliance and laundry circuits, the fixed appliances you enter) and the new loads. The first 8 kVA count at 100 %, the rest at 40 %. If the new loads include heating or cooling, 220.83(B) applies and the larger of heating and cooling counts separately at 100 %; otherwise the method is 220.83(A).
• Measured load (NEC 220.87): if you enter the measured maximum demand (A at 240 V; from the last year or a 30-day recording), the program takes 125 % of it and adds the new load (continuous loads at 125 %).

For both methods you see the total load (VA), the current at 240 V, whether the existing service is enough, the suggested service and conductor when it is not, and the working for every line. The 48 A EV charger button adds an 11,520 VA continuous load.

When do the two results differ?

The calculated method estimates from the size of the home and its appliances, the measured method comes from actual use, so the results can differ, and the measured data often gives the more favourable result. Which one is acceptable is decided by the authority having jurisdiction (AHJ).

What does it not calculate?

The service upgrade calculator is for single-phase, three-wire 120/240 V dwellings, and above 200 A it only indicates that an engineered design is needed. You must check the conditions of 220.87 yourself (the 30-day recording must cover the heating and cooling season; with solar or peak shaving the measurement cannot be used). It is an informative calculation, not a permit document: compliance is decided by the authority having jurisdiction (AHJ) and the NEC edition in force, and the values must be checked against the official text. The program's NEC mode is in beta.

Related calculators

For the dwelling load without new loads use the NEC load calculator; the circuits and the board (load center, panel schedule) are shown on the panel schedule maker page. For the whole plan see the US electrical plan page.

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