Service Upgrade

Notes

• Do not let anyone guess your existing load, including this page. NEC 220.87 gives the real method: take the highest demand recorded in the last 12 months from the utility, multiply by 1.25, and that is your existing load. Most utilities will supply the figure on request; where there is not a year of history, a recording ammeter left on the service for 30 days does the same job. That measured number, plus the 33.3 A above, is the answer.
• 27% of the service goes to this one thing. Whether it fits depends entirely on what the rest of the house already draws. Under 92 A of existing calculated load and it fits; over, and the service has to grow.
• This is not a continuous load, so it counts at its demand figure rather than 125%. Ranges and dryers get further relief in NEC 220.55 and 220.54 because they cycle: a 12 kW range is counted at 8 kW, since the elements are never all on at full for long.
• Load management can save the upgrade, and it is worth pricing first. An EV charger with a load-management device, or an energy-management system that sheds the charger when the range comes on, is a listed and code-recognised way to add a large load to a service that could not otherwise take it. It is frequently a fraction of the cost of a new service.
• A panel swap and a service upgrade are different jobs. If the panel is full but the service is adequate, a subpanel or a panel with more spaces solves it for far less. If the calculated load exceeds the service, new breakers change nothing — the conductors from the utility, the meter base and the mast all have to grow.