Chargers, a heat pump or a new kitchen line all start with the same question. We read what the facility has actually drawn over a year, add the new load the way the code requires, and give you the answer as fits, tight or short.
Fits, with 40 A to spare on a 400 A service.
The code recognises two ways to establish the load already on a service, and they can give very different answers for the same facility.
A shape, and it describes no particular facility. How much room a measurement shows is a property of the facility.
An Article 220 calculation adds up the equipment and applies demand factors. It has to assume a great deal of that equipment runs at once, because it has no record of what actually did.
NEC 220.87 starts from the highest demand the facility actually recorded over a year. A service that looks full on paper often carries far less than its calculation says.
We use the measured method wherever the facility has operated long enough to have a record, because it is the one that describes the facility as it is.
The existing load is the busiest 15 minutes the service carried in 12 months, read from the utility's own record or, where there is none, from 30 days on the panel.
The 2023 NEC, which California has adopted, adds 125% to the recorded peak. The 2026 edition keeps that margin and numbers the section 120.87. The calculation cites whichever edition the authority reviewing the permit has adopted.
The new load is calculated under the code's own rules for that equipment, at its full rating unless a listed load management system limits it.
We read 12 months of your utility's interval data first, with no visit, and that gives a first answer.
We write the panel down circuit by circuit. Sensors go on only where the utility data cannot settle it.
We add the new load to the measured peak under NEC 220.87 and set the total against your rating.
A licensed Professional Engineer reviews the calculation and seals it for your permit.
The answer from your utility's own data, reviewed by an engineer.
Not sealedThe same answer as a calculation sealed for the permit.
From your utility's recordsWhere the utility cannot see the panel. 30 days measured first.
From 30 days on the panelPreliminary Capacity Report: No seal, so it is not submittable to an AHJ. It is the same analysis and the same numbers, for planning or a second opinion. Upgrade any time and the $500 comes off.
