Minimum service size, including 100 A for homes
A service disconnect must be rated for at least the calculated load. The minimums are 100 A for a one-family home, 60 A for most other installations, 30 A for up to two 2-wire circuits, and 15 A for a single branch circuit.
What the code requires
The service disconnect's rating must be at least the load calculated under Article 220 (Part III, IV or V), and it can never be below the minimums in 230.79(A) through (D).
The minimums are 15 A for an installation with a single branch circuit; 30 A for no more than two 2-wire branch circuits; 100 A, 3-wire, for a one-family dwelling; and 60 A for all other installations.
The minimum is a floor, not a target. If the load calculation comes out higher, the disconnect must be rated for the larger number.
On the job
- A new single-family service rated below 100 A is a correction.
- A service rating that does not cover the Article 220 calculated load is a correction, even if it meets the minimum.
- Disconnects at detached buildings follow the same minimum ratings under 225.39.
In California
California does not amend this section. Separately, CEC 706.10 points to Energy Code 150.0(s), which sets battery-storage readiness, including a minimum panelboard busbar rating, for newly built single-family buildings (one or two dwellings) with service over 125 A, unless a battery system is installed.
Related sections
- NEC 220.83: Adding new loads to an existing home's service
- NEC 220.87: Using actual demand data to size added load
- NEC 225.39
- NEC 230.42: Sizing service-entrance conductors
Where this comes from
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Kyle Robert Anderson KBC Electric · CSLB #1073066 · C-10 Electrical · Licensed since 2021