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Building Code Reference

Got a CEC 230.79 correction?

Service disconnect panel size

For builders in California, Greater Seattle, the Las Vegas area, the Denver area and Kansas City · CrossBeam Permits

What this code requires, how to fix it, and how cities and counties review it

What this code requires

CEC 230.79 is the California Electrical Code section that sets the minimum ampacity rating for a service disconnecting means. The disconnect must be rated for at least the calculated load it serves, with specific floors: 100 amps for a one-family dwelling, 30 amps when the service supplies only two branch circuits, 15 amps for a single branch circuit, and 60 amps for all other installations. Most new single-family homes and ADUs require 200-amp service because modern electrical loads — EV charging, heat pumps, electric ranges, and multiple HVAC systems — routinely push calculated demand above the 100-amp floor.

How to fix it

  1. Pull the Article 220 load calculation and verify the total

    Start with the load calculation worksheet — this is the document that justifies the service size. Add up all the general lighting loads (3 VA per sq ft minimum), small appliance branch circuits (1500 VA each), laundry circuit, and all fixed appliances at their nameplate values. Then apply the demand factors from CEC Article 220 for electric heat or air conditioning (use the larger load, not both). If you're adding an EV charger, include it at 7,200 VA or its nameplate rating, whichever is larger, per CEC 220.57. The sum of all loads, after demand factors, is your minimum required service rating.

  2. Confirm the disconnect ampacity meets or exceeds the calculated load

    CEC 230.79 requires the service disconnecting means rating to be not less than the calculated load from Article 220, and not less than 100 amps for a single-family dwelling. If your load calculation comes in at 120A, the disconnect must be rated 125A or 200A — whatever the next standard size is above your calculated load. A 100A disconnect on a 120A calculated load fails 230.79 regardless of what the utility meter allows. Standard residential service sizes are 100A, 150A, 200A, and 400A. Most new construction goes to 200A.

  3. Label the main disconnect on the single-line diagram

    The single-line diagram on your electrical plans must show the main disconnect with its ampacity rating called out explicitly. Write it as 'Main Disconnect: 200A, 240V, 2-pole' on the diagram. Don't rely on the panel schedule alone — plan-checkers review the single-line first, and if the rating isn't there, they flag 230.79 before they ever open the schedule. If you're using a meter-main combo unit, label it as such and note the main breaker rating separately from the meter rating.

  4. Show the service entrance conductor sizing on the plans

    The service entrance conductors feeding the disconnect must be sized to match the service rating. For a 200A service, that's typically 4/0 AWG aluminum or 2/0 AWG copper for the ungrounded (hot) conductors, per CEC Table 310.12. Show the conductor sizing on the single-line diagram or in a conductor schedule on your plans. If the service entrance conductors are undersized for the disconnect rating, you'll pick up a separate CEC 230.31 correction on top of the 230.79 flag.

  5. For ADU or detached structure feeders, show the sub-panel disconnect separately

    If the correction is on an ADU or detached garage served from the main house panel, you need a separate disconnect at the sub-panel location per CEC 225.32. That disconnect must also be rated for the calculated ADU load. Show the ADU load calculation on the plans and label the sub-panel disconnect ampacity. A typical ADU with standard appliances needs a 60A or 100A disconnect at the structure — show that rating explicitly rather than just writing 'sub-panel per code.'

  6. Revise the permit scope if a service upgrade is required

    If the load calculation shows you need to upgrade from 100A to 200A service, that upgrade has to appear in the permit scope. Call the utility (SCE in most OC jurisdictions, or Anaheim Public Utilities in parts of Anaheim) to verify the transformer has capacity for the upgraded service, and include their approval letter or service order number in your plan set if the AHJ asks for it. The permit should list 'electrical service upgrade to 200A' explicitly. A service upgrade often requires a separate inspection by the utility company before the city does their final.

  7. Resubmit with a response letter citing the updated sheets

    When you resubmit, include a correction response letter that specifically references the 230.79 correction item and points to the sheet and detail number where you addressed it. Something like: 'Correction 4 (CEC 230.79): See Sheet E1.0, revised single-line diagram — main disconnect rated 200A, load calculation attached as E1.2 showing 165A calculated demand.' Checkers review dozens of plan sets; making it easy to find your response gets you out of the queue faster.

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Why you got flagged

Plan-checkers flag CEC 230.79 most often when the electrical plans don't show the service panel ampacity at all. The single-line diagram or panel schedule needs to call out the main disconnect rating explicitly. If that box is blank or the sheet just says "200A panel, see specs," a checker has no way to verify the disconnect is rated for the calculated load without hunting through a separate document — and most won't do that hunting.

The second common trigger is undersized service on projects that added significant new electrical loads after the original permit was filed. A home originally served by a 100-amp panel passes the 230.79 floor, but once the plans call for a Level 2 EV charger (typically 50A dedicated circuit), a heat pump water heater (30A), and electric cooking (40-50A), the Article 220 load calculation often comes in above 100 amps. If the engineer didn't revise the service to 200A or document a demand factor, 230.79 flags automatically.

Accessory Dwelling Unit projects hit this correction for a different reason. When an ADU is served from the main house panel as a feeder, the checker applies Article 225 and 230.79 together: the disconnect for the ADU sub-panel must still be rated for the calculated ADU load, and the main house panel must have enough headroom to carry both. If the load calculation shows combined demand over 200A, the existing service is under-rated and the correction cites 230.79 directly.

Remodel and addition permits flag it when the contractor sized the service based on the original build rather than the post-addition load. Adding a 400 sq ft addition with a mini-split, two bathrooms, and a kitchen upgrade bumps the Article 220 calculated load enough that a 100-amp service no longer qualifies. The fix is a revised load calculation showing the new demand and, if needed, a service upgrade to 200A or 400A.

The official code

California Electrical Code (Title 24 Part 3) — Article 230 Services, Section 230.79

Read the source →

Common questions

What is the minimum service size for a single-family home under CEC 230.79?
100 amps is the absolute floor for a single-family dwelling under CEC 230.79. But 100 amps is rarely enough for new construction or major remodels. Once you add a Level 2 EV charger (typically 50A), a heat pump water heater (30A), and electric cooking (40-50A), the Article 220 load calculation usually lands between 120A and 180A, which means you need 200A service. Most building departments in Orange County expect 200A on new single-family permits and will push back on anything smaller without a detailed load calc showing why 100A or 150A is sufficient.
Does CEC 230.79 apply to ADU permits?
Yes. An ADU counts as a separate dwelling unit, so the disconnect serving it must meet the 230.79 requirements for a one-family dwelling — minimum 100A if it has its own service, or sized to the calculated ADU load if fed from the main house panel. In practice, most ADU corrections on 230.79 come up when the ADU sub-panel disconnect isn't labeled with an ampacity rating, or when the combined load calc for the main house plus ADU exceeds the existing service capacity. If you're adding an ADU to a house with 100A service and the combined load calc pushes above 100A, the correction will cite both 230.79 and Article 225.
Can I use a 100-amp disconnect on a 200-amp service?
No. CEC 230.79 requires the disconnect to be rated for the calculated load, and that calculated load is what justifies a 200A service in the first place. If your load calculation comes in at 165A and you've specified 200A service, the main disconnect must be rated 200A. Installing a 100A main breaker on a 200A service entrance conductor violates 230.79 and also creates a safety problem — the conductors are rated for more current than the breaker will trip at. The disconnect rating and the service conductor sizing must be consistent.
Does adding an EV charger require a service upgrade under CEC 230.79?
Not automatically, but often yes. Adding a Level 2 EV charger (typically 40A or 50A circuit) adds 9,600 VA at 100% continuous load to your Article 220 calculation. If your existing service has headroom — meaning the calculated load for the house without the EV charger is well under the current disconnect rating — you may not need an upgrade. But if you're already running a house with gas converted to electric appliances, the extra 40-50A often pushes the total above the current disconnect rating, triggering a 230.79 correction. Run the load calc before committing to a service size on the permit application.
What's the difference between the meter rating and the disconnect rating for CEC 230.79?
The utility meter is sized and installed by the utility company — it's not covered by CEC 230.79. What 230.79 cares about is the service disconnecting means, which is typically the main breaker in your panel or the main breaker in a meter-main combo unit. That breaker must be rated for the calculated load. The utility may install a 200A meter socket while you put in a 100A main breaker, but that 100A breaker still has to meet 230.79's requirement that it's rated for the load it serves. When the plans show a meter-main combo, label both the meter socket rating and the main breaker rating separately to avoid the correction.
My correction letter cites CEC 230.79 — do I need to hire an engineer?
Not necessarily. CEC 230.79 corrections are typically resolved by a licensed electrician or electrical contractor who can prepare the load calculation worksheet and redline the single-line diagram. In California, a C-10 Electrical Contractor can design and pull the permit for service work on residential projects without a licensed engineer. An engineer of record is usually only required if the project has a 400A or larger service, or if it's a commercial or multi-unit project. For a standard single-family or ADU correction, your electrical contractor should be able to prepare the revised load calc and resubmit directly.

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