Decision guide
Do I Need a Panel Upgrade?
Not always. A load calculation decides it: an electrician totals what your home uses now and what you plan to add, using the method in the electrical code. If the result fits your current service, you may only need new circuits.
What a load calculation is
The National Electrical Code, which California adopts as its Electrical Code, sets out the method in Article 220. For an existing home, section 220.83 is the common route:
- Count general lighting and outlets at 3 volt-amperes per square foot, plus kitchen, laundry and fixed appliances at nameplate.
- Take the first 8,000 VA at 100% and the rest at 40%.
- When adding heating or cooling, add that equipment at 100%.
- Divide by 240 volts to get amps, and compare with your service.
Section 220.87 offers another path: use a year of your actual peak demand from utility meter data, which can show more room than the formula.
- Existing house loads
- Everything above the first 8 kVA, counted at 40% (includes the new range, EV charger and water heater)
- New heat pump, counted at 100%
The 80% rule, in one table
EV charging counts as a continuous load, so the circuit is sized at 125% of the charger's output (NEC 625.41). That is the "80% rule": a charger may use 80% of its circuit.
| Charger output | Circuit | Power at 240V |
|---|---|---|
| 32 amps | 40-amp circuit | 7.7 kW |
| 40 amps | 50-amp circuit | 9.6 kW |
| 48 amps | 60-amp circuit | 11.5 kW |
Many chargers can be set to a lower output, so a 32-amp setting can fit where a 48-amp one would not.
Alternatives PG&E promotes
PG&E's guide says "you may be able to electrify your home's appliances without a panel upgrade" and lists ways to do it:
- Circuit-sharing devices that pause one load, like an EV charger, while another runs.
- Smart panels and smart breakers that monitor use and limit loads.
- Lower-wattage appliances, such as 120-volt heat pump water heaters.
- Efficiency first: sealing air leaks and adding insulation shrink heating and cooling loads.
- Space-saving breakers where the panel is listed for them, when you're out of spaces rather than capacity.
Likely answers by situation
A starting point for the conversation with an electrician, not a substitute for the calculation.
| Your situation | Likely answer | Next step |
|---|---|---|
| One Level 2 charger, 200A service | Usually a new circuit only | Load calculation and permit |
| One Level 2 charger, 100A service | Depends; a lower charger setting or circuit sharing may avoid an upgrade | Load calculation |
| Heat pump replacing gas furnace and AC, 100A | Often fits on its own | Calculate the whole plan, not just the heat pump |
| Heat pump, induction range, water heater and EV, 100A | Often exceeds 100A | Plan a service upgrade with PG&E |
| ADU with its own kitchen and heating | Often a subpanel plus a larger service | Load calculation; PG&E if the service grows |
| Out of breaker spaces, capacity fine | Subpanel or space-saving breakers | No service upgrade needed |
| Federal Pacific or Zinsco panel | A replacement question, not capacity | Old panel replacement |
Signs your panel may be undersized
- The main breaker trips when several big loads run at once.
- There are no open spaces and the panel is full of tandem breakers.
- A home inspection noted double-tapped breakers or an overloaded panel.
- You're planning two or more new 240-volt loads.
A breaker that feels hot, a buzzing panel or a burning smell is different: call an electrician promptly rather than waiting to plan an upgrade.
When a service upgrade can't be avoided
If the calculation exceeds your service even with load management, the next step is a larger service, typically 200 amps. That brings in PG&E: a load assessment of up to 30 days, possibly design work and an advance, then reconnection after inspection.
Costs: panel upgrade cost guide. Incentives: rebates and tax credits.
Load and upgrade questions
What is the 80% rule for electrical panels?
It comes from how the code treats continuous loads, those running three hours or more, like EV charging. The breaker and wire must be rated for 125% of the continuous load, so the load can use only 80% of the circuit: a 48-amp charger needs a 60-amp circuit. It applies to circuits; whether the whole service is big enough is the load calculation's job.
Can I upgrade my panel without rewiring the house?
Usually, yes. A panel upgrade replaces the panel and service equipment, and existing branch circuits are reconnected to the new panel. The inspector may require current protection on circuits that are modified, and aluminum branch wiring is a separate question (see home rewiring).
Who can upgrade my panel?
A contractor with an active CSLB C-10 (Electrical) license, under a permit from your city or the County. PG&E handles anything on its side of the meter. See choosing an electrician.
Do I need a panel upgrade for a heat pump?
Not automatically. A heat pump replacing a gas furnace and AC adds load, but many homes fit it within their existing service. It gets tighter when you add an induction range, an EV charger and a heat pump water heater at the same time.
Do I need a panel upgrade for an EV charger?
On a 200A service, usually not; you need a dedicated circuit. On 100A, it depends on the calculation; a smaller charger or a circuit-sharing device can avoid the upgrade. See EV charger installation.
Sources
Next step
Get a load calculation
Tell us what you're adding. A local electrician can check your panel and service and tell you whether you need an upgrade at all.
Fill in the formOr call (925) 722-6103