The short version
- The number on your main breaker, often 100, 125, 150 or 200 amps, is your panel's capacity.
- Electricians use a code-based load calculation to decide if new equipment fits, and it often shows more room than people expect.
- Load management, 120V appliances and right-sized equipment can often avoid a costly service upgrade.
- A few older panel brands are commonly recommended for replacement regardless of capacity.
What your panel does
Your electrical panel takes power from PG&E and divides it into circuits for your home. Its capacity, in amps, is usually printed on the main breaker at the top. Older homes often have 100-amp panels, while newer homes typically have 200 amps.
Capacity is only part of the story. A panel also needs open spaces for new breakers, and it needs to be in good condition.
How an electrician decides if it fits
Adding up the numbers on your breakers badly overstates your real load, because everything never runs at once. For existing homes, electricians use a load calculation from the National Electrical Code that counts lighting, appliances and new equipment, then discounts for the fact that loads don't all peak together. The result is compared with your panel's rating.
An electrician may also use 12 months of your smart meter data to see your actual peak demand, which often shows even more room. The Panel Readiness Check walks through a simplified version of the code calculation.
Ways to avoid an upgrade
- EV load management: smart chargers or energy management systems slow charging when the home is busy.
- 120V heat pump water heaters: plug into a standard outlet instead of needing a new 240V circuit.
- Heat pumps without backup heat strips: often unnecessary in the North Bay, and they add a lot of load.
- Smart panels and circuit-sharing devices: let two large loads share one circuit or manage power automatically.
- Right-sized equipment: a correctly sized heat pump or charger uses less capacity than an oversized one.
When an upgrade does make sense
Sometimes an upgrade is the right call: when the panel is too small for your plans even with load management, when there's no room for breakers, or when the panel is old or damaged. Upgrading the service usually involves PG&E as well as your electrician, so allow extra time for scheduling. Some panels, including Zinsco and Federal Pacific, have known problems and are commonly replaced before adding major loads.
Panels and solar
Solar and batteries connect to your panel too. A common code rule, the "120% rule," limits how large a solar breaker a panel can accept. When a system is larger, installers often use a main breaker derate or a connection ahead of the main breaker. Both are routine; just ask which approach your installer is planning.
Questions to ask your contractor
- Will you do a load calculation, and can I see it?
- Could load management or a 120V appliance avoid an upgrade?
- Do I have enough open breaker spaces?If not, ask about tandem breakers or a subpanel.
- Is my panel in good condition, and is the brand a concern?
- If I need an upgrade, how long will PG&E coordination take?
Common mistakes to avoid
- Assuming every upgrade needs a new panel. Many don't.
- Adding up breaker sizes. That overstates your real load.
- Planning one upgrade at a time. Plan the EV, heat pump and solar together.
- Ignoring an old panel brand. Some are best replaced first.
Run the numbers for your home
This guide is general education, not advice for your specific home. Equipment, rebates and PG&E rates change; confirm details with a qualified professional. Unfamiliar term? See the glossary. Have a question it didn't answer? Ask Robert.