Does your Sunnyvale house need a 200 A panel?

The short answer: if you plan to add any two of an EV charger, a heat pump, an induction range or a battery, a 100 A panel will not pass the load calculation. One of them, probably. Two, almost never.

How the calculation works

NEC 220.83 adds up the house: three watts per square foot for general lighting and receptacles, the kitchen and laundry circuits, the fixed appliances, then the largest of heating or cooling. It applies a demand factor, because not everything runs at once, and gives you amps. An EV charger counts in full, as a continuous load. That is what tips most Sunnyvale homes over.

Signs you are already close

• Lights dim when the dryer or the AC starts.
• Tandem (double) breakers in half the spaces.
• A sub-panel in the garage fed from the main, feeding another in the laundry.
• The panel is a Zinsco or Federal Pacific Stab-Lok. These are a replacement on their own.

What an upgrade is

A new 200 A meter-main, new grounding, every circuit re-landed, one scheduled outage of about six hours while PG&E pulls and resets the meter. Two to three weeks from the site walk, most of it waiting on the permit and the utility appointment.

What it is not

It is not a rewire. Your circuits stay; they land in a new panel. And it is not always needed: a 125 A panel with a load-managed charger is often the better answer. See Lakewood.