How to read your panel
Open the panel door. The large breaker at the top, or the one set apart from the rest, is the main. The number on its handle is your service size, usually 100, 150 or 200 amps.
- Count the open slots. A new 240-volt circuit needs two side by side.
- Look for half-width breakers. Lots of them means someone has already squeezed in more circuits than the panel was laid out for.
- Check the brand. Some older panels, Federal Pacific and Zinsco in particular, have well-known breaker problems. We recommend replacing those regardless of load.
What new equipment draws
A Level 2 EV charger typically runs on a 40 to 60 amp circuit. A heat pump’s outdoor unit needs its own dedicated circuit sized to the equipment. Neither runs at full draw all the time, which is why a load calculation looks at the whole house, not just the breaker sizes.
When 100 amps stops being enough
A 100-amp service can often take one major addition. It gets tight when a house adds two, such as an EV charger and a heat pump, or when it already has electric cooking, an electric dryer and central air. Some chargers can share capacity with the rest of the house and slow down when other loads are running, which can avoid an upgrade.
What an upgrade involves
- A load calculation and site visit
- A permit from your town
- Coordination with the utility to disconnect and reconnect service
- The panel swap, usually done in a day
- Town inspection before the job is closed out