A subpanel is a second, smaller breaker panel fed from your main panel. It is a great fix for running out of breaker spaces, or for bringing circuits out to a garage or shop. It is not a way to get more power.
What does a subpanel actually do?
A subpanel gets its power through one breaker in the main panel. Everything on the subpanel shares that feed, and the feed shares your home's total service capacity. So a subpanel gives you more breaker spaces in a convenient location, but the home can still only draw what the service (often 100 or 200 amps) allows.
When is a subpanel the right choice?
- Your main panel is in good shape but has no open spaces.
- You want circuits in a detached garage, shop, ADU or addition without running every circuit back to the house.
- A load calculation shows the service has room, you just need somewhere to land new circuits.
When do you need a new main panel or service upgrade instead?
- The main panel is a known problem brand, damaged, corroded or overheating. Adding a subpanel to it keeps the problem.
- The load calculation shows you are out of capacity (common with a 100-amp service plus an EV charger or heat pump). Then the fix is a service upgrade or, in some cases, a load-management device.
What does a detached garage or shop subpanel need?
A separate building fed by a subpanel generally needs its own disconnecting means and its own grounding electrode, with the neutral and ground kept separate at the subpanel, plus a feeder sized for the load and the distance. Trenching or conduit is often the biggest part of the job. Requirements vary by layout, so this is permitted work for a licensed electrician.
How much does a subpanel cost?
IES starting-at price for replacing a standard small subpanel, including the permit, is $1,250. A new subpanel, or one at a detached building, depends on distance, trenching and the feeder size, so we price it from photos or a site visit.
About these prices: rough starting-at prices from the IES price book. The final price depends on what we find on site, your utility and your city or county. Estimates are free.
Common questions
Does a subpanel give me more power?
No. A subpanel adds breaker spaces, but it is fed from the main panel and shares the same total service capacity. If you need more capacity, you need a service upgrade or a load-management solution.
Do I need a permit for a subpanel in California?
Yes, adding or replacing a subpanel is permitted electrical work in California cities and counties.
General information for California homes under the California Electrical Code (based on the NEC). Local rules and inspectors can vary. Not a substitute for an on-site inspection. Never work inside a panel, at the meter or on live circuits.