Cost to Add a Subpanel in Marin

The main drivers are the feeder distance (the wire run from your main panel to the subpanel), the subpanel’s amperage, and the location and access for the work. A short run to an accessible indoor location is relatively inexpensive, while a long run to a detached garage or ADU — often requiring trenching or conduit and a heavier feeder — costs considerably more. The permit and inspection are part of the total, and your main panel must have spare capacity to feed the subpanel. An electrician assesses these factors to give you an accurate, itemized quote for your situation.

A subpanel makes sense when you need to power a group of circuits in one area — a garage, workshop, ADU, addition, or outbuilding — more efficiently than running each circuit individually back to the main panel. It centralizes the circuits locally, which is usually cheaper and cleaner for a larger set of loads at a distance. For just one or two circuits, a subpanel may be overkill; for a whole space with multiple circuits, it’s often the economical choice. Our subpanel decision guide covers when it fits versus other approaches in more detail.

The feeder is the run of wire (and often conduit) carrying power from your main panel to the subpanel, sized to the subpanel’s amperage. A longer run means more material — heavier wire over a greater distance — and more labor, especially if it must be trenched underground to a detached building, routed through finished walls, or navigate difficult terrain. Because the feeder scales with both distance and amperage, it’s typically the single largest variable in a subpanel’s cost. A subpanel a few feet from the main is far cheaper than one across the property.

Yes — a subpanel is fed from your main panel, so your main service must have enough spare capacity and a suitable spot to add the feeder breaker. If your main panel is already near its limit or full, you may need to address that first, which is a separate cost. This is why a subpanel project starts with checking your main panel’s capacity and available space. An electrician evaluates whether your main can feed the proposed subpanel, or whether a main panel upgrade is needed as well, before finalizing the plan and budget.

Yes. Adding a subpanel is significant electrical work that requires a permit and inspection to confirm it’s installed safely and to code — including proper feeder sizing, grounding, and connections. Permit and inspection costs are part of the budget, and the permitted, inspected work protects you at resale and with your insurer. A licensed contractor handles the permitting as part of the project. Given that a subpanel ties into your main electrical service and distributes power to a whole area, doing it permitted and inspected is essential rather than optional.

Adding a subpanel involves connecting to your main panel, sizing and running an appropriately rated feeder, proper grounding and bonding, and doing it all to code with a permit and inspection — which makes it a job for a licensed electrician, not a typical DIY project. Errors in feeder sizing, grounding, or connections create serious safety hazards. Because the subpanel draws from your main service and powers multiple circuits, correct professional installation is important for both safety and compliance. An electrician also confirms your main panel can support the subpanel before installing it, avoiding an unsafe overload.