Subpanel Installation: Cost, Process, and When You Need One
A subpanel installation typically costs $800 to $2,000, and is usually the more cost-effective choice when your main panel is out of physical breaker slots but has adequate total amperage — or when you need dedicated circuits for a detached garage, workshop, or ADU. Here's how to tell if a subpanel is the right fit for your situation instead of a full main panel upgrade.
⚡ Key Takeaways
- Subpanel installation typically costs $800–$2,000, usually less than a full main panel upgrade
- Best fit when you're out of physical breaker slots but total amperage capacity is fine
- Also the standard solution for powering a detached garage, workshop, or ADU
- A subpanel is fed from a dedicated breaker in your main panel, acting as its main disconnect
- Always requires an electrical permit — not a legal DIY project in virtually any US jurisdiction
What a Subpanel Actually Is
A subpanel is a secondary breaker panel fed by a dedicated circuit from your main panel, providing additional breaker slots and local circuit distribution without requiring a full main service upgrade. Think of it as an extension of your main panel's capacity, not a replacement for it — your main panel's overall amperage rating still governs your home's total available power.
Subpanel vs Full Main Panel Upgrade — Which One You Need
| Your Situation | Better Fit | Why |
|---|---|---|
| Out of physical breaker slots, amperage capacity is fine | Subpanel | Adds slots without touching your main service capacity |
| Total household amperage itself is insufficient | Main panel upgrade | A subpanel can't create capacity your main service doesn't have |
| Powering a detached garage, workshop, or ADU | Subpanel | Standard, code-compliant solution for this exact scenario |
| Panel is a documented risk brand (FPE, Zinsco) | Main panel replacement | A subpanel doesn't address the underlying safety issue |
⚠️ A subpanel cannot exceed the total amperage capacity of your main service. If your main panel and utility service are rated for 100A total, adding a subpanel doesn't create additional overall capacity — it only redistributes and adds breaker slots within your existing capacity, or requires your main service to already have adequate headroom.
What Subpanel Installation Actually Costs
| Scenario | Typical Cost | Notes |
|---|---|---|
| Small subpanel (60-100A), attached location | $800–$1,300 | Basement, garage attached to home |
| Larger subpanel (100-125A) | $1,200–$1,800 | More circuits, higher capacity |
| Detached structure (with trenching) | $1,500–$3,500+ | Distance and trenching significantly affect cost |
Check Your Main Panel's Available Capacity First
Confirm you have the headroom a subpanel needs before planning the project.
⚡ Run Free CalculatorSubpanels for Detached Garages, Workshops, and ADUs
Powering a detached structure is one of the most common reasons homeowners install a subpanel. This typically involves running underground or overhead feeder cable from the main panel to the new subpanel location, which is where trenching costs for underground runs become the biggest cost variable. Local code often requires the subpanel in a detached structure to have its own grounding electrode system and disconnecting means, separate from the main panel's grounding.
The Installation Process
- Load calculation to confirm your main panel has adequate capacity to feed the new subpanel
- Permit application with your local building department
- Running feeder cable from the main panel to the subpanel location
- Installing the subpanel with appropriate grounding and bonding
- Final inspection before the subpanel is approved for use
Permit Requirements
Subpanel installation requires an electrical permit in virtually every US jurisdiction, and given the connection to your main electrical service, this is not typically a legal DIY project the way some minor electrical work might be. A licensed electrician should handle both the permit and the installation.
Frequently Asked Questions
Q: Can I add a subpanel myself if I pull the permit?
A: Rules vary by state, but the connection work at the main panel specifically almost always requires a licensed electrician regardless of who pulls the permit. Confirm your specific jurisdiction's rules with your local building department before assuming any DIY scope.
Q: How far can a subpanel be from the main panel?
A: There's no fixed universal maximum distance, but longer runs require larger gauge feeder cable to avoid excessive voltage drop, which increases material cost. A licensed electrician calculates the correct wire size for your specific distance.
Q: Does a subpanel need its own AFCI/GFCI protection?
A: Circuits fed from a subpanel follow the same NEC requirements as circuits from a main panel — if a specific circuit type requires AFCI or GFCI protection, that requirement applies whether it originates from your main panel or a subpanel.
Q: How much does subpanel installation cost?
A: A subpanel installation typically costs $800 to $2,000 depending on amperage, distance from the main panel, and whether trenching is needed for a detached structure. This is usually cheaper than a full main panel replacement.
Q: When does a subpanel make more sense than upgrading my main panel?
A: A subpanel makes sense when your main panel lacks physical breaker slots but has adequate total amperage capacity, or when you need dedicated circuits for a detached structure like a garage, workshop, or ADU. A main panel upgrade is the better fit when your total household amperage itself is insufficient.
Q: Does a subpanel need its own main breaker?
A: A subpanel is fed from a breaker in the main panel that acts as its main disconnect, and depending on distance and local code, the subpanel itself may also require its own disconnecting means, particularly for detached structures.
Q: Do I need a permit for a subpanel installation?
A: Yes, in virtually all US jurisdictions, subpanel installation requires an electrical permit and is not typically a DIY-legal project given the connection to your main electrical service.