Subpanel installation cost typically runs $400 to $600 for a 50-amp subpanel and $500 to $1,500 for a 100-amp subpanel, with the final number depending on amperage, distance from the main panel, and how much drywall or wall repair the job requires. For homeowners adding a garage workshop, a detached ADU, or extra capacity for a growing list of appliances, a subpanel is often the more affordable answer compared to a full panel upgrade – but only if your main panel actually has the spare capacity to support it.
This guide walks through what a subpanel actually does, how its cost compares to a full panel upgrade, and the warning signs that tell you which one your home really needs. It’s a question worth getting right the first time, since choosing the wrong option can mean paying for a subpanel that never had enough upstream capacity to work properly, or paying for a full panel upgrade you didn’t actually need.
What a Subpanel Actually Does
A subpanel is a secondary distribution point that extends circuits from your main panel to a specific area of the home – a garage, a detached structure, a finished basement, or an addition. Importantly, a subpanel does not increase your home’s total electrical capacity, it only redistributes power that’s already available at the main panel to a more convenient location.
That distinction trips up a lot of homeowners. If your main panel is already near its rated capacity, adding a subpanel doesn’t create more power out of thin air – it just moves existing capacity somewhere more useful. If your main panel doesn’t have enough spare capacity to feed a new subpanel in the first place, a panel upgrade has to happen first.
Subpanel Cost by Amperage
Amperage is the biggest factor in the equipment cost, though labor typically makes up the larger share of the total bill. A 100-amp subpanel unit alone typically runs $100 to $200, a 150-amp unit $150 to $250, and a 200-amp unit $250 to $350 before labor, permits, or wiring are factored in. Most residential garage or ADU subpanels fall in the 50 to 100-amp range, which covers lighting, outlets, and moderate appliance loads comfortably.
Labor generally takes 4 to 8 hours for a straightforward installation, though that stretches considerably if the subpanel needs to be located far from the main panel or if significant wall or ceiling repair is involved after running new circuits.
Subpanel vs. Full Panel Upgrade
This is the question we get asked more than almost any other: should you install a subpanel, or upgrade your main panel instead? A subpanel costs less upfront, typically $2,000 to $3,000 installed, but only makes sense if your main service already has adequate spare capacity and the new load is concentrated in one area of the home. A main panel upgrade costs more but increases your home’s total electrical capacity and lets you redistribute power throughout the entire house, not just one area.
A good rule of thumb: if you’re adding a workshop, a detached garage, or a single new high-draw circuit in one part of the home, a subpanel is usually the right call. If your whole panel is aging, undersized, or already at capacity with no room for a new feed breaker, a full panel upgrade is the more honest recommendation, even though it costs more upfront.
Cost Factors Beyond Amperage
Amperage sets the baseline, but several other factors move the final number up or down. Distance between the main panel and the subpanel’s location is usually the biggest one – every additional foot of wire and conduit adds material and labor cost, and a subpanel installed on the opposite side of the house or in a detached structure costs meaningfully more than one installed a few feet away on the same wall.
Wall and ceiling repair after the wiring is run is another factor homeowners sometimes forget to budget for. If the run passes through finished drywall, your electrician either has to cut and patch access points or fish the wire through existing cavities, and patching, texture-matching, and repainting afterward is typically a separate cost from the electrical work itself.
Permit fees vary by city but are a required part of every legitimate quote. If a quote you’re comparing doesn’t mention a permit fee at all, that’s worth asking about directly – it may mean the fee is bundled in, or it may mean the electrician is planning to skip it, which is a real problem if you ever need to sell the home or file an insurance claim involving that circuit.
Signs You Might Need a Subpanel
- You’re finishing a garage, workshop, or detached structure and need dedicated circuits there
- You’re adding a home addition and don’t want to run every new circuit all the way back to the main panel
- You want a dedicated EV charging circuit in a garage that’s a long distance from your main panel
- Your main panel has spare capacity but not enough open breaker slots for the new circuits you need
Frequent breaker trips, heat, or buzzing coming from the main panel are also worth having evaluated, though those symptoms sometimes point toward a panel problem rather than a capacity problem – which is exactly why a licensed electrician’s assessment matters more than guessing from a blog post.
Signs You Need a Panel Upgrade Instead
A panel older than 25 years, or one that’s already at capacity for your home’s current needs, is a common trigger for a full upgrade rather than a subpanel. Homes built in the 1980s and 1990s in particular often weren’t designed around today’s electrical demands – central air, multiple large-screen TVs, home office equipment, and EV charging all draw more power than a typical panel from that era was sized for.
If you have a Zinsco or Federal Pacific panel, replacement is a safety priority regardless of capacity questions – both brands carry known fire-risk histories and most licensed electricians recommend replacing them outright rather than adding a subpanel downstream of either one.
“A lot of homeowners come to us already decided on a subpanel because it’s the cheaper option, and sometimes that’s exactly right. But if I open the main panel and it’s already maxed out, I’m not going to recommend a subpanel just because it’s what was asked for – I’ll tell you honestly if the panel itself needs the upgrade first.”
– Razmik, Electrical Land
Planning for EV Chargers and Future Loads
A dedicated subpanel is a popular choice for homeowners planning EV charging in a garage that sits far from the main panel, since it avoids running one long, expensive circuit and instead creates a local distribution point that can support the charger plus future additions like garage lighting or a workshop outlet circuit. If a second EV is a real possibility down the road, it’s worth sizing the subpanel with that in mind from the start rather than adding a second one later.
Detached workshops and garages are one of the most common subpanel use cases we see across Orange County, since running individual circuits from the main house panel to a detached structure gets expensive fast once trenching or conduit runs are involved. Sizing the subpanel a little larger than your immediate needs is usually a small incremental cost during the original installation, compared to the cost of adding a second subpanel or resizing the first one a few years later once you’ve added more appliances than originally planned.
Permits and Code Compliance
Subpanel installations require an electrical permit in every jurisdiction we serve, and for good reason – improper subpanel wiring, particularly around neutral and ground bonding, is a common source of dangerous mistakes in DIY and unlicensed installations. A subpanel’s neutral and ground bars must be kept separate from each other, unlike the main panel where they’re bonded together, and getting this wrong creates a genuine shock hazard.
Your electrician will also verify your main panel’s total demand using National Electrical Code load calculations before adding a subpanel, to confirm the new circuit won’t overload the service as a whole. This step is easy to skip when a homeowner is in a hurry to get a garage or workshop powered up, but it’s the difference between a subpanel that performs reliably for decades and one that trips or overheats the first time several circuits run at once.
If your subpanel will be installed in a detached structure rather than the same building as the main panel, code also requires a main breaker at the subpanel itself, functioning as a disconnect for that structure. A subpanel installed in the same building as the main service panel typically doesn’t need its own main breaker, since the main panel’s breaker already serves that purpose – one more detail that’s easy for an inexperienced installer to get wrong.
What to Expect During Installation
A typical subpanel installation starts with your electrician shutting off power to the main panel, confirming the existing load with a load calculation, and running a feeder circuit – wire and conduit sized to the subpanel’s amperage – from the main panel to the new subpanel location. Once the subpanel is mounted and the feeder is connected, your electrician adds the individual circuit breakers for whatever the subpanel is feeding, whether that’s garage outlets, workshop equipment, or an EV charging circuit.
Most straightforward installations wrap up in a single day, with the final step being a call for city inspection before the subpanel goes into regular use. Complex installations involving trenching to a detached structure or significant wall repair can stretch across two or more days, particularly if permitting requires an inspection between the rough-in and cover stages.
Expect a brief power outage to the main panel while the connection is made – your electrician will schedule this at a convenient time and can usually keep it under an hour for a standard residential installation.
Common Subpanel Locations We See
Garages are by far the most common subpanel location, typically feeding a mix of general outlets, workshop tool circuits, garage door opener power, and increasingly an EV charging circuit. Detached structures – pool houses, workshops, converted sheds, and ADUs – are the second most common category, since running individual circuits across a yard for each new device quickly becomes more expensive than a single subpanel feeder.
Finished basements and additions round out the most frequent scenarios, particularly in homes where the original panel simply wasn’t sized with a future addition in mind. In each of these cases, the core question is the same: does the main panel have enough spare capacity to feed a new subpanel, and is the distance short enough to keep the job cost-effective compared to other options.
Getting an Accurate Quote
Because subpanel installation cost depends so heavily on distance, amperage, and what’s already available at your main panel, the only way to get a number you can trust is an in-person evaluation. An electrician needs to see your main panel’s current load, confirm available capacity, and measure the run to your subpanel’s planned location before pricing the job accurately. A phone quote based on square footage alone simply can’t account for any of that, so treat any number you get without a walk-through as a rough starting point rather than a firm figure.
If you’re weighing a subpanel installation for a garage, workshop, or addition in Westminster or anywhere in Orange County, our team can evaluate your main panel’s capacity and give you a real recommendation – subpanel or full upgrade – based on what we actually find. We also handle EV charger installation if your subpanel project is charger-driven, and coordinate with the Westminster plumbing team on combined garage and ADU projects. Reach out to our Westminster, CA office to schedule an evaluation.
