Subpanel Installation
You need power somewhere your main panel can't easily reach. A detached garage, a workshop, an addition, an Accessory Dwelling Unit (ADU). Or your main panel is physically full and there's no room to add circuits for what you're building. A subpanel solves both problems by creating a second distribution point fed from the main panel.
There's one thing a subpanel doesn't do: it doesn't give your home more total power. It distributes what you already have to a new location. If your home needs more capacity than the existing service provides, that's a service change, not a subpanel. We figure out which one applies during the on-site evaluation.
This page describes the general scope of a subpanel installation. Every project is different. We evaluate your main panel, your existing service capacity, the location of the new subpanel, and local code requirements on-site before providing an estimate.
What a Subpanel Does
Your main panel divides the home's electricity into circuits. Each circuit has a breaker. A subpanel does the same thing, but in a second location. It connects back to the main panel through a dedicated feeder circuit, drawing from the home's existing electrical capacity.
A subpanel is the right solution when you need circuits in a location that's too far from the main panel to run individual wires, or when the main panel has no physical room for additional breakers. It organizes the new circuits in one place, close to where the power is being used.
What it doesn't change is how much total power the home receives from the utility. The main service rating stays the same. A subpanel shares capacity with the main panel. If the combined demand of the house and the subpanel exceeds what the service can deliver, the main breaker trips.
When You Need One
Basement finishes and home additions
Finishing a basement is one of the most common reasons for a subpanel. A finished basement typically adds a bathroom, a bedroom, a living area, and sometimes a kitchenette or wet bar. Each of those spaces needs dedicated circuits: lighting, outlets, GFCI-protected receptacles in the bathroom, AFCI protection in the bedroom and living areas. That's six to ten new circuits that the main panel often doesn't have room for.
A subpanel in the basement puts the distribution close to where the power is being used, keeps the wiring runs short, and organizes everything in one place. It's cleaner than running ten individual wires back to a main panel on the other side of the house, and easier to troubleshoot later. Home additions work the same way: when you're adding enough new circuits that the main panel can't accommodate them, a local subpanel is the right approach.
Detached garages and workshops
Equipment like welders, air compressors, car lifts, and EV chargers runs on 240 volts and draws heavy current. A detached garage needs its own panel to distribute those circuits locally and provide a disconnect at the building. Running individual circuits from the main panel across the yard isn't practical or code-compliant for most setups.
Accessory Dwelling Units
An ADU operates as an independent living space with its own heating, cooling, kitchen appliances, and lighting. That electrical demand requires a dedicated subpanel sized for the full range of equipment in the unit. In jurisdictions that have adopted Colorado's Electric Ready code, an ADU subpanel must also accommodate pre-wiring for future electric appliances and EV charging, even if gas appliances are installed initially. We confirm what your jurisdiction requires during the evaluation.
Outbuildings
Barns, sheds, pool houses, and detached studios on larger properties in communities like Evergreen, Conifer, and Morrison need their own electrical distribution. The distance from the main panel to an outbuilding introduces wiring challenges (the farther the run, the heavier the wire needed to maintain proper voltage), and code requires a separate disconnect and grounding system at any detached structure with its own subpanel.
The main panel is full
If your main panel has no empty breaker slots but your home's total electrical demand still fits within your service rating, a subpanel adds the physical space for new circuits without upgrading the service. This is a common situation in older homes that have accumulated circuits over decades.
When a Subpanel Won't Solve the Problem
A subpanel creates more room for circuits. It does not increase how much electricity your home receives from the utility.
If your main panel is full and your home is already running close to its service capacity, adding a subpanel with more equipment on it will push the total demand past what the service can handle. The main breaker will trip. In that situation, the home needs a service change to increase the overall capacity before a subpanel can be added.
This is the most common point of confusion with subpanel projects. We determine whether a subpanel alone will work, or whether a service upgrade is needed first, during the on-site evaluation. It's based on a calculation of the home's total electrical demand against the existing service rating.
Detached Structures: What's Involved
When the subpanel is going in a detached building, the project includes work between the two structures.
Underground conduit and wiring
A feeder circuit runs from the main panel to the new subpanel through buried conduit. Along the Front Range, conduit is buried at or below the frost line (36 inches in the Denver metro and foothills) to prevent damage from the freeze-thaw cycle. The distance between the main panel and the detached structure determines the wire size needed to maintain proper voltage at the far end. Longer distances require heavier wire.
Trenching
The conduit path has to be excavated. This disrupts landscaping, and depending on the route, may require cutting through driveways, patios, or other hardscaping. The trench stays open until the electrical inspector signs off on the installation.
Grounding at the outbuilding
The National Electrical Code (NEC) requires any detached structure with a subpanel to have its own grounding electrode system: ground rods driven into the earth at the outbuilding and bonded to the subpanel. This provides a local path to ground for fault current and lightning, rather than relying on the long wire run back to the main house.
In communities with architectural review requirements (Highlands Ranch, Genesee, Ken Caryl, and others), exterior electrical work on detached structures may need approval before installation begins. We identify whether this applies during the evaluation.
Colorado Electric Ready Requirements
In jurisdictions that have adopted Colorado's Electric Ready code (HB 22-1362), subpanels for certain structures trigger additional requirements beyond a standard installation.
Detached garages. Any new parking structure requires a dedicated 240-volt, 40-amp circuit for future EV charging, terminated and labeled at the subpanel, regardless of whether the homeowner currently owns an electric vehicle. The subpanel must be sized to accommodate this circuit.
ADUs. A subpanel for an ADU must be sized for all-electric appliance loads. If the ADU includes parking, the EV-ready circuit applies. If the roof meets the minimum area requirements, solar-ready conduit and reserved panel space for a future solar breaker are also required.
These requirements apply in adopted jurisdictions. Not every municipality in our service area has adopted the Electric Ready code on the same timeline. We confirm which requirements apply to your project and location during the evaluation.
The Process
On-site evaluation
We look at the main panel, the existing service capacity, the location for the new subpanel, and the route for the feeder circuit. If the subpanel is going in a detached structure, we assess the trenching path, distance, and soil conditions. No estimate gets written without seeing the full picture.
Permit
Subpanel installations require a permit in every Colorado jurisdiction. We pull the permit and handle the paperwork. The permit fee and the time to file and coordinate everything is part of the project.
Installation
For interior subpanels (basement finish, addition), the work is contained to the main panel area and the new location. For detached structures, the project includes trenching, conduit, wiring, and grounding at the outbuilding. Power at the main panel is off for a portion of the work while the new feeder breaker is tied in.
Inspection
The city or county inspector reviews the installation. For detached structures, the trench and conduit are inspected before backfill. The inspector checks the subpanel wiring, the neutral and ground separation, and the grounding system.
Documentation
You get a passed inspection on file and a panel directory for the new subpanel. We provide a 1-year parts warranty from the date of final inspection and a lifetime workmanship warranty.
Frequently Asked Questions
Does a subpanel give my home more power?
No. A subpanel distributes your existing electrical capacity to a new location. It creates more room for circuits, but it doesn't increase the total power your home receives from the utility. If the home needs more capacity, that's a service change.
What size subpanel do I need for a detached garage?
It depends on what equipment you're running. A garage with basic lighting and outlets needs less than one with a welder, an air compressor, and an EV charger. We size the subpanel based on the actual and anticipated loads during the evaluation.
Will my yard be dug up for a subpanel installation?
For detached structures, yes. A trench is dug between the main panel location and the outbuilding for underground conduit. The depth, route, and extent of the excavation depend on the distance and what's in the way. The trench stays open until the inspector signs off.
Does a subpanel installation require a permit?
Yes. In every Colorado jurisdiction. The permit ensures the work is inspected before it's covered up and energized. Unpermitted subpanels can void insurance coverage and create problems when selling the home.
What if my main panel doesn't have room for the subpanel breaker?
This is one of the most common situations. When the main panel is full, an existing two-pole breaker (often a dryer or oven circuit) can be relocated to the new subpanel, freeing up space in the main panel for the subpanel feeder breaker. We assess the options during the evaluation.
Do ADU subpanels have additional code requirements in Colorado?
In jurisdictions that have adopted Colorado's Electric Ready code, yes. ADU subpanels must be sized for all-electric loads, include a dedicated EV-ready circuit if parking is provided, and may require solar-ready provisions. We confirm which requirements apply to your jurisdiction and project.
Who does the work at Dunlap Electric?
The same person who evaluates your panel and writes the estimate. We don't hand jobs off to a crew or a subcontractor. One master electrician, start to finish.
This page describes general project scope and is not a quote, diagnosis, or commitment. References to the National Electrical Code (NEC) are based on the 2023 NEC as adopted by Colorado at the time of writing and are for context only. They do not replace the currently adopted code in your jurisdiction. Your local Authority Having Jurisdiction (AHJ) and electrical inspector determine what applies to your project. The specific scope and requirements for your home can only be determined by a licensed electrician during an on-site evaluation. Jesse Dunlap is a Colorado Licensed Master Electrician, in the trade since 1998.
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