SUBpanel installation, replacement, and upgrades
Pure Home Electric installs, replaces, and upgrades subpanels for homeowners throughout the St. Louis metro area. Licensed and insured.*24/7 emergency service available.
subpanel services in st louis
Installation, Replacement
and Upgrades
Licensed, permitted, and done right the first time.
Your main electrical panel distributes power to everything in your home — but it can only do so much. When you finish a basement, wire a detached garage, add a workshop, or run a dedicated circuit for an EV charger on the far side of the house, running every new circuit all the way back to the main panel isn’t always practical. A subpanel solves that problem cleanly.
Pure Home Electric installs, replaces, and upgrades subpanels for homeowners throughout the St. Louis metro, including St. Louis City, St. Louis County, St. Charles County, and surrounding communities. Whether you need a new subpanel for a garage conversion, a replacement for an aging or failed unit, or an upgrade to handle a bigger load, we handle the entire job — design, permit, installation, and inspection.
Call Pure Home Electric today at (314)649-8687 to schedule service or get a free estimate. We are ready when you are.
St Louis SubPanel Services
Most Common
Subpanel Services
New subpanel installation. A subpanel installed where none existed before. Includes feeder sizing, feeder cable installation, subpanel mounting, breaker installation, and all required circuit wiring in the new location.
Subpanel replacement. An existing subpanel removed and replaced with a new unit. Common when the existing panel is overloaded, corroded, has insufficient circuit spaces, or is a brand with known reliability issues.
Subpanel upgrade. Increasing the amperage capacity of an existing subpanel to handle a larger load — most commonly when a workshop or garage is being converted to a more power-intensive use, or when EV charging is being added to a structure that already has a subpanel.
Detached garage and outbuilding wiring. Installing a subpanel in a detached garage or structure requires a disconnect switch, more materials, and trenching to run the wire underground from the main structure. Pure Home Electric handles the complete scope — trench coordination, conduit installation, feeder pull, panel installation, and all interior circuit work.
Basement finish electrical. A subpanel is often the most efficient way to supply power to a finished basement with multiple circuits for lighting, outlets, a home theater, a wet bar, or a bedroom. We design the subpanel location and feeder route as part of the overall basement electrical plan.
Workshop and home gym circuits. 240-volt circuits for table saws, compressors, welders, and other equipment, combined with general-purpose 20-amp circuits, require careful load planning. Pure Home Electric sizes the subpanel and feeder to handle what you need now with room for what you add later.
when is a subpanel needed
Common Uses Of
Subpanels
A subpanel – also called a secondary panel, satellite panel, or distribution panel – is a smaller circuit breaker panel that receives power from the main service panel and distributes it to a specific area of the home or a separate structure. It functions exactly like the main panel for the circuits it controls, with its own set of breakers that can be tripped and reset independently.
The main panel feeds the subpanel through a dedicated double-pole breaker and a four-wire feeder cable. That feeder breaker in the main panel is the subpanel’s overcurrent protection – which is why it must be sized correctly for the load the subpanel will carry.
A subpanel becomes necessary when you add a significant number of new circuits for a home addition, a workshop, a detached garage, or when the main panel is full. It is also the right solution when the location needing power is far enough from the main panel that running individual circuit cables the full distance would cost significantly more than installing a local distribution point.
The most common reasons St. Louis homeowners install subpanels:
- Running all the circuits for a basement finish from the main panel when the main panel is on the opposite end of the house.
- Wiring a detached garage or outbuilding that needs multiple circuits for lighting, outlets, a compressor, or EV charging.
- Adding a dedicated workshop or home gym that needs 240-volt equipment circuits plus general lighting and outlets.
- Installing a hot tub or pool equipment that requires dedicated 240-volt service and GFCI protection.
- Expanding an older home where the main panel is full and a panel upgrade isn’t the right solution.
- Adding an accessory dwelling unit that needs its own electrical distribution.
choosing a subpanel size
What Size Subpanel Does Your Home Need
Common subpanel sizes include 60-amp, 100-amp, and 125-amp panels. The right size depends on what you are powering and how much capacity you want for future expansion.
60-amp subpanel. Adequate for a small detached garage with basic lighting, a few outlets, and no large motor loads. Not appropriate if you plan to add EV charging, a compressor, or any 240-volt equipment.
100-amp subpanel. The most common choice for detached garages, finished basements, and workshops. Provides enough capacity for multiple 20-amp circuits plus one or two 240-volt circuits — EV charging, a compressor, a welder. Even if your calculation results in a small load, installing the absolute smallest subpanel is often impractical. Opting for a panel with extra spaces provides flexibility for future additions.
125-amp subpanel. Appropriate for larger workshops, garages with significant power tools, or accessory dwelling units that need to support a full range of kitchen and laundry circuits alongside living space circuits.
One important constraint: electricians advise that subpanels not exceed 50% of the main panel’s amps. A home with a 100-amp main panel cannot support a 100-amp subpanel — the main panel simply doesn’t have the available capacity. If your main panel is undersized for the subpanel you need, the right answer is a main panel upgrade first.
The feeder breaker in the main panel must match the subpanel’s amperage rating. For example, a 100-amp subpanel must be protected by a breaker no larger than 100 amps. For a 100-amp copper feeder, the NEC specifies #3 AWG THWN/THHN copper conductors per NEC Table 310.16.
Pure Home Electric performs a load calculation before recommending a subpanel size. We do not default to the smallest or cheapest option — we size for what your project needs with room for what comes next.
FAQs
Frequently Asked
Questions
What is the difference between a subpanel and a main panel?
The main panel connects directly to the utility service entrance and is the primary distribution point for all electrical circuits in the home. A subpanel is a secondary panel fed by the main panel through a dedicated feeder circuit. The subpanel distributes power to a specific area — a garage, a basement, a workshop — while the main panel continues to serve the rest of the home. A subpanel does not have its own utility connection and cannot function independently of the main panel.
Can I add a subpanel to a 100-amp main panel?
Yes, but with an important limitation. Electricians advise that subpanels not exceed 50% of the main panel’s amperage. On a 100-amp main panel, that means a subpanel of no more than 50 to 60 amps — enough for basic garage lighting and outlets, but not enough for EV charging or significant equipment loads. If you need a larger subpanel and have a 100-amp main panel, a main panel upgrade to 200 amps is typically the right first step. Pure Home Electric will evaluate your main panel capacity before recommending a subpanel size.
Does a subpanel need its own main breaker?
Not always. Most subpanels installed inside the same building as the main panel are main-lug panels — they rely on the feeder breaker in the main panel as their overcurrent protection and do not need a separate main disconnect. Subpanels installed in detached structures are a different matter. Installing a subpanel in a detached garage or structure requires a disconnect switch at or near the structure, per NEC requirements, so the structure’s electrical system can be isolated without going back to the main panel. Pure Home Electric builds the correct disconnect configuration into every detached structure job.
Will I need a permit for a subpanel in St. Louis?
Yes. St. Louis City and St. Louis County require permits for electrical subpanel work, with active inspections following installation. Permit requirements apply throughout St. Charles County and surrounding municipalities as well, though the specific process and fees vary by jurisdiction. Pure Home Electric handles the permit application and coordinates the inspection as part of every subpanel job — you do not need to manage that process separately.
Can a subpanel increase my home's electrical capacity?
A subpanel does not increase the total amperage coming into your home — that is determined by your main panel and the utility service. What a subpanel does is extend your existing capacity to a new location and organize circuits more efficiently. If you need more total capacity — for example, to support an EV charger, a large workshop, and a full household load simultaneously — that requires a main panel upgrade. A subpanel can then distribute that upgraded capacity where you need it.
How long does a subpanel installation take?
A straightforward interior subpanel installation — adjacent to the main panel or in a basement mechanical room with a short feeder run — is typically completed in a single day. Detached garage jobs that require underground conduit and trenching take longer, usually two to three days depending on trench distance and whether the trench work is coordinated with a separate contractor. Pure Home Electric gives you a clear timeline estimate as part of the project scope before work begins.
Does Pure Home Electric handle the full scope — panel, feeder, trench, and circuits?
Yes. For detached garage and outbuilding subpanel jobs, Pure Home Electric manages the complete electrical scope: feeder sizing and installation, underground conduit and pull, disconnect switch installation, subpanel mounting and wiring, and all interior circuit work inside the structure. Trench excavation is coordinated as part of the project. You work with one contractor and get one estimate that covers the full job.
What Does Subpanel Installation Cost in St. Louis?
The average cost to install a subpanel is $400 to $600 for 50 amps or $500 to $1,500 for 100 amps, including labor and materials. For subpanels generally, the average installed cost runs $1,500 to $2,500 when factoring in more complex installations with longer feeder runs or detached structure wiring.
The basic cost to install an electrical subpanel in the St. Louis area runs $924 to $1,119 per subpanel as of 2026, with the final number moving based on these variables:
Feeder distance. The longer the run from the main panel to the subpanel location, the more wire and conduit the job requires. A subpanel installed in an adjacent basement mechanical room costs considerably less to feed than one installed in a detached garage 80 feet away.
Underground versus interior runs. Detached garages and outbuildings require underground conduit from the main structure. Trenching costs $6 to $13.50 per foot to bury electrical wiring, which adds to the total on any detached structure job.
Panel size and circuit count. A larger panel with more circuit spaces costs more than a smaller unit. The number of circuits you want wired at installation also affects labor.
Main panel capacity. If the main panel does not have a suitable open breaker slot or sufficient remaining capacity for the subpanel feeder, work at the main panel is required before the subpanel can be installed.
Permit and inspection fees. Electrical permits cost $50 to $350 and an electrical inspection costs $100 to $250. These vary by municipality across the St. Louis metro. Pure Home Electric handles the permit application and coordinates the inspection as part of every job.
Pure Home Electric provides written estimates before any work begins. There are no surprise charges at the end of the job.
