If your panel is full, or you are planning a garage, workshop or addition, the answer to “subpanel or main panel upgrade?” comes down to one distinction: a subpanel adds circuit space, and a main panel upgrade adds service capacity. A subpanel gives you more places to put breakers, but every amp it delivers still comes through your existing main service. A main panel upgrade, such as moving from 100 amps to 200 amps, raises the total amount of power your home can draw from the utility. Which one solves your problem depends on a load calculation, the step where a licensed electrician adds up what your home actually uses and what you plan to add.
This question comes up constantly in metro Atlanta. Many homes across Gwinnett and DeKalb were built in the 1970s, 1980s and 1990s with 100-amp or 150-amp service and panels sized for the appliances of that era. Today those same homes are adding EV chargers, home offices, heat pump water heaters, hot tubs and finished basements, all on top of the heavy summer air conditioning load that every Atlanta house carries from May through September. Some of those homes simply need more breaker spaces. Others are genuinely out of power. Getting the diagnosis right keeps you from paying for more than you need, or from adding circuits to a service that cannot support them.
What a Subpanel Actually Does
A subpanel is a secondary breaker panel fed from your main panel. A large breaker in the main panel, called the feeder breaker, supplies a set of wires, the feeder, that runs to the subpanel. Inside the subpanel, individual branch circuit breakers serve the outlets, lights and equipment in that area. It is a way to move a group of circuits closer to where they are needed, or to create room when every slot in the main panel is taken.
What a subpanel does not do is increase the amount of power your home can use. If your main service is 100 amps, adding a 60-amp subpanel does not give you 160 amps. It gives you a new branch of the same 100-amp tree. The feeder breaker limits how much the subpanel can draw, and the main breaker still limits the whole house.
That makes a subpanel the right tool in a few common situations: the main panel is physically full but the load calculation shows spare capacity; you are adding a garage, workshop or addition and want circuits located there rather than long runs back to the main panel; or a detached building needs its own panel with a local disconnect. The code requires specific protections for a subpanel, including properly sized feeder conductors, overcurrent protection at the main panel, and separated neutral and ground bars in the subpanel itself. Those details are why subpanel installation is a permitted job for a licensed electrician, not a weekend project, and why it is usually paired with new circuit wiring out to the garage, workshop or addition it serves. If you are wondering whether you can squeeze a few more circuits into your existing panel first, our article on whether you can add breakers to an electrical panel covers when that works and when it does not.
What a Main Panel Upgrade Changes
A main panel upgrade replaces the panel that receives power from the utility, and when capacity is the issue, it usually increases the size of the service itself. A move from 100 to 200 amps typically involves a new main panel, and often a new meter base, service entrance conductors and grounding, along with coordination with Georgia Power to disconnect and reconnect service. That coordination is why a service upgrade takes more scheduling than a subpanel, even when the physical work fits into a day or two.
A main panel replacement can also happen without a capacity increase. If the existing panel is an older model with a known safety history, such as Federal Pacific Stab-Lok or Zinsco, is corroded, or has damaged bus bars, replacing it at the same amperage improves safety and reliability. A homeowner who needs an electrical panel upgrade in Chamblee or anywhere else in the metro may be replacing an unsafe panel, adding capacity, or both, and the load calculation tells you which.
When a new main panel goes in, the local inspector will expect current code for the work being done, which can mean adding arc-fault (AFCI) or ground-fault (GFCI) protection on certain circuits and bringing grounding and bonding up to date. Those are good upgrades for an older home, and they are part of why the scope of a panel job varies. Sometimes the real problem is smaller: a single failing breaker, which circuit breaker replacement handles without touching the rest of the panel. Our guide to what is included in an electrical panel upgrade walks through the full scope in more detail.
The Load Calculation Decides
The load calculation is the fork in the road. Using the method in the National Electrical Code, Article 220, an electrician totals the home’s lighting and general-use circuits, the kitchen and laundry circuits, fixed appliances, the air conditioning or heat pump, the water heater and range, and then applies the demand factors the code allows. Then the electrician adds what you plan to install: an EV charger, a hot tub, a workshop’s tools, a second air conditioning system or an addition. The result shows whether your existing service can handle the new total.
If the calculation shows room to spare but you are simply out of breaker spaces, a subpanel is usually the efficient answer. If the calculation shows the new total exceeds what the service can support, a subpanel will not fix it. Adding circuits to an overloaded service leads to nuisance tripping at best and overheated equipment at worst. In that case, the service needs to grow, which means a main panel upgrade. Some homes need both: a service upgrade to add capacity and a subpanel to put circuits where they are needed, such as in a detached garage.
The National Fire Protection Association’s NFPA 70 page describes the National Electrical Code that Georgia jurisdictions adopt, including the load calculation and panel requirements local inspectors apply. Our article asking do I really need to upgrade my electrical service covers the everyday warning signs that point toward a capacity problem, such as lights dimming when the air conditioning starts or breakers tripping under normal use.
Common Scenarios and the Usual Answer
A full panel in a 200-amp home adding a few general circuits for a finished basement is a strong subpanel candidate, as long as the load calculation agrees. A 100-amp home adding a Level 2 EV charger and a hot tub is much more likely to need a service upgrade, since those two loads alone can take a large share of the available capacity. A detached workshop almost always gets its own subpanel with a local disconnect, fed from a main service that may or may not need an upgrade depending on the rest of the house. A home with an older panel brand known for safety problems should plan on replacing the main panel regardless of capacity.
Cost, Timeline and Permit Factors
Neither job has a single price, and anyone quoting a number before seeing your panel is guessing. The factors that move the cost are the distance between the main panel and the subpanel location, whether the feeder runs through an open basement or finished walls, whether a detached building needs trenching and outdoor-rated conduit, the size of the subpanel and the number of new circuits, the condition and amperage of your existing service, the utility coordination required for a service upgrade, and any code-required improvements triggered by the work.
Timelines vary the same way. An attached subpanel is often one to three days of work. A detached subpanel with trenching can take longer. A main service upgrade may be one to three days of physical work, but permit approval, utility scheduling and final inspection can stretch the overall project to a few weeks, and power is typically off for part of one day during the changeover.
Every version of this work requires a permit and inspection in Gwinnett County, DeKalb County, the City of Atlanta and surrounding jurisdictions. A licensed electrician pulls the permit, performs the work to code and meets the inspector. The same electrician can also handle related work in the same visit, such as replacing worn breakers in the main panel or wiring the new circuits the subpanel will serve. Homeowners planning panel upgrades in Suwanee and other north Gwinnett communities should also allow time for Georgia Power scheduling if the service size is changing.
Getting the Right Answer for Your Home
A subpanel and a main panel upgrade solve different problems. If you are out of space, a subpanel can add room for new circuits. If you are out of power, only a larger service fixes it. The load calculation is how you find out which problem you have, and it belongs at the start of any garage, workshop, addition or EV charger project, not after the circuits are already planned.
Panel work is never a DIY job. It involves the parts of your electrical system that carry the most current, it requires a permit, and in Georgia it must be performed by a licensed electrical contractor. The NFPA’s home fire safety resources are a good reminder of why proper panel and circuit protection matters, and why skipping the permit is never worth the risk. For the utility side of a service change, Georgia Power handles the disconnect and reconnect at the meter.
Kalahari Electrical Services is family-owned, licensed and insured (Georgia license EN213186), and has worked in homes across Lawrenceville, Gwinnett County and metro Atlanta since 2001. If you are out of breaker space or planning a project that adds new loads, call us at 678-665-2309 or reach us through our contact page to schedule an estimate that starts with a proper load calculation.
Frequently Asked Questions
Does a subpanel give my house more power?
No. A subpanel adds breaker space, but all of its power still comes through your main service and is limited by the feeder breaker in the main panel. If your home needs more total capacity, a main service upgrade is the fix.
How do I know whether I need a subpanel or a main panel upgrade?
A licensed electrician performs a load calculation that totals your current electrical demand and the loads you plan to add. If there is spare capacity and you are only out of slots, a subpanel usually works. If the new total exceeds your service, you need a main panel upgrade.
Do I need a permit to add a subpanel in Gwinnett County?
Yes. Adding a subpanel, adding circuits and upgrading a main panel all require an electrical permit and inspection in Gwinnett County and other metro Atlanta jurisdictions. A licensed electrician handles the permit as part of the job.
Can I add an EV charger without upgrading my main panel?
Sometimes. If the load calculation shows enough spare capacity, an EV charger can go on a new circuit in the existing panel or a subpanel. Homes with 100-amp service or several large loads often need a service upgrade first.