Why Understanding 200 Amp Breaker Compatibility Matters
A 200 amp breaker for sub panel installation is one of the most complex electrical upgrades homeowners face. The good news? You can feed a 200 amp sub-panel from a 200 amp main service – but only if your calculated load doesn’t exceed 200 amps total.
Key Compatibility Facts:
- Wire Size: 4/0 aluminum SER or 2/0 copper THHN minimum
- Load Calculation: Must follow NEC Article 220 requirements
- Grounding: Four-wire feeder with isolated neutral in sub-panel
- Installation: Requires permit and professional inspection
Many homeowners get confused by the numbers. Just because you have a 200 amp main panel doesn’t mean you can’t install a 200 amp sub-panel. The total calculated load is what matters, not the breaker ratings themselves.
Common scenarios where this makes sense:
- Large home additions with multiple circuits
- Detached workshops or garages
- EV charging stations requiring dedicated feeds
- Future-proofing for electrical upgrades
The real challenge isn’t the breaker size – it’s ensuring proper wire sizing, grounding, and code compliance. As one electrical forum user found: “I just bought an older house with a 200 A main panel and want to install a 200 A subpanel in the basement – is my plan code-compliant?” The answer depends on your specific load calculation and installation details.
I’m Dan Walsh, and I’ve spent years managing electrical technicians who handle complex panel upgrades including 200 amp breaker for sub panel installations throughout the Greater St. Louis area. Through AAA Home Services, I’ve seen how proper planning prevents costly mistakes and safety hazards.
When Does a Home Need a 200 Amp Sub-Panel?
Most homeowners only consider a 200 amp breaker for sub panel after breakers start tripping or the main panel runs out of spaces.
The modern home’s appetite for power keeps rising: central air, induction ranges, hot tubs, and dozens of always-charging devices all draw current. During our NEC Article 220 load calculations, we regularly see older 100 – 150 amp services operating near capacity.
Common triggers we see across St. Charles and O’Fallon homes:
- HVAC upgrades such as dual-stage heat pumps
- Level-2 EV charging (40-50 amp dedicated circuits)
- Large additions or basement finishes needing 10-20 new circuits
- Future-proofing for planned projects
Code compliance is not optional. Permits and professional inspections verify wire sizing, grounding, GFCI/AFCI protection, and working clearances. Our licensed electricians handle the paperwork and schedule inspections so you don’t have to.
Do You Really Need a 200 Amp Breaker for Sub Panel?
Bigger breakers don’t automatically give you more usable power; only the load calculation does. Thanks to diversity factors, the average residence rarely draws more than 100-150 amps at one time. Many projects are safely served by 60-100 amp sub-panels.
Reserve a true 200 amp feeder for:
- Whole-home remodels or large outbuildings
- Multiple EV chargers or heavy workshop machinery
- Homes where you know future expansion will happen soon
A right-sized solution costs less and is easier to install – that’s why our technicians always start with a detailed load calculation before recommending equipment.
For deeper details see our guide to Electrical Panel Upgrades.
Understanding the 200 Amp Breaker for Sub Panel
When you plan a 200 amp breaker for sub panel installation, a handful of technical points determine whether the project is safe and code-compliant.
Panel rating vs. breaker size
A 200 amp-rated panel is simply capable of carrying up to 200 amps; you can still feed it with a 100 amp or 150 amp breaker if the load calculation calls for that.
Feeder breaker vs. main breaker
The feeder breaker in your service panel protects the cable that runs to the sub-panel, while the sub-panel’s “main” is really a local disconnect. That local handle is mandatory in many jurisdictions whenever the sub-panel is in a detached building or located far from the service equipment.
Sub-feed lug kits
If your main panel lacks physical space for another large breaker, an approved sub-feed lug kit can tie directly to the bus bars without derating the service – a solution we often use in tight St. Louis basements.
Wire sizing in one glance
- 4/0 AWG aluminum SER
- 2/0 AWG copper THHN
Both satisfy NEC 310.12 for 200 amp residential feeders. Runs over 100 ft or through hot attic spaces may need upsizing for voltage drop or temperature derating.
Grounding & bonding essentials
- Always pull four conductors (two hots, isolated neutral, equipment ground).
- Keep the neutral bar floating; bond only the equipment grounding conductor to the enclosure.
- Detached structures need their own grounding electrode system under NEC 250.32.
These fundamentals – coupled with accurate torque on every lug – prevent the overheating that causes most panel failures we’re called to repair.
Code & Installation Checklist (No DIY Shortcuts!)
Installing a 200 amp breaker for sub panel is never a weekend project. Below is the streamlined checklist our electricians follow on every job from Wentzville to Chesterfield:
- Pull the electrical permit and submit the load calculation.
- Select a listed panel and breaker set compatible with your existing service equipment.
- Run a four-wire feeder sized per NEC 310.12 and Table 250.122.
- Mount the sub-panel with 30 in. of width, 36 in. of depth, and 6 ft 6 in. of headroom clearances.
- Keep neutral and ground isolated; install separate bars if needed.
- Land conductors to manufacturer torque specs (we use calibrated torque screwdrivers).
- Provide AFCI/GFCI protection where the code calls for it.
- Schedule rough-in and final inspections before energizing.
| Conductor Type | 200 Amp Size | Pros | Cons |
|---|---|---|---|
| Aluminum SER | 4/0 AWG | Affordable, flexible | Needs antioxidant paste |
| Copper THHN | 2/0 AWG | Higher ampacity, corrosion resistant | Higher material cost |
| Aluminum THHN | 4/0 AWG | Cost/ampacity sweet spot | Requires conduit & careful termination |
Skipping any step risks a red tag and, more importantly, your family’s safety. Our licensed team handles the process end-to-end so you don’t have to.
Budgeting, Parts & Planning Ahead
Panels and breakers are only part of the equation. Conductor cost (especially copper), trenching for detached garages, and inspection fees add up quickly. A typical timeline in St. Charles County looks like this:
- 1 – 2 weeks: permit approval and material procurement
- 1 day: feeder installation for a basement sub-panel
- 2 – 3 days: detached building with trenching and multiple inspections
Strategic placement of a single 200 amp sub-panel often saves money compared with running dozens of individual branch circuits from the main.
Avoid These 5 Common Mistakes
- Double-lugging service lugs instead of using a feeder breaker
- Bonding neutral and ground in the sub-panel
- Using an undersized grounding conductor
- Skipping the load calculation
- Ignoring manufacturer torque specs
We’re routinely called to fix the aftermath of these errors – like the overheated lug above – which usually costs more than doing it right the first time.
For more planning tips see Choosing the Right Electrical Wiring Installation Contractor.
Frequently Asked Questions about 200 Amp Sub-Panels
Can I feed a 200 Amp sub-panel from a 200 Amp main?
Yes—provided the NEC load calculation shows the combined demand does not exceed 200 amps. We normally install a dedicated 200 amp feeder breaker (or an approved sub-feed lug kit) with 4/0 Al SER cable.
How many sub-panels can one service supply?
There’s no numeric limit; the governing factor is still the load calculation. We’ve safely installed three or more sub-panels on a single 200 amp service when the diversified load allowed it.
Do I need a main breaker inside the sub-panel?
Not always, but a local disconnect is strongly recommended for panels located far from the service equipment or in detached buildings. A main-breaker sub-panel adds convenience and an extra layer of protection for only a modest cost difference.
Need a more specific answer? Our electricians can often provide same-day or next-day visits, schedule permitting.
Conclusion
Installing a 200 amp breaker for sub panel represents one of the most significant electrical upgrades you can make to your home. While the technical aspects might seem overwhelming, the reality is straightforward: yes, you can feed a 200 amp sub-panel from a 200 amp main service, but only when your total calculated load stays within safe limits.
Throughout this guide, we’ve covered the essential elements that make these installations successful. Load calculations drive everything – not the impressive-sounding breaker ratings. Your home’s actual electrical demand, calculated according to NEC Article 220, determines what’s safe and code-compliant.
The safety stakes couldn’t be higher. Proper grounding and bonding aren’t just code requirements – they’re what prevent electrical fires and protect your family. The four-wire feeder requirement, isolated neutral bars, and proper equipment grounding create multiple layers of protection that DIY installations often miss.
We’ve seen the consequences when homeowners try to tackle these projects themselves. Failed inspections, dangerous installations, and expensive corrections far exceed the cost of professional installation. One customer in St. Charles learned this the hard way when their DIY sub-panel installation failed inspection three times, ultimately costing more than twice what professional installation would have cost initially.
When does a 200 amp sub-panel make sense? Major home additions, EV charging installations, workshop upgrades, and consolidating multiple electrical projects all justify this investment. But remember – bigger isn’t always better. Many situations that seem to require 200 amps work perfectly with smaller capacity sub-panels.
The permit and inspection process exists for good reasons. These aren’t bureaucratic problems – they’re essential safety checkpoints that ensure your installation meets professional standards and protects your investment.
At AAA Home Services, our electrical technicians bring over 50 years of combined experience to every 200 amp breaker for sub panel installation. We serve homeowners throughout St. Charles, O’Fallon, Lake St. Louis, and the greater St. Louis area with the expertise that comes from handling thousands of electrical upgrades.
Our customers consistently choose us because we handle everything from initial load calculations to final inspections. We ensure your installation passes inspection the first time, meets all safety requirements, and provides the reliable electrical capacity your home needs.
Don’t risk your family’s safety with inexperienced contractors or DIY attempts. Electrical work involving service panels and high-amperage circuits requires professional expertise, proper tools, and thorough knowledge of electrical codes.
More info about Electrician Services
Whether you’re planning a major electrical upgrade or need immediate electrical service, our trained technicians can often provide same-day or next-day service depending on availability. We’re ready to help with the expertise and reliability you can trust for your most important electrical projects.
Contact AAA Home Services today to schedule a professional evaluation of your electrical upgrade needs. Let us show you why thousands of homeowners throughout the Greater St. Louis area trust us with their electrical projects.
