Quick Summary for Pros
For a standard residential 200 amp service entrance, you're going to use 4/0 AWG aluminum or 2/0 AWG copper. This is allowed under the NEC's 83% rule for dwelling services. For any other 200 amp feeder (like to a subpanel in a detached shop), you must use a wire rated for the full 200 amps at 75°C, meaning you'll upsize to 250 kcmil aluminum or 3/0 copper. Always calculate for voltage drop on runs over 100 feet.
Who This Is For
- Residential Electricians: Professionals installing or upgrading main electrical services who need a quick reference on code-compliant wire sizes and best practices.
- General Contractors & Builders: Project managers who need to understand the requirements and cost implications of a 200 amp service for new construction or major remodels.
- Advanced DIYers & Homeowners: Individuals with significant electrical knowledge planning a major project (like a workshop subpanel) who need to understand the complexities before hiring a professional.
Who Should Avoid This
- Novice DIYers: If you're not deeply familiar with the National Electrical Code (NEC), conduit fill, and torque specifications, this guide is for planning purposes only. All service entrance work should be left to licensed professionals.
Understanding Ampacity and NEC Wire Sizing for a 200 Amp Service
When you're on the job, sizing wire for a 200 amp service isn't about guessing. It's about knowing the code and applying it to real-world conditions. The core concept is ampacity—the maximum current a conductor can handle before it starts to break down. This isn't a fixed number; it's determined by the wire material, its insulation, and the surrounding temperature. The National Electrical Code (NEC), specifically Table 310.16, is the rulebook we follow.
Why Terminal Temperature Ratings Are Non-Negotiable
Here’s a detail that trips up a lot of people. You might buy a 4/0 AWG aluminum wire with THHN insulation rated for 90°C. Looking at the NEC chart, you might think it's good for 205 amps. But in the field, you can almost never use that value. The circuit breakers and panel lugs where you terminate the wire are typically only rated for 75°C. The NEC demands you use the lowest temperature rating of any component in the circuit. So, that 90°C wire is instantly limited to its 75°C ampacity, which for 4/0 aluminum is only 180 amps.
This is a critical safety checkpoint. Overlooking this detail can lead to overheating at the terminals, creating a serious fire hazard and a guaranteed failed inspection. Always check the temperature rating on the panel and breaker, and size your wire based on the 75°C column in the NEC table.
How the NEC 83% Rule Applies to Residential Jobs
So if a 4/0 aluminum wire is only good for 180 amps at 75°C, how can we use it for a 200 amp residential service? This is where a specific code exception, NEC 310.12(A), becomes a contractor's best friend. For a dwelling's main service entrance conductors, the code allows you to size the wire for 83% of the service's rating. For a 200 amp service, that calculation is 200A x 0.83 = 166A. Your wire must have an ampacity of at least 166 amps.
This is precisely why 4/0 AWG aluminum (180A) and 2/0 AWG copper (175A) are the industry standards for residential 200 amp services. They both exceed that 166A minimum. However, it's crucial to remember this rule applies only to the main service conductors of a dwelling unit. If you're running a 200 amp feeder to a subpanel, this exception does not apply, and you must size for the full 200 amps. For smaller branch circuits, like those using 12 AWG copper wire, the sizing rules are completely different and much more straightforward.
Choosing Between Copper and Aluminum Conductors
On any 200 amp job, the first major decision is the conductor material. This isn't just about personal preference; it's a practical decision that impacts budget, labor, and long-term safety. For service entrance conductors, the choice between copper and aluminum is a classic trade-off between cost and workability. From my experience on countless job sites, the context of the installation dictates the right choice. Let's break down what matters in the real world.
Practical Comparison Table: Copper vs. Aluminum for a 200A Service
| Feature | Copper (3/0 AWG for Feeders, 2/0 for Service) | Aluminum (250 kcmil for Feeders, 4/0 for Service) |
|---|---|---|
| Material Cost | High (can be 2-3x the cost of aluminum) | Low (significant project cost savings) |
| Size & Workability | Smaller diameter, more flexible, easier to pull in tight spaces. | Larger and stiffer, requires more effort to bend and terminate. |
| Real-World Use Case | Best for feeders to subpanels, especially in conduit, and where space is a premium. | The undisputed standard for most residential service entrances due to cost. |
| Termination | More forgiving. Requires a clean, tight connection. | Critical. Requires anti-oxidant compound and precise torque settings to prevent failure. |
| Ideal User | Electricians working on high-end custom homes or complex commercial retrofits. | Production residential electricians and contractors focused on code-compliant, budget-conscious installations. |
The Bottom Line on Cost vs. Labor
There's no way around it: aluminum is dramatically cheaper. For a service entrance run, this can save hundreds of dollars in material cost alone, which is why it's the default for most residential builds. However, that cost savings comes with a trade-off in the field. Aluminum wire for a 200 amp service (4/0 AWG) is significantly thicker and stiffer than its copper equivalent (2/0 AWG). Wrestling that larger wire through conduit and into a packed panel takes more time and muscle.
In a tight remodel or a conduit run with multiple bends, the added flexibility of the smaller copper wire can actually save labor costs that offset its higher material price. On an open run for a new construction service drop, the extra work involved with aluminum is minimal, making it the clear economic choice. The decision comes down to balancing the upfront material savings of aluminum against the potential for easier installation with copper.
Termination: The Most Critical Step
This is where experience and attention to detail are paramount, especially with aluminum. Aluminum oxidizes instantly on contact with air, forming a resistive layer that can cause connections to overheat and fail over time. To combat this, every aluminum termination must be cleaned, coated with an anti-oxidant inhibitor, and tightened to the manufacturer's exact torque specification with a calibrated torque wrench. There is no room for "good enough." Copper is more forgiving and doesn't require an inhibitor, but a solid, torqued connection is still best practice for a reliable installation.
How to Handle Voltage Drop for Long Wire Runs
Voltage drop is the silent killer of performance in an electrical system. It's the gradual loss of electrical pressure as power travels down a wire. For short runs inside a house, it's rarely an issue. But when you're running a 200 amp feeder 150 or 200 feet out to a detached workshop or barn, it becomes a primary design concern. Ignoring it results in tools and motors that are starved for power, leading to poor performance, overheating, and a shortened lifespan. A pro knows to plan for this from the start to avoid a callback.
The NEC suggests a target of keeping voltage drop below 3% for a branch circuit or feeder. On a 240V system, 3% is a loss of over 7 volts. That's enough to cause visible dimming in lights and make a big difference to a welder or air compressor under load. To prevent this, you have to upsize your wire.
A Field-Tested Rule for Upsizing
While precise calculations are always best, a solid rule of thumb for the field is to upsize your wire one full gauge size for every 100-150 feet of distance. Let's apply this to a real-world scenario. You're installing a 200 amp subpanel in a workshop 150 feet away from the main house. A standard feeder for this load would be 3/0 copper or 250 kcmil aluminum.
Because of the 150-foot distance, the voltage drop on that standard wire would likely exceed the 3% target. Following our rule of thumb, you would need to upsize. The 250 kcmil aluminum would need to be increased to 300 or 350 kcmil, and the 3/0 copper would be bumped up to 4/0 copper. This larger wire has less internal resistance, ensuring that full power arrives at the workshop, even when heavy equipment kicks on. This is a critical step when setting up a powerful 200 amp sub panel at a distance.
As you can see, the further you go, the more the material choice and wire size matter. While aluminum saves money upfront, you may need a significantly larger and more cumbersome wire to combat voltage drop compared to a copper installation.
Service Entrance vs. Feeder: A Critical Distinction for Code Compliance
On the job, using the right terminology isn't about being picky; it's about making sure the right materials are used for the right application. Mixing up service entrance conductors and feeder conductors is a rookie mistake that can lead to a failed inspection and costly rework. Both can be rated for 200 amps, but the rules for sizing them are fundamentally different.
What Are Service Entrance Conductors?
Service entrance conductors are the main power lines for the entire building. They run from the utility's connection point (the "point of service") to the terminals of your main service disconnect, which is usually the main breaker in your primary electrical panel. These wires carry every amp that the building will use. For a residential property, this is where the special 83% sizing rule from the NEC applies, allowing us to use 4/0 aluminum or 2/0 copper for a 200 amp service. These conductors are typically installed as a bundled Type SE (Service Entrance) cable and connect directly to the 200 amp meter socket with a main breaker.
What Are Feeder Conductors?
A feeder is any set of conductors that runs between two overcurrent devices. In simpler terms, it's the wire that runs from a breaker in your main panel to a subpanel somewhere else—like a detached garage, a workshop, or a large addition. This is where the rules change. The 83% sizing allowance does NOT apply to feeders. A feeder must be sized to handle 100% of the load it serves, based on the 75°C ampacity tables.
This means if you are running a true 200 amp feeder to a subpanel, you cannot use the same 4/0 aluminum wire you used for the service. You must use a wire rated for a full 200 amps, which means upsizing to 250 kcmil aluminum or 3/0 copper. Mistaking this rule is one of the most common and expensive errors I see. It's a non-negotiable point for inspectors.
When to Hire a Licensed Electrical Contractor
I'm all for empowering people to tackle tough projects, but there are clear lines that shouldn't be crossed. Working on your home's 200 amp service is one of them. This isn't a gatekeeping statement; it's a critical safety warning backed by law in nearly every jurisdiction. Any work on the service entrance—the wires coming from the utility, the meter base, and the main panel—is the exclusive domain of licensed electricians.
The reason is simple: risk. A mistake here doesn't just trip a breaker; it can result in catastrophic arc flashes, house fires, or fatal electrocution. The available fault current from the utility can be thousands of amps, an amount of energy that requires specialized knowledge, tools, and personal protective equipment (PPE) to manage safely. A licensed professional carries the proper training and types of electrician insurance to handle this high-stakes environment.
The Unmistakable Signs You Need a Pro
There is no gray area on this. You must hire a licensed electrician for any job that involves:
- Upgrading your home's service from 100A or 150A to 200A.
- Replacing or relocating your main electrical panel.
- Replacing, moving, or working inside the electric meter base.
- Any task that requires the utility company to disconnect and reconnect power to your home.
If the job requires pulling the meter or cutting the utility tag, it's a job for a professional, full stop. They are the only ones authorized to coordinate with the power company and ensure the final installation is inspected and approved by the local authority, safeguarding your home and your insurance coverage.
Frequently Asked Questions About 200 Amp Wire
What size conduit do I need for 200 amp wire?
For the standard residential service entrance using 4/0 aluminum conductors, a 2.5-inch Schedule 40 PVC conduit is the most common choice. This provides enough space to pull the three main conductors and a ground without excessive friction or damage to the insulation. However, the final answer always depends on the specific wire type and number of conductors, as defined by the conduit fill tables in NEC Chapter 9. Always verify your specific combination against the code.
What size ground wire for a 200 amp service?
For a 200 amp service using 2/0 AWG copper main conductors, you need a #4 AWG copper grounding electrode conductor. If you're using 4/0 AWG aluminum mains, you'll need a #2 AWG copper ground wire. The ground wire size is determined by the size of your service entrance conductors, as specified in NEC Table 250.102(C)(1).
Can I use 3/0 aluminum wire for a 200 amp service?
No. 3/0 AWG aluminum wire has a 75°C ampacity of only 155 amps. This is below the 166-amp minimum required by the NEC's 83% rule for a residential 200 amp service. The minimum size for an aluminum service entrance conductor is 4/0 AWG, which is rated for 180 amps.
What is the difference between SER and SEU cable?
Both are types of Service Entrance (SE) cable, but they differ in their conductor count. SEU (Service Entrance, Unarmored) has three conductors: two insulated hot wires and a concentric neutral that wraps around them. It's primarily used for overhead service drops where the neutral can also serve as the ground. SER (Service Entrance, Round) has four conductors: two hots, an insulated neutral, and a bare ground wire, all bundled in a round jacket. SER is the standard choice for interior wiring from the main panel to large appliances or subpanels.
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