For a standard residential 200-amp service, 2/0 AWG copper or 4/0 AWG aluminum conductors meet NEC dwelling-service provisions in most cases. However, applying these sizes without verifying ampacity rules, termination limits, installation conditions, and voltage drop can lead to undersized or noncompliant installations. Below, I walk through the sizing process I use on projects and the traps that catch even experienced contractors.
Key Takeaways:
- 2/0 Cu and 4/0 Al work for qualifying residential services under NEC 310.12, but not for every 200 A feeder or commercial application.
- Termination temperature ratings often govern conductor ampacity, not insulation rating alone.
- Voltage drop becomes the limiting factor on runs longer than 100 feet, especially at full load.
- Aluminum requires anti-oxidant compound and terminals rated for AL; skipping either creates a fire hazard within two years.
- Neutral and grounding conductors follow separate sizing tables—do not assume they match the phase conductors.
What Size Wire Is Needed for a 200-Amp Service?
The answer depends on whether your installation qualifies for NEC 310.12 dwelling-service rules. If it does, you can use conductors rated for 83% of the service ampacity—166 amps for a 200 A service—which lands you at 2/0 copper or 4/0 aluminum.
If the installation does not qualify—say, a 200 A subpanel feeder or a commercial service—you size conductors using the standard ampacity tables in NEC 310.16 (now 310.15(B)(16) in recent editions). In that case, you need conductors with at least 200 A of allowable ampacity after applying adjustment and correction factors.
| Application | Copper | Aluminum |
|---|---|---|
| Qualifying 200 A dwelling service | 2/0 AWG | 4/0 AWG |
| Non-dwelling or non-qualifying 200 A circuit | Size per ampacity table | Size per ampacity table |
I've seen contractors assume 2/0 copper works for every 200 A application. It doesn't. A 200 A feeder to a detached garage or a 200 A circuit supplying a large HVAC unit requires full 200 A ampacity, and 2/0 copper at 75°C terminations provides only 175 A. You need 3/0.
How to Size and Check Wire for a 200-Amp Service
Confirm the Service Rating and Voltage
Most U.S. residential services are 120/240 V single-phase. If you're working on a 208Y/120 V multifamily service or a 240 V delta service, the conductor and grounding requirements differ. Check the utility transformer configuration before ordering wire.
Determine Whether Dwelling-Service Sizing Rules Apply
NEC 310.12 allows reduced conductor sizing for services and feeders supplying dwelling units, provided the conductors are listed and the installation meets the specified conditions. The 83% factor (200 A × 0.83 = 166 A) applies only here.
This provision does not extend to:
- Feeders to outbuildings that are not dwelling units
- Subpanels within the same dwelling if they do not qualify as a feeder supplying the entire dwelling load
- Commercial or industrial 200 A circuits
When in doubt, size for 200 A.
Verify the Electrical Load Calculation
A 200-amp service rating should come from an actual load calculation per NEC Article 220, not from the panel bus rating. I've walked jobs where the panel was rated 200 A but the calculated load was 140 A. Upsizing the service added cost without benefit. Conversely, I've also seen undersized services feeding electric vehicle chargers and heat pumps that weren't in the original load estimate.
Choose Copper or Aluminum
Copper costs more per foot but requires smaller raceways and less labor. Aluminum saves on material cost but demands careful termination practice.
From my experience, aluminum makes sense on runs longer than 50 feet or when material cost dominates labor cost. On short, high-labor installations—think tight attic or crawlspace pulls—the smaller copper size saves time and avoids conduit upsizing.
Verify Conductor Ampacity
Pull the conductor ampacity from NEC Table 310.16 (or 310.15(B)(16)) at the insulation temperature rating, then check the termination temperature rating of your equipment. Most 200 A panels and breakers have 75°C terminals, so even if you install 90°C THHN, you use the 75°C column.
For 2/0 copper at 75°C: 175 A
For 4/0 aluminum at 75°C: 180 A
These values exceed the 166 A threshold for a qualifying dwelling service, but fall short of 200 A for non-dwelling applications.
Check Termination Temperature Ratings
This is the mistake that fails inspections. A 90°C insulation rating does not allow you to use the 90°C ampacity unless both ends of the conductor terminate on equipment rated for 90°C and the installation conditions support it. Residential panels are almost always 75°C, and even when a breaker is rated 90°C, the panel bus may not be.
When I size conductors, I default to the 75°C column unless I have written confirmation that the equipment supports 90°C terminations.
Apply Required Adjustment or Correction Factors
If you're running more than three current-carrying conductors in a single raceway, apply the adjustment factors in NEC 310.15(B)(3)(a). For a standard single-phase service (two ungrounded and one neutral), you have three current-carrying conductors and no adjustment is required—unless the neutral carries significant harmonic current, in which case it counts.
Ambient temperature corrections matter in attics and outdoor installations. An attic that reaches 130°F in summer requires a correction factor that can reduce allowable ampacity by 20% or more.
Check Run Length and Voltage Drop
Ampacity and voltage drop are separate checks. A conductor can satisfy ampacity requirements and still drop too much voltage over a long run.
For a 200 A service at full load over 100 feet of 2/0 copper, I calculate roughly 2.5% voltage drop at 240 V. That's acceptable under most design guidelines. At 150 feet, it climbs to 3.75%, which is marginal. Beyond that, I upsize to 3/0 or 4/0 copper.
Aluminum drops more voltage for the same size, so I typically upsize aluminum by one or two gauge sizes on runs longer than 75 feet.
Size Neutral, Grounding Electrode, and Equipment Grounding Conductors as Applicable
The neutral conductor for a dwelling service can be sized per NEC 220.61, which allows demand factors for unbalanced loads. In practice, most residential services use a neutral that matches the ungrounded conductors, but the code does not require it.
The grounding electrode conductor is sized from NEC Table 250.66 based on the size of the service entrance conductors. For 2/0 copper service conductors, the grounding electrode conductor is 4 AWG copper.
The equipment grounding conductor, if used, is sized from NEC Table 250.122 based on the overcurrent device rating. For a 200 A breaker, that's 6 AWG copper.
These are three different conductors with three different sizing rules. Do not assume they are the same size.
Verify Local Requirements Before Installation
Some jurisdictions require copper only, or prohibit aluminum smaller than 2 AWG. Others require upsizing by one gauge size for all service conductors regardless of code-minimum values. Check with the authority having jurisdiction and the local utility before ordering materials.
Copper vs. Aluminum Wire for a 200-Amp Service
I've installed both, and each has a place.
Copper offers higher conductivity, so the conductor is smaller and easier to handle. Terminations are straightforward: strip, insert, torque. The material cost is higher, but on short runs with tight working space, the labor savings offset the price difference.
Aluminum requires more cross-sectional area for the same ampacity, so the conductors are larger and the raceway may need to upsize. Terminations require anti-oxidant compound, and the terminals must be rated for aluminum. Skip the compound, and you'll have a high-resistance connection that heats up under load. I've seen failed aluminum terminations on installations less than three years old where the installer either didn't use compound or didn't torque the lug to spec.
That said, aluminum is lighter and costs less per foot. On a 150-foot service lateral or a long overhead service drop, the weight difference matters, and the cost difference can run several hundred dollars.
| Factor | Copper | Aluminum |
|---|---|---|
| Conductivity | Higher | Lower |
| Required size for same ampacity | Smaller | Larger |
| Weight per foot | Heavier | Lighter |
| Material cost | Higher | Lower |
| Termination complexity | Lower | Higher |
| Anti-oxidant compound required | No | Yes |
When I choose aluminum:
- Service runs longer than 50 feet
- Overhead installations where weight matters
- Budget-constrained projects where material cost dominates
When I choose copper:
- Tight working spaces where bending radius and conduit fill are concerns
- Underground or wet locations where aluminum corrosion risk is higher
- Jobs where the installer's experience with aluminum terminations is uncertain
How Distance Affects 200 Amp Wire Size
Voltage drop increases with current, resistance, and distance. For a given conductor material and size, resistance per foot is fixed, so doubling the run length doubles the voltage drop.
The formula for single-phase voltage drop is:
Vd = 2 × K × I × L / CM
Where:
- Vd = voltage drop (volts)
- K = conductor resistivity constant (12.9 for copper, 21.2 for aluminum)
- I = current (amps)
- L = one-way length (feet)
- CM = circular mils
For a 200 A load on a 100-foot run of 2/0 copper (133,100 CM):
Vd = 2 × 12.9 × 200 × 100 / 133,100 ≈ 3.87 V
At 240 V, that's 1.6% voltage drop. Acceptable.
At 200 feet:
Vd ≈ 7.74 V, or 3.2%.
Still within the commonly cited 3% service and 5% total guideline, but closer to the edge.
At 300 feet:
Vd ≈ 11.6 V, or 4.8%.
Now you're marginal. Under full load, the voltage at the panel could drop below 230 V, which affects motor starting and resistive loads.
To bring it back under 3%, I upsize to 3/0 copper (167,800 CM):
Vd = 2 × 12.9 × 200 × 300 / 167,800 ≈ 9.2 V, or 3.8%.
Better, but still marginal. Upsizing to 4/0 copper (211,600 CM) drops it further:
Vd ≈ 7.3 V, or 3.0%.
That's the size I'd actually install.
Voltage drop is load-dependent. If the actual peak load is 150 A instead of 200 A, the voltage drop is proportionally lower. But I size for the rated service capacity, not the estimated load, because the service rating defines the maximum legal load.
200 Amp Service Wire Types and Installation Methods
THHN/THWN-2
THHN/THWN-2 is dual-rated for dry (THHN, 90°C) and wet (THWN-2, 90°C) locations. It's the most common choice for service conductors in raceway. I use it for nearly all conduit installations, both above and below ground.
One limitation: THHN/THWN-2 is not rated for direct burial. If you're running service conductors underground without conduit, you need a different cable type.
XHHW-2
XHHW-2 is rated for wet and dry locations at 90°C. It's common in service entrance applications and underground conduit. The insulation is thicker than THHN, which can make conduit fill tighter, but it handles moisture and sunlight better in exposed outdoor installations.
Service-Entrance Cable (Type SE)
SE cable is a factory-assembled cable with two insulated conductors and a bare neutral. It's common for overhead service drops and surface-mounted service entrances. Some local codes restrict SE cable to above-ground installations and require conduit for underground or exposed below-grade runs.
SE cable is convenient, but I avoid it in wet or underground locations unless it's specifically listed for that use. Most standard SE cable is not.
Underground Installations
Underground conduit is a wet location, so conductors must have a wet-location rating: THWN-2, XHHW-2, or equivalent.
For direct burial, use cable listed for direct burial, such as Type UF or direct-burial rated USE-2. Standard THHN or SE cable will fail underground.
I've seen contractors bury standard SE cable because it was left over from another job. Within five years, the insulation degrades and the cable fails. Don't shortcut this.
Common 200 Amp Service Wire-Sizing Mistakes
| Mistake | Why It Matters |
|---|---|
| Assuming 2/0 Cu or 4/0 Al works for every 200 A application | Dwelling-service provisions don't apply to feeders, subpanels, or commercial circuits |
| Ignoring termination temperature ratings | 90°C insulation doesn't allow 90°C ampacity if the terminal is rated 75°C |
| Using the wrong ampacity table column | Most equipment uses 75°C terminals; using the 90°C column oversizes the breaker relative to the conductor |
| Skipping adjustment factors for ambient temperature or conduit fill | High attic temperatures and multiple conductors reduce allowable ampacity |
| Not calculating voltage drop | Long runs can meet ampacity requirements but still drop excessive voltage under load |
| Using THHN in direct-burial applications | THHN is not rated for direct burial; it will fail underground |
| Installing aluminum without anti-oxidant compound | Creates high-resistance connections that overheat and fail within a few years |
| Sizing neutral and grounding conductors the same as phase conductors | Each follows different code tables and demand factors |
The most expensive mistake I've seen: a contractor installed 2/0 copper for a 200 A feeder to a detached workshop, assuming it was a dwelling service. It wasn't. The feeder supplied a 200 A subpanel with a continuous 180 A load from welding equipment. The conductors overheated, the insulation failed, and the installation had to be redone with 3/0 copper. The rework cost more than doing it right the first time.
Conclusion
Sizing wire for a 200-amp service comes down to three questions: Does the installation qualify for NEC 310.12 dwelling-service rules? What are the termination temperature ratings? What's the run length?
For a standard residential service under 100 feet, 2/0 copper or 4/0 aluminum works in most cases. Beyond that, check voltage drop and upsize as needed. For feeders, subpanels, and commercial applications, size conductors to provide at least 200 A of allowable ampacity after applying correction and adjustment factors.
The code provides minimum requirements. On long runs, high-load installations, or projects where future capacity matters, I upsize by one gauge as a matter of practice. The cost difference is small, and the performance margin is worth it.
