How to Size Wire for a 200 Amp Service: NEC Requirements and Worked Examples

A typical qualifying 200 A dwelling service can use 2/0 AWG copper or 4/0 AWG aluminum conductors under the NEC dwelling-service provisions. However, these sizes do not apply automatically to every 200 A service or feeder. The correct conductor size depends on whether NEC 310.12 applies, required ampacity, conductor and terminal temperature ratings, adjustment factors, installation conditions, and voltage drop. This guide explains how to evaluate these requirements using practical sizing examples.

Catalog

Figure 1. Copper and Aluminum Service-Entrance Conductors for a 200 Amp Electrical Service

What Size Wire Is Needed for a 200 Amp Service?

For a qualifying 200 A dwelling service or whole-dwelling feeder, NEC 310.12 permits 2/0 AWG copper or 4/0 AWG aluminum or copper-clad aluminum conductors when the applicable conditions are met. [1]

Standard 200 Amp Residential Service Sizes

Conductor Material	Common Size for a Qualifying 200 A Dwelling Service or Feeder
Copper	2/0 AWG
Aluminum or Copper-Clad Aluminum	4/0 AWG

These sizes come from the dwelling-service provisions of NEC 310.12. They should not be treated as universal conductor sizes for every 200 A circuit, feeder, or service. [1]

When These Sizes Apply

The 2/0 AWG copper and 4/0 AWG aluminum or copper-clad aluminum sizes apply only when the installation qualifies under NEC 310.12. This generally includes a single-phase dwelling service supplying the entire dwelling load and a qualifying feeder supplying the entire dwelling load. A feeder serving only part of a dwelling, such as a garage or subpanel feeder, does not qualify simply because it is installed at a residence. [1]

Before using the NEC dwelling-service sizing table, verify the NEC edition adopted locally and confirm that the conductor or cable has the required insulation temperature rating. Ambient temperature, conductor grouping, terminal ratings, and other correction or adjustment factors can also require a larger conductor. [1]

Why a 200 Amp Service Does Not Always Use a 200 Amp Conductor Ampacity

For qualifying dwelling services and whole-dwelling feeders, NEC 310.12 allows conductor sizing using the 83% provision rather than requiring the conductor’s standard ampacity to equal the full 200 A service rating. [1]

This provision is why certain conductor sizes with standard ampacities below 200 A may still be permitted for a qualifying 200 A dwelling installation. The 83% calculation and conductor-selection requirements are explained in Section 2.2.

How to Size a 200 Amp Service Wire Correctly

Sizing a 200 A service conductor requires more than choosing a standard wire size. First confirm whether the dwelling-service provisions apply, then check ampacity, temperature ratings, correction or adjustment factors, voltage drop, and the installation method.

The applicable NEC edition, local amendments, utility rules, and AHJ requirements should also be verified.

Determine Whether It Is a Service or Feeder

NEC 310.12 applies only to qualifying single-phase dwelling services and whole-dwelling feeders rated 100–400 A. [1]

Installation	Can NEC 310.12 Apply?
Service supplying the entire one-family dwelling	Yes, if requirements are met
Feeder supplying the entire dwelling load	Potentially yes
Detached-garage feeder	Normally no
Partial-load subpanel	No
Commercial 200 A service	No

A conductor does not qualify for dwelling-service sizing simply because it is installed in a house or protected by a 200 A breaker.

Verify the Required Ampacity

For a qualifying 200 A dwelling service or whole-dwelling feeder under NEC 310.12:

Required ampacity = 200 A × 0.83 = 166 A [1]

At 75°C, 2/0 AWG copper is rated 175 A, while 4/0 AWG aluminum or copper-clad aluminum is rated 180 A, so both exceed the 166 A requirement under qualifying conditions. [1]

These sizes should not be used automatically for every 200 A installation. Verify the locally adopted NEC edition, conductor insulation rating, terminal temperature rating, and any required correction or adjustment factors before making the final selection. [1]

Check Conductor and Terminal Temperature Ratings

For circuits over 100 A, equipment terminations are generally based on the 75°C ampacity column unless the equipment is specifically identified for another rating. [1]

A 90°C-rated conductor may be used when applying permitted correction or adjustment factors, but its final allowable ampacity must still comply with the applicable terminal limitation.

In practice:

• verify conductor insulation rating;

• verify terminal temperature rating;

• apply required correction or adjustment factors;

• confirm the final ampacity does not exceed the terminal limit.

Apply Temperature and Ampacity Adjustment Factors

Ampacity may need to be reduced for conditions such as high ambient temperature, multiple current-carrying conductors, cable or conductor arrangements covered by NEC 310.15. [1]

For example, a 90°C-rated 2/0 copper conductor has a 195 A ampacity. With a 0.82 correction factor:

195 A × 0.82 = 159.9 A

Because 159.9 A is below the required 166 A, 2/0 copper would not be sufficient in this example. A larger conductor may therefore be required. [1]

Check Distance and Voltage Drop

A conductor can meet ampacity requirements but still have excessive voltage drop on a long run.

For a simplified single-phase calculation:

V_D = (2 × K × I × L) ÷ CM

where V_D is voltage drop, K is conductor resistivity, I is current, L is one-way length, and CM is conductor area.

Voltage drop increases with current and distance and generally decreases with larger conductor size. Long runs may therefore justify using a conductor larger than the minimum ampacity-based size.

NEC informational material commonly references 3% for a feeder or branch circuit and 5% for the combined feeder and branch-circuit path as design guidance, not as a universal mandatory sizing rule. [1]

See Section 4.2 for a long-run example.

Match the Conductor to the Installation Method

The conductor must also be listed for the installation environment.

• Underground raceway: use conductors rated for wet locations. [1]

• Overhead service: use a permitted conductor and wiring method.

• Raceway: verify conductor type and conduit fill.

• Cable assemblies: confirm the cable is permitted for the location.

• Aluminum conductors: verify terminal and connector compatibility.

Select the conductor based on electrical requirements first, then verify raceway size, bending space, physical protection, and installation conditions.

Copper vs Aluminum for a 200 Amp Service

Figure 2. Copper and Aluminum Conductors Used for 200 Amp Residential Service

For context, a common comparison for a qualifying 200 A dwelling service is 2/0 AWG copper versus 4/0 AWG aluminum. This section focuses on how the two conductor materials differ in resistance, physical size, weight, cost, termination requirements, and installation.

Comparison	2/0 AWG Copper	4/0 AWG Aluminum	Meaning
Common qualifying dwelling size	2/0 AWG	4/0 AWG	Aluminum generally requires a larger conductor size than copper for comparable applications.
AC resistance at 75°C	About 0.097 Ω/1,000 ft	About 0.100 Ω/1,000 ft	At these respective sizes, resistance is very similar. A same-size copper conductor would generally have lower resistance than aluminum.
Approximate conductor outside diameter	0.524 in	0.591 in	The larger aluminum conductor requires more physical space. Check raceway fill, bending space, and terminal capacity.
Approximate finished conductor weight	452 lb/1,000 ft	247 lb/1,000 ft	The aluminum conductor is about 45% lighter in this comparison, which can make handling and pulling easier.
Conductor cost	Generally higher	Generally lower	Aluminum can reduce material cost for large conductors. Actual pricing varies with supplier, conductor type, and metal prices. [4]
Terminal compatibility	Use terminals identified for copper where applicable	Use terminals identified for aluminum or the applicable conductor material	Verify equipment and connector markings rather than assuming compatibility based on physical fit. [1]
Termination preparation	Follow specified conductor preparation and terminal torque	Follow specified preparation, compatible-terminal, and torque requirements	Proper installation is important for both materials. Follow manufacturer instructions regarding oxide-inhibiting compound rather than treating it as universally required. [1,4]
Corrosion considerations	Generally less sensitive to connection-related oxidation issues	Requires careful use of compatible materials and proper connection preparation	Listed connectors and manufacturer installation procedures are especially important for reliable aluminum terminations. [4]
Space requirements	Smaller conductor can simplify routing and termination	Larger conductor may require more raceway and terminal space	Check conduit fill, bending space, and the equipment's permitted conductor-size range.
Practical selection	Useful where compact routing or copper-specific equipment is important	Useful where lower conductor weight and material cost are priorities	Consider installed cost, available space, conductor length, voltage drop, equipment compatibility, and local requirements.

Example data note: The resistance, diameter, and weight values above compare Southwire SIMpull XHHW-2 copper and aluminum conductors from the same general product family. Dimensions and weights can vary between manufacturers and conductor constructions. [2,3]

Worked 200 Amp Service Sizing Examples

The correct conductor size for a 200 A installation depends on what the conductor supplies, the installation conditions, and the design requirements. The following examples show why a qualifying dwelling service can use a different conductor size from a long service run or an ordinary 200 A feeder.

These examples assume 75°C-rated or higher conductors and equipment suitable for the stated conductor sizes. Actual installations must also follow the NEC edition adopted locally, utility requirements, equipment listings, and requirements of the authority having jurisdiction. [1]

Case 1: Typical 200 Amp Residential Service

Figure 3. Typical Residential Main Service Panel with Service-Entrance Conductors

Assumptions:

• single-family dwelling;

• 120/240 V, single-phase service;

• service conductors supply the entire dwelling load;

• 200 A service rating;

• short conductor run;

• no correction or adjustment factors;

• voltage drop is not a limiting factor.

Because the conductors supply the entire dwelling load, NEC 310.12(A) can apply. [1]

From Section 2.2, the required minimum ampacity for this qualifying 200 A service is 166 A.

Material	Conductor Size	75°C Ampacity	Meets 166 A Requirement?
Copper	2/0 AWG	175 A	Yes
Aluminum or copper-clad aluminum	4/0 AWG	180 A	Yes

Therefore, under these assumptions, the qualifying 200 A dwelling service can use 2/0 AWG copper or 4/0 AWG aluminum/copper-clad aluminum. [1]

This result applies only when the installation qualifies under NEC 310.12 and the applicable installation conditions do not require a larger conductor.

Case 2: Long Underground Service Run

Consider a qualifying 200 A dwelling service with a long underground run.

Assumptions:

• 200 A single-family dwelling service;

• 120/240 V, single phase;

• 300 ft one-way conductor length;

• aluminum conductors;

• XHHW-2 conductors in underground raceway;

• representative operating load of 160 A;

• no additional ampacity correction or adjustment factors;

• voltage-drop comparison based on the 240 V line-to-line circuit.

From Section 2.2, 4/0 AWG aluminum satisfies the assumed minimum ampacity requirement for this qualifying service. However, the 300 ft distance makes voltage drop an important design consideration.

For a simplified resistance-based estimate:

VD ≈ 2 × I × L × R ÷ 1000

Southwire lists approximately 0.100 Ω/1,000 ft at 75°C for 4/0 aluminum XHHW-2 and 0.071 Ω/1,000 ft for 300 kcmil aluminum. [3]

Conductor	Simplified Estimated Voltage Drop	Percentage at 240 V
4/0 AWG aluminum	9.6 V	4.0%
300 kcmil aluminum	6.82 V	2.84%

These 9.6 V and 6.82 V values are simplified estimates for the stated 240 V line-to-line, 160 A example. Increasing the conductor from 4/0 AWG to 300 kcmil aluminum reduces the estimated voltage drop by about 29%.

The key point is that 4/0 aluminum meets the assumed ampacity requirement, while 300 kcmil aluminum may be selected to improve voltage performance over the long run. The larger conductor is therefore a voltage-drop design choice, not a correction for insufficient ampacity.

Actual AC voltage drop can differ from this simplified resistance-only estimate because it also depends on factors such as conductor reactance and load power factor. The 3% value may be used as a design target in appropriate applications, but it should not be presented as a universal mandatory limit for all service conductors. [1]

Neutral, Grounding, and Other Conductors in a 200 Amp Service

The ungrounded service conductors are only part of a 200 A installation. The neutral, grounding electrode conductor, and any equipment grounding conductor have different functions and are sized under different NEC rules. They should not be assumed to have the same size simply because they are part of the same electrical system. [1]

Does the Neutral Have to Be the Same Size?

No. The neutral does not automatically have to be the same size as the ungrounded service conductors.

For a typical 120/240 V single-phase dwelling service, the neutral carries the unbalanced portion of the line-to-neutral loads. Loads connected directly from line to line at 240 V do not normally add to the neutral load. Under the 2026 NEC, Section 120.61 defines the feeder or service neutral load based on the maximum calculated unbalance between the neutral and any ungrounded conductor. [1]

For example, a house can have a 200 A service while its calculated neutral load is substantially less than 200 A because many major appliances, such as some water heaters, ranges, EV chargers, and HVAC equipment, operate at 240 V.

However, this does not mean that the neutral can be reduced to any convenient size. The final neutral conductor must satisfy all applicable requirements, including: the calculated neutral load, permitted demand factors or reductions, conductor ampacity requirements, nonlinear-load requirements where applicable, and minimum grounded service-conductor sizing and bonding requirements.

For service equipment, NEC 250.24 also establishes minimum requirements for the grounded service conductor used as part of the service grounding and bonding system. [1]

Therefore, a statement such as “a 200 A service always uses a ___ AWG neutral” is not technically reliable. The neutral must be calculated for the actual installation.

Grounding Electrode Conductor Sizing

The grounding electrode conductor (GEC) connects the service grounding system to the grounding electrode system, which can include electrodes such as metal underground water piping, concrete-encased electrodes, ground rods, building steel, and ground rings.

For an AC service, NEC Table 250.66 generally sizes the GEC according to the largest ungrounded service-entrance conductor or equivalent area of parallel conductors, not simply from the 200 A service rating. [1]

For the conductor sizes commonly used for a qualifying 200 A dwelling service: [1]

Ungrounded Service Conductors	Base GEC Size from Table 250.66
2/0 AWG copper	4 AWG copper or 2 AWG aluminum/copper-clad aluminum
4/0 AWG aluminum or copper-clad aluminum	4 AWG copper or 2 AWG aluminum/copper-clad aluminum

This table value is only the starting point because NEC 250.66 includes electrode-specific rules. [1]

For example:

• Rod, pipe electrode, or plate electrode: where the conductor connects only to these qualifying electrodes and does not continue to another electrode requiring a larger conductor, the GEC is not required to be larger than 6 AWG copper or 4 AWG aluminum/copper-clad aluminum. [1]

• Concrete-encased electrode: the conductor is not required to be larger than 4 AWG copper under the applicable rule. [1]

• Ground ring: the GEC is not required to be larger than the conductor used for the ground ring. [1]

These exceptions explain why the statement “every 200 A service requires a #4 copper grounding electrode conductor” is incomplete. The correct size depends on both the service-conductor size and the type and arrangement of grounding electrodes.

If several grounding electrodes are present, NEC requirements for the complete grounding electrode system must be followed rather than selecting a conductor size based on only one electrode. [1]

Equipment Grounding vs Grounding Electrode Conductors

A grounding electrode conductor and an equipment grounding conductor are not the same conductor and should not be sized from the same table. [1]

Conductor	Main Function	Typical Sizing Basis
Grounding electrode conductor (GEC)	Connects the service grounding/bonding system to the grounding electrode system	Largest ungrounded service conductor, using Table 250.66 and its electrode-specific rules
Equipment grounding conductor (EGC)	Provides an effective ground-fault current path for equipment and downstream circuits	Rating or setting of the upstream overcurrent protective device, using Table 250.122
Neutral/grounded conductor	Carries normal unbalanced load current	Calculated neutral load plus applicable minimum service grounded-conductor requirements

For example, on a 200 A feeder protected by a 200 A overcurrent device, Table 250.122 generally specifies a minimum wire-type equipment grounding conductor of 6 AWG copper or 4 AWG aluminum/copper-clad aluminum. If the ungrounded feeder conductors are increased in size under conditions covered by NEC 250.122(B), the equipment grounding conductor may also need to be increased. [1]

This equipment grounding conductor should not be confused with the grounding electrode conductor at the service.

At the service disconnect, the grounded service conductor, grounding electrode system, and service equipment are bonded as required by the NEC. On the load side of the service disconnect, the neutral and equipment grounding conductors are generally kept separate except where a specific NEC provision permits otherwise. [1]

The practical rule is simple: do not select the neutral, grounding electrode conductor, or equipment grounding conductor by copying the size of another conductor. Each has its own sizing method and electrical purpose.

Common 200 Amp Service Sizing Mistakes

Common errors include:

• Using 2/0 AWG copper or 4/0 AWG aluminum for every 200 A installation. These sizes apply only when the dwelling-service provisions are applicable.

• Applying dwelling-service sizing to nonqualifying feeders. Detached-building, subpanel, and partial-load feeders may require different sizing.

• Sizing only from the 200 A rating. Apply the correct ampacity rules for the specific installation.

• Ignoring terminal temperature ratings. Do not automatically use the conductor’s highest temperature rating for ampacity.

• Ignoring correction and adjustment factors. Installation conditions can reduce allowable ampacity.

• Checking ampacity but not voltage drop. Long runs may require a larger conductor.

• Using unsuitable conductors underground. Underground raceways require conductors rated for wet locations.

• Using incompatible terminals with aluminum conductors. Verify that terminals are identified for the conductor material.

• Sizing neutral and grounding conductors like the service conductors. These conductors follow separate NEC sizing rules.

• Relying on generic wire-size charts. Verify conductor material, temperature rating, installation method, distance, and applicable NEC requirements.

Conclusion

A 200 A service does not have one universal conductor size. First determine whether the dwelling-service sizing provision applies, then verify the required ampacity, temperature and installation conditions, and any correction or adjustment factors. For long runs, also evaluate voltage drop before finalizing the conductor size. The final design should comply with the applicable NEC edition, local requirements, utility rules, and AHJ requirements.

Technical References

[1] National Fire Protection Association. “NFPA 70, National Electrical Code.” National Fire Protection Association, 2026. NFPA 70, 2026 Edition.

[2] Southwire Company, LLC. “SIMpull XHHW-2®/RW90 Copper.” Southwire Company, LLC, n.d. SPEC 10006. Accessed September 29, 2026.

[3] Southwire Company, LLC. “SIMpull XHHW-2®/RW90 Aluminum with AlumaFlex® Brand Conductors.” Southwire Company, LLC, n.d. SPEC 10015. Accessed September 29, 2026.

[4] Yuhsin Hawig and Radek Kochanowski. “10 Things You Must Know About Building Wire Products.” Southwire Company, LLC, 2024. R³e Edition 32, Volume 1.

[5] Southwire Company, LLC. “Re³™ Voltage Drop Calculator.” Southwire Company, LLC, n.d. Accessed September 29, 2026.

Frequently Asked Questions [FAQ]

1. Does the NEC 83% rule mean a 200 amp home can only use 166 amps?

No. The 166 A value is a conductor-sizing allowance for qualifying dwelling services and feeders. It does not reduce a 200 A service rating to 166 A or set the home's maximum usable load at 166 A. [1]

2. What is the difference between a service load calculation and a wire ampacity calculation?

A service load calculation determines how much electrical capacity the building needs. Conductor ampacity calculations determine whether the selected wire can safely carry that required load. Under the 2026 NEC, dwelling and service load calculations are primarily covered in Article 120. [1]

3. What happens if the calculated dwelling load is greater than 200 amps?

Correctly sized 200 A conductors do not solve an overloaded service. If the calculated load exceeds the permitted service capacity, the design may require a larger service or an approved load-management method where the NEC allows one. [1]

4. Can adding an EV charger require changes to an existing 200 amp service?

Yes. An EV charger adds load that must be considered when checking whether the existing service has enough capacity. In some installations, an approved energy-management system can limit EV charging demand and reduce the maximum load placed on the service. [1]

5. Can two smaller wires be connected in parallel for a 200 amp service instead of using one large conductor?

Parallel conductors are permitted in qualifying installations, but they cannot simply be any two smaller wires whose ampacities add to 200 A. NEC rules generally require paralleled conductors to be 1/0 AWG or larger and to meet requirements for matching length, material, size, insulation, and termination. [1]