Service Entrance Conductors for 200A Service: NEC Requirements, Burial Depth, and Sizing

The standard answer to “what size service entrance wire for 200A residential?” is 2/0 copper or 4/0 aluminum. That answer is correct for a dwelling, but it’s not the answer Table 310.16 alone would give — the 75°C ampacity column lists 175A for 2/0 copper and 180A for 4/0 aluminum, both below the 200A service rating.

The discount comes from NEC 310.12, often called the 83% rule. It applies specifically to service entrance and main feeder conductors in dwelling units, and missing it is a common cause of oversized service installs that waste copper and money.

This guide covers when 310.12 applies, when it doesn’t, how to size for longer-than-typical runs, and what changes for underground service. Use the wire size calculator to verify the result against your specific NEC edition and AHJ requirements.

The 83% Rule (NEC 310.12)

NEC 310.12 (titled “Single-Phase Dwelling Services and Feeders”) lets service entrance and main feeder conductors in dwelling units be sized at 83% of the service rating instead of the full 100%. For a 200A service:

The rule exists because dwelling loads are diversified — not every appliance runs at once — and the demand factors in NEC Article 220 (Article 120 in the 2026 NEC) already account for that diversity in calculating connected load. Sizing service conductors at 100% on top of demand-factored load would be doubly conservative.

310.12 only applies when:

• The installation is a dwelling unit (one- and two-family dwellings, individual units in multifamily occupancy with their own service or feeder).
• The conductors are service entrance conductors or the main feeder from the service to the main panel.
• The system is single-phase, 120/240V.
• The conductor carries 100% of the diversified load for the dwelling.

Outside those conditions — commercial service, multifamily house panel, three-phase — you size to the full service rating per Table 310.16, not 83%.

2/0 Copper or 4/0 Aluminum: The Standard Sizes

From NEC Table 310.16, 75°C column (the standard column for THWN-2 service entrance cable):

• 2/0 AWG copper: 175A — satisfies the 166A minimum.
• 4/0 AWG aluminum: 180A — satisfies the 166A minimum.
• 3/0 AWG copper: 200A — satisfies the full 200A general rule (no 83% discount needed).
• 250 kcmil aluminum: 205A — satisfies the full 200A general rule.

For a typical dwelling, 2/0 copper or 4/0 aluminum is the right answer. Using 3/0 copper or 250 kcmil aluminum on a residential service is over-engineering — you’re paying for the larger conductor and the larger lugs, breakers, and pulling equipment without code benefit.

The General-Ampacity Path: NEC Table 310.16

Outside dwelling-service applications, you size service-entrance conductors directly from Table 310.16 at the conductor’s temperature rating. For a 200A service to a small commercial building or to a multifamily house panel:

• 3/0 AWG copper (75°C, THWN-2): 200A — meets the rating exactly.
• 250 kcmil aluminum (75°C, THWN-2): 205A — meets the rating with 5A margin.

NEC 110.14(C) restricts terminations on most modern equipment (rated 100A and over) to the 75°C ampacity column even when the conductor itself is 90°C-rated. You can use the 90°C column for derating math (temperature correction, conduit fill adjustment), but the final ampacity is capped at the 75°C value at the termination.

For 200A service, 110.14(C) means the practical sizing column is always 75°C, regardless of whether you’re using 75°C or 90°C insulation. The 90°C insulation buys you derating margin, not larger ampacity at the lugs.

When to Upsize for Distance (Voltage Drop)

The 200A service to a typical detached house panel is 20–50 feet from meter to main panel. Voltage drop is rarely the controlling factor at those distances. But for a long service run — meter at the road, panel in a barn 250 feet away — voltage drop can drive a one- or two-size upsize.

For a 200A residential service at 240V single-phase, NEC 210.19(A) Informational Note recommends keeping voltage drop under 3% on branch circuits and 5% total. The service entrance counts toward the 5% total. Using the standard voltage drop formula for single-phase:

Voltage drop is advisory in the NEC, not mandatory — but most AHJs treat the 3%/5% recommendation as enforceable for service entrance work. Confirm with the local inspector before sizing right at the recommendation ceiling.

Underground Service: Burial Depth and Conductor Type

For underground service entrance, NEC Table 300.5(A) governs minimum burial depths:

• Direct burial (USE/USE-2 cable): 24 inches.
• In rigid metal conduit (RMC) or intermediate metal conduit (IMC): 6 inches.
• In nonmetallic raceway (PVC) approved for direct burial: 18 inches.
• Under a concrete-encased duct bank (2 in min concrete): 6 inches.
• Under a building: in raceway only.

USE-2 (Underground Service Entrance, type 2) is the standard direct-burial conductor for residential service. It’s rated 90°C wet, sized from the 75°C column for ampacity per 110.14(C) at the lugs.

If the service entrance enters the building from underground and the conductors transition from USE to indoor wiring, the splice has to be in an approved enclosure (usually the meter base) — you can’t splice USE inline underground without an approved direct-bury splice kit, and you can’t run USE inside the building beyond the service entrance per 338.10(B).

Sanity Check / Spot Check

• Service is dwelling, single-phase, 120/240V? → 310.12 applies, use 83% rule (2/0 Cu / 4/0 Al for 200A).
• Run length is over 100 ft? → Check voltage drop, upsize if over 3% on the service.
• Underground? → Verify burial depth per 300.5(A) and conductor type (USE-2 for direct burial, dual-rated 75°C/90°C for in-conduit).
• Ungrounded conductors sized? Don’t forget the grounded (neutral) conductor — NEC 250.24(C) requires it sized to carry the maximum unbalanced load, with a minimum from Table 250.66.
• Grounding electrode conductor sized from Table 250.66? For 2/0 copper service: #4 copper GEC. For 4/0 aluminum service: #2 copper GEC (the GEC is sized from the largest service entrance conductor).

For the broader copper-vs-aluminum decision — including termination compatibility, anti-oxidant compound requirements, and AHJ acceptance — see the NEC wire size copper vs aluminum reference. For the upstream sizing of branch circuits and feeders downstream of the main panel, wire sizing for circuit breakers under the NEC covers Article 240 OCPD coordination and the “next size up” rule.

Authoritative source: NFPA 70 (NEC). AHJ-specific amendments may apply — verify before installation.