What Size Wire for a 100 Amp Service?

Short answer: for a 100 amp residential service (single-phase 120/240 V), NEC Table 310.12 allows 4 AWG copper or 2 AWG aluminum service-entrance conductors. The grounding electrode conductor is typically 8 AWG copper, which must be protected by raceway or armor; 6 AWG copper may run exposed only where it isn't subject to physical damage (250.64(B)). For anything other than a whole-dwelling service or main feeder, size from Table 310.16 instead: 3 AWG copper or 1 AWG aluminum.

Two answers, depending on what you're feeding

The 83% rule in Table 310.12 exists because a whole house never draws its full service rating at once. It allows service conductors with an ampacity of at least 83% of the service rating. It only applies when the conductors carry the entire load of a single-phase dwelling. A 100 A feeder to a garage subpanel doesn't qualify; see 100 amp subpanel wire size.

Where the 4 AWG and 2 AWG come from

100 A × 0.83 = 83 A. In the 75°C column of Table 310.16, 4 AWG copper is rated 85 A and 2 AWG aluminum is rated 90 A. Both clear 83 A; the next sizes down (6 AWG copper at 65 A, 3 AWG aluminum at 75 A) don't. The ampacity chart has the full column.

Service-entrance cable and raceway

• SE cable. Aluminum SEU (two insulated conductors wrapped by a bare concentric neutral) is the common overhead-mast and meter-to-panel cable for a 100 A service. SER adds an insulated neutral and is used where the cable continues as a four-wire feeder.
• Conduit. Three 4 AWG copper THHN/THWN-2 conductors (two hots and a full-size neutral) total 0.2472 in², which fits 1" EMT or 1" PVC Schedule 40 at 40% fill. ¾" is too small. Aluminum XHHW-2 uses different areas from Chapter 9 Table 5; check them before choosing a trade size.
• Reduced neutral. The service neutral may be smaller than the hots when the calculated neutral load allows it (220.61), but not smaller than the size 250.24(C) requires.

Grounding and bonding

• Grounding electrode conductor (GEC), from Table 250.66: with 2 AWG or smaller copper (1/0 or smaller aluminum) service conductors, the GEC is 8 AWG copper or 6 AWG aluminum. An 8 AWG GEC must be protected by raceway or armor; many installers use 6 AWG copper so it can run exposed where not subject to damage (250.64(B)).
• To a ground rod: the GEC never needs to be larger than 6 AWG copper (250.66(A)). A single rod must be supplemented by a second electrode unless it's shown to meet 25 ohms or less (250.53(A)(2)).
• Main bonding jumper: sized from Table 250.102(C)(1), based on the service conductors. The neutral-to-ground bond is made here and nowhere downstream.
• Intersystem bonding termination for phone, cable and satellite grounds is required at the service (250.94).

Voltage drop on a service

Services are short, so voltage drop rarely controls. A 30-foot meter-to-panel run at an 80 A load drops 1.48 V on 4 AWG copper (2 × 12.9 × 80 × 30 ÷ 41,740) and 1.53 V on 2 AWG aluminum, both about 0.6% at 240 V. Long underground laterals are usually the utility's responsibility, but check where the point of service is.

Is 100 amps enough?

Many older homes and small houses with gas appliances run fine on 100 A. It becomes tight when you add an EV charger, heat pump, electric range or hot tub. Before upgrading, run a load calculation: it often shows room for a moderate EV charger, or points to an energy management system (220.70 in the 2023 NEC) as an alternative to a new service. In the 2026 NEC, the load calculation rules move to Article 120; Table 310.12 still sets the conductor size once the service rating is chosen. If the answer is an upgrade, the 200 amp service page covers the conductors.

Copper or aluminum for a 100 A service?

Aluminum SE cable dominates residential services because it is lighter and usually costs less than the equivalent copper, even one size larger. The trade-offs are at the terminations: lugs must be marked AL/CU, connections must be torqued to the manufacturer's value (110.14(D) requires an approved means, such as a torque tool, to reach the marked value), and many electricians apply antioxidant compound where the lug maker recommends it. Copper makes sense in tight meter-base or panel gutters where a smaller, more flexible conductor is easier to land. Compare current supplier prices before assuming either is cheaper for your run.

Common mistakes inspectors flag

• 4 AWG aluminum on a 100 A service. That's the copper size; aluminum needs 2 AWG.
• Applying the 83% rule to a subpanel feeder or a commercial service.
• Unprotected 8 AWG GEC running exposed along a wall.
• Neutral and ground bonded again at a downstream panel.
• Single ground rod with no second electrode or test result.

Frequently asked questions

Can I use 4 gauge aluminum for a 100 amp service?

No. Table 310.12 requires 2 AWG aluminum for a 100 A dwelling service. 4 AWG is the copper size.

What size wire from the meter to the panel for 100 amps?

The same service-entrance conductors: 4 AWG copper or 2 AWG aluminum for a dwelling, typically as SE cable or in conduit.

What size ground wire for a 100 amp service?

8 AWG copper GEC (protected), or 6 AWG copper if run exposed. Equipment grounding conductors for a 100 A feeder are 8 AWG copper or 6 AWG aluminum (Table 250.122).

Is 100 amp service enough for an EV charger?

Often, if the charger is set to a moderate current and the house has gas heat and cooking. A load calculation decides it; an energy management system or a charger with load sensing can let a 100 A service carry an EV without an upgrade.

Does 2 AWG aluminum work for a 100 amp subpanel?

Only at 90 A in the 75°C column. For a 100 A subpanel you need 1 AWG aluminum, unless the 240.4(B) next-size-up rule applies and the calculated load is 90 A or less.

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Last updated: October 6, 2026. Based on NEC 2023 Tables 310.12, 250.66 and 250.122. Service work usually requires a permit and utility coordination. Check results against the code edition and local amendments your jurisdiction enforces and with the AHJ; electrical work should be done by qualified people.