The quick answer
A 400 amp residential service needs 400 kcmil copper or 600 kcmil aluminum as a single run, using the NEC dwelling rule (310.12). In practice, most 400 amp homes are wired as two parallel 200 amp sets instead — 2 × 2/0 copper or 2 × 4/0 aluminum per leg. The equipment ground is 3 AWG copper, and the wire to your ground rods is just 6 AWG copper.
Single run: 400 kcmil copper (or 600 kcmil aluminum). Or the common route — two sets of 2/0 copper / 4/0 aluminum feeding two 200 amp panels. Either way the equipment ground is 3 AWG copper. This is utility-coordinated, permitted work — loop in your AHJ and power company.
Why 400 kcmil works (the 83% dwelling rule)
A 400 amp commercial load would need a much bigger conductor — so why does a house get 400 kcmil? Because homes get a break. NEC 310.12 lets a dwelling's main service conductors carry only 83% of the service rating, since a house never pulls its full nameplate for long. That drops a 400 amp service down to a 400 kcmil copper (or 600 kcmil aluminum) conductor.
It lines up with the hardware, too: most residential "400 amp" meter-mains are actually rated class 320 — 320 amps continuous (400 amp). The 83% rule and the 320 amp rating are two ways of saying the same thing.
400 amp service wire size chart
Every conductor for a 400 amp dwelling service, both ways it's commonly run:
| Conductor | Copper | Aluminum |
|---|---|---|
| Hots — single run (310.12) | 400 kcmil | 600 kcmil |
| Hots — two 200A parallel | 2 × 2/0 | 2 × 4/0 |
| Neutral (220.61) | sized to load | sized to load |
| Equipment ground / EGC (250.122) | 3 AWG | 1 AWG |
| Electrode conductor / GEC (250.66) | 1/0 (6 to rods) | — |
The two hot rows are the same 400 amps done two ways: one big conductor, or two 200 amp sets sharing the load. The ground details come from our ground wire size guide.
Single conductor vs two 200A runs (parallel)
Here's the practical truth most pages skip: a residential 400 amp service is usually run as two parallel 200 amp sets, not one 400 kcmil monster. The reason is simple — a 400 amp service almost always feeds two 200 amp panels (or a 400 amp meter-main with two 200 amp mains), so two 200 amp conductor runs fall out naturally.
Two smaller sets are also cheaper, easier to bend, and easier to pull than one 400 kcmil cable. The one rule: paralleled conductors must be identical in size, type, and length (NEC 310.10(H)) so the current splits evenly between them.
Two 200 amp services you already understand, run twice: 2 × 2/0 copper or 2 × 4/0 aluminum, each set matched. It's the same wire a 200 amp service uses — just doubled.
Neutral and ground for a 400A service
The neutral is sized to the unbalanced load, not the full 400 amps (NEC 220.61) — 240-volt loads like a range, dryer, AC, or EV charger carry no neutral current, so the neutral is usually a size or two smaller than the hots. The equipment ground is 3 AWG copper (250.122). The grounding-electrode conductor to your water pipe or Ufer is about 1/0 copper (250.66) — but the wire that runs only to the ground rods caps at 6 AWG copper. See the ground wire size guide for the full grounding picture.
Copper vs aluminum for a 400A service
At this size, aluminum is the cost pick and it's completely standard — service-entrance and URD cable for big residential services is almost always aluminum (600 kcmil single, or 2 × 4/0 in parallel). Copper is smaller for the same amps but far more expensive, so it's usually reserved for tight conduit fills or where the run demands it. Aluminum needs the usual termination care — rated lugs and anti-oxidant where required. The AWG ampacity chart has the conductor numbers behind this.
Service conductors are usually short, but a long lateral to a detached home, barn, or shop can drift. At a full 320 amp load, 400 kcmil copper holds under 3% for about 350 ft — go past that and you step up a size. The Voltage Drop Calculator checks your exact run.
Common 400A service mistakes
The big one is sizing at 100% instead of the 83% dwelling rule — that over-buys the conductor and the money. Close behind: mismatched parallel sets (different length or size, which isn't allowed and makes the current split unevenly). Others: undersizing the neutral or ground; forgetting voltage drop on a long service lateral to a detached home or shop; and treating a commercial 400 amp load like a dwelling — non-dwelling services don't get the 83% break. Service work is utility-coordinated and permitted, so loop in your POCO and AHJ early.
Frequently asked questions
Wire & CircuitWhat size wire for a 400 amp service?
Wire & CircuitCan you use two 200 amp wires for a 400 amp service?
Wire & CircuitWhat size aluminum wire for a 400 amp service?
Code & SafetyWhat is the 83% rule for a 400 amp service?
Code & SafetyWhat size ground wire for a 400 amp service?
Wire & CircuitWhat size neutral for a 400 amp service?
Code & SafetyIs a 400 amp service really 320 amps?
Wire & CircuitHow many 200 amp panels can a 400 amp service feed?
This guide is for general information based on the National Electrical Code. Service sizing varies by NEC edition, your local authority having jurisdiction (AHJ), and your utility, and a service upgrade is permitted, inspected, and utility-coordinated work. Electrical work can be dangerous, so when in doubt, hire a licensed electrician.