ADU / In-Law Suite Wiring: Complete Wiring Guide
Bill of materials
An ADU (accessory dwelling unit) is electrically a separate dwelling and must meet the same code requirements as a full house: separate subpanel, kitchen circuits, bathroom circuits, and a load calculation per NEC 220.82. Whether attached or detached determines feeder and grounding requirements.
ADUs require a full load calculation per NEC 220.82 (optional method) or 220.40 (standard method). Minimum circuits: two 20A kitchen small-appliance circuits, one 20A bathroom circuit, one 20A laundry circuit. All kitchen and bathroom receptacles require GFCI. All habitable rooms require AFCI. A detached ADU needs a separate grounding electrode per 250.32. Check with your utility about whether the ADU needs a separate meter.
60A subpanel (studio ADU)
| Component | Specification | NEC basis |
|---|---|---|
| Wire (copper) | 6 AWG THHN | Table 310.16, 110.14(C) |
| Wire (aluminum alt.) | 4 AWG THHN | Table 310.16, 110.14(C) |
| Breaker | 60A double-pole | 240.4 |
| Voltage | 240V single-phase | |
| Conduit (EMT) | 3/4" EMT | Chapter 9 Table 4 |
| GFCI | Required (GFCI breaker or device) | 210.8(A) |
| Max distance (3% VD) | 153 ft at 240V copper | 210.19(A) Note 4 |
100A subpanel (1BR+ ADU)
| Component | Specification | NEC basis |
|---|---|---|
| Wire (copper) | 3 AWG THHN | Table 310.16, 110.14(C) |
| Wire (aluminum alt.) | 1 AWG THHN | Table 310.16, 110.14(C) |
| Breaker | 100A double-pole | 240.4 |
| Voltage | 240V single-phase | |
| Conduit (EMT) | 1" EMT | Chapter 9 Table 4 |
| GFCI | Required (GFCI breaker or device) | 210.8(A) |
| Max distance (3% VD) | 184 ft at 240V copper | 210.19(A) Note 4 |
Installation notes
This project requires GFCI protection per NEC 210.8(A). The simplest approach is a GFCI breaker at the panel, which protects the entire circuit. For 240V circuits, use a 2-pole GFCI breaker sized to match the circuit. GFCI breakers cost $40-80 depending on amperage.
For the wire run, you have two options: NM-B cable (Romex) for interior runs through framing, or individual THHN conductors in conduit for exposed runs, outdoor installations, or runs through unfinished spaces. NM-B is faster to install but cannot be used outdoors or in conduit. For conduit, use EMT (metallic) or PVC Schedule 40.
Run length matters: every foot of wire adds voltage drop, reducing power to your equipment. The table below shows the exact voltage drop at common distances. If your run exceeds the 3% threshold, upsize one gauge.
Voltage drop by distance
Percentage voltage drop at common run lengths. NEC recommends 3% maximum for branch circuits and 5% for combined feeder plus branch.
| Distance | 6 AWG Co | 4 AWG Al | 4 AWG Co |
|---|---|---|---|
| 25 ft | 0.5% | 0.5% | 0.3% |
| 50 ft | 1.0% | 1.0% | 0.6% |
| 75 ft | 1.5% | 1.5% | 0.9% |
| 100 ft | 2.0% | 2.0% | 1.2% |
| 150 ft | 3.0% | 3.0% | 1.9% |
| 200 ft | 3.9% | 4.1% | 2.5% |
Common products for 6 AWG Copper circuits
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Related wire data
Detailed ampacity: 6 AWG copper, 4 AWG aluminum. Wire size lookup: 60A circuit. Calculators: voltage drop · panel load calculator.
Inspection preparation
Before your rough-in inspection, verify these frequently-checked items:
| Check | NEC Ref | Common Fail |
|---|---|---|
| Cable secured within 12 inches of box | NEC 334.30(A) | NM cable not stapled close enough to box |
| Proper wire gauge for circuit amperage | NEC 240.4(D) | 14 AWG on 20A circuit or 12 AWG on 30A circuit |
| Ground wire continuous and properly bonded | NEC 250.148 | EGC not connected in box or spliced incorrectly |
| No NM cable in wet/damp locations | NEC 334.12(B) | Romex used in exterior, underground, or damp location |
| Box fill calculations | NEC 314.16 | Too many conductors in box |
See the full inspection checklist tool for all 19 items with progress tracking.
Frequently asked questions
What wire size do I need for adu / in-law suite wiring?
Use 6 AWG copper or 4 AWG aluminum on a 60A breaker at 240V. This is based on NEC 2023 Table 310.16 ampacity with 110.14(C) termination limits and 125% continuous load sizing per 210.19(A)(1).
Does adu / in-law suite wiring require GFCI?
Yes. GFCI protection is required per NEC 210.8(A).
NEC 2023 references verified April 2026