Home Electrical Wiring Guide: Gauge, Amperage, and Circuit Basics

Wire Gauge and Amperage Basics

AWG (American Wire Gauge) — counterintuitively, lower numbers = thicker wire = higher ampacity:

14 AWG: 15-amp circuits — general lighting, outlet circuits
12 AWG: 20-amp circuits — kitchen, bathroom, garage outlets
10 AWG: 30-amp circuits — electric dryers, some AC units
8 AWG: 40-amp circuits — electric ranges
6 AWG: 55-amp circuits — large AC units, subpanels

Never use undersized wire for a circuit — it's a fire hazard. Using larger wire than required is always safe but wastes money.

GFCI and AFCI Requirements

GFCI (Ground Fault Circuit Interrupter): Required in wet areas — bathrooms, kitchens (within 6 ft of sink), garages, outdoors, crawlspaces. Protects against shock from ground faults.

AFCI (Arc Fault Circuit Interrupter): Required in bedrooms and most living areas by modern NEC code. Detects arcing in wiring that can cause fires. Required for most new circuits in new construction and major renovations.

When to DIY vs. Call an Electrician

DIY-appropriate (with permit where required): Replacing outlets and switches, installing ceiling fans (existing wiring), replacing light fixtures.

Call an electrician: Panel work (dangerous, permit required), running new circuits, service entrance upgrade, anything involving aluminum wiring (requires special anti-oxidant compound and aluminum-rated devices).

Frequently Asked Questions

Do I need a permit to add an outlet?

In most jurisdictions, yes — any new circuit or significant wiring change requires a permit. Replacing an existing outlet on an existing circuit often doesn't. Permit requirements vary by municipality; check with your local building department before starting work.

What is knob-and-tube wiring and should I replace it?

Knob-and-tube (K&T) was standard wiring from approximately 1880–1940. It has no ground wire, isn't rated for modern loads, and is incompatible with insulation (fire risk if insulation touches the wires). Most insurers surcharge or refuse to cover homes with active K&T. Replacement is expensive ($5,000–20,000+) but often necessary.