Wire sizing is about choosing a conductor that carries the current safely without overheating or losing too much voltage. Three ideas cover the basics.
1. Gauge (AWG)
Wire size is given in American Wire Gauge, where a smaller number means a thicker wire. Thicker wire has less resistance and carries more current.
2. Ampacity
Each wire size has an ampacity — the current it can safely carry continuously. The breaker protecting a circuit is matched to the wire so the wire never carries more than it can handle:
| Wire (copper) | Typical circuit |
|---|---|
| 14 AWG | 15 A |
| 12 AWG | 20 A |
| 10 AWG | 30 A |
3. Voltage drop
Over long distances, resistance causes voltage to “drop” along the wire, leaving less at the load (dim lights, weak motors). For long runs you increase the wire size beyond what ampacity alone requires — commonly considered once a run passes ~50 feet.
Frequently asked questions
Does a smaller gauge number mean thicker wire? Yes — lower AWG is thicker.
What is ampacity? The current a wire can safely carry continuously.
Why upsize wire for long runs? To limit voltage drop so the load gets enough voltage.