Module 4 · 45 minutes
Overcurrent protection and conductor sizing
Connect conductor ampacity, terminal limits, load behavior, and protective devices.
Learning objectives
By the end, you should be able to:
- Distinguish overloads, short circuits, and ground faults
- Explain how overcurrent protection relates to conductor ampacity
- Identify the checks required before selecting a conductor
Foundation
Breakers and fuses protect conductors and equipment from excessive current under defined conditions. An overload is different from a short circuit or ground fault, even though each can cause an overcurrent protective device to open.
Conductor sizing may require checking:
- Load calculation
- Continuous-load treatment
- Conductor material and insulation
- Wiring method
- Terminal temperature limitations
- Ambient-temperature correction
- Adjustment for the number of current-carrying conductors
- Equipment and manufacturer requirements
Familiar starting points
| Typical branch circuit | Common copper conductor |
|---|---|
| 15 A | #14 AWG |
| 20 A | #12 AWG |
| 30 A | #10 AWG |
These familiar pairings are not substitutes for checking the complete installation and the currently adopted code.
Field check
List every fact you would need before selecting conductors for a load expected to operate for three hours or more.