Branch Circuits & Conductor Requirements
Branch circuit sizing, conductor types, NMD90 cable, ampacity ratings, overcurrent protection, and voltage drop calculations.
- Match conductor sizes to branch circuit ampere ratings
- State the maximum overcurrent protection for 14 AWG and 12 AWG conductors
- Identify NMD90 as the standard residential branch circuit cable in Canada
- Explain voltage drop limits for branch circuits and feeders
- Describe the rules for using aluminum conductors in residential installations
- State the minimum insulation rating for residential conductors
Lección 1
Branch Circuit Sizing & Overcurrent Protection
Matching Conductors to Breakers
The OESC requires that conductors be sized to safely carry the load and that overcurrent devices (breakers or fuses) protect the conductor from overheating. The key conductor-to-breaker relationships for residential work are:
15-Ampere Circuits
The minimum conductor size for a 15-ampere branch circuit is 14 AWG copper. This is the most common branch circuit in residential wiring, used for general-purpose receptacles and lighting in bedrooms, living rooms, and hallways.
20-Ampere Circuits
The minimum conductor size for a 20-ampere branch circuit is 12 AWG copper. These circuits are used for kitchen counter receptacles, bathroom receptacles, laundry receptacles, and other higher-demand locations.
Overcurrent Protection Limits
The maximum rating of an overcurrent device for a 14 AWG copper conductor is 15 amperes. You cannot install a 14 AWG conductor on a 20A breaker - the breaker would allow current that could overheat the smaller conductor.
| Conductor Size | Maximum Overcurrent Device | Common Use |
|---|---|---|
| 14 AWG copper | 15A | General lighting and receptacles |
| 12 AWG copper | 20A | Kitchen, bathroom, laundry |
| 10 AWG copper | 30A | Dryer, water heater |
| 8 AWG copper | 40A | Range, cooktop |
| 6 AWG copper | 50A - 60A | Large range, EV charger |
Common Exam Trap
The exam may ask for the minimum conductor size or the maximum overcurrent protection. 14 AWG = 15A maximum. 12 AWG = 20A maximum. Never exceed these ratings.
14 AWG copper is the minimum for a 15A branch circuit with a maximum 15A overcurrent device. 12 AWG copper is the minimum for a 20A branch circuit. Always match conductor size to breaker rating.