GFCI & AFCI Protection
Ground fault and arc fault circuit interrupter operation, required locations, trip thresholds, bathroom/outdoor/garage/basement protection.
- Explain the operating principle and trip threshold of GFCI devices
- Identify all OESC-required GFCI locations in dwelling units
- Explain the operating principle and purpose of AFCI devices
- Identify all OESC-required AFCI locations in dwelling units
- Describe the differences between GFCI and AFCI protection
Lección 1
GFCI Operation & Required Locations
How a GFCI Works
A Ground Fault Circuit Interrupter (GFCI) monitors the current flowing on the hot and neutral conductors. Under normal conditions, the current on both conductors is equal. When current leaks to ground through a person or faulty equipment, there is an imbalance between hot and neutral. The GFCI detects this imbalance and trips at 5 milliamperes (mA) - fast enough to prevent electrocution.
The GFCI uses a current transformer (toroid) that wraps around both the hot and neutral conductors. When the magnetic fields are balanced, no signal is produced. When a ground fault creates an imbalance of 5 mA or more, the toroid produces a signal that triggers the trip mechanism.
Exam Tip
A GFCI trips at 5 mA of current imbalance between hot and neutral. It does NOT measure overcurrent or voltage - only the difference between hot and neutral current. This is the most tested GFCI fact.
Types of GFCI Devices
- GFCI receptacle - built into the outlet, protects downstream devices on the "load" terminals
- GFCI breaker - installed in the panel, protects the entire circuit
- Portable GFCI - plug-in device for temporary protection (construction sites)
GFCI Required Locations
The OESC 29th Edition (2024) requires GFCI protection for all 125V receptacles in the following locations:
| Location | Requirement |
|---|---|
| Bathrooms | All receptacles |
| Kitchens | Within 1.5 m of sink |
| Outdoors | All receptacles |
| Garages | All receptacles |
| Unfinished basements | All receptacles |
| Crawl spaces | All receptacles |
| Boat houses | All receptacles |
| Hot tub / pool areas | All receptacles within zone |
A GFCI detects current imbalance between hot and neutral and trips at 5 mA. It protects against electrocution from ground faults. Required locations include bathrooms, kitchens (near sinks), outdoors, garages, and unfinished basements.