A "CFGI breaker" (Combination Fault and Ground Interrupter) is the industry's colloquial term for a Dual Function (DF) circuit breaker that provides both Combination Arc-Fault (AFCI) and Ground-Fault (GFCI) protection in a single module. For a standard 120V/15A residential branch circuit, you need a 15A, 120/240V AC rated DF breaker with a 10,000 AIC interrupting capacity. These devices are mandated by NEC 210.12 and 210.8 for most living spaces, kitchens, and laundry areas to protect against both parallel/series arcing and lethal ground faults.
Decoding the CFGI Breaker Rating Table
Unlike standard thermal-magnetic breakers, a CFGI breaker contains an internal printed circuit board (PCB) and a trip solenoid. When selecting a unit, you must evaluate three distinct ratings. The table below breaks down the parameters and explicitly identifies which rating column governs your specific load.
| Parameter | Standard 15A/20A Residential | 30A Appliance / RV | Which Rating Governs the Load? |
|---|---|---|---|
| Trip Unit / Coil Voltage | 120V AC (via pigtail/line) | 120V/240V AC | Governs the control circuit. The internal logic board and trip coil require this specific voltage to power the microprocessor and fire the solenoid. |
| Continuous Contact Rating | 15A or 20A at 60°C/75°C | 30A at 75°C | Governs the steady-state load. Dictates the maximum continuous wire ampacity and the physical thermal limit of the main current-carrying contacts. |
| Breaking Capacity (AIC) | 10,000A (Standard) | 10,000A to 22,000A | Governs fault survivability. Must exceed the available short-circuit fault current calculated at the panel bus bars. |
Load Selection Decision Path
A frequent mistake is applying a standard CFGI breaker to high-inrush loads without checking the magnetic trip threshold. Use this decision-tree-table to select the correct breaker profile based on your load type.
| Load Type | Examples | CFGI Breaker Sizing Rule | Trip Curve Requirement |
|---|---|---|---|
| Resistive | Baseboard heaters, toasters | Size at 125% of continuous load | Standard thermal-magnetic (Curve C equivalent) |
| Inductive | Transformers, LED drivers | Size at 125% load; watch for inrush | Standard, but ensure AFCI algorithm doesn't nuisance trip on switching transients |
| Motor (Fractional HP) | Garage door, disposal | Size at 250% of FLA (NEC 430.52) | High magnetic trip threshold (Curve D or HACR rated) to survive motor starting inrush |
Wiring the Contacts vs. the Control Coil (Pigtail)
Wiring a Dual Function breaker requires understanding the difference between the high-current contact side and the low-current control/coil side.
The Contact Side (Line and Load)
The main current-carrying contacts consist of the bus stab clip (Line/Source) and the screw terminal (Load/Branch).
- Line Side: Slides directly onto the panel's hot bus bar. This feeds power to both the branch circuit and the breaker's internal logic board.
- Load Side: The black (or red) branch circuit hot wire terminates here. Torque the screw to the manufacturer's spec (typically 35-45 in-lbs for 14-10 AWG copper) to prevent contact resistance heating.
The Coil / Control Side (Neutral and Pigtail)
The electronic trip unit requires a 120V reference to power its microprocessor and the internal trip solenoid (coil).
- Load Neutral: The white wire from your branch circuit connects to the breaker's neutral terminal. This allows the GFCI sensor to monitor the imbalance between the hot and neutral currents.
- The Pigtail (Coil Power): The white coiled pigtail must connect directly to the panel's neutral bar. This completes the 120V control circuit for the internal logic board and trip coil.
Technical Note on DC Flyback: While CFGI breakers are strictly AC devices, if you are ever designing custom protection relays or wiring internal trip solenoid coils in a DC control panel, you must install a flyback diode across the coil. When a DC coil de-energizes, the collapsing magnetic field generates a massive reverse voltage spike that will destroy the driver transistor without a flyback diode to dissipate the energy.
Testing Dead vs. Live and the Fuse vs. Breaker Curve
Proper diagnostics require knowing how to test the breaker in both de-energized and energized states.
How to Test It Dead
With the main breaker off and the panel verified dead:
- Continuity Test: Set your multimeter to continuity. Place one probe on the bus stab clip and the other on the load screw terminal. With the breaker handle ON, you should read < 1 ohm. With the handle OFF, it should read OL (open line).
- Insulation Resistance (Megger): For suspected internal arc tracking, a 1000V megohmmeter test between the load terminal and the breaker casing should read >100 MΩ. (Note: Disconnect the pigtail and neutral wire before meggering to avoid frying the internal PCB).
How to Test It Live
- Push-to-Test: Press the physical "Test" button on the breaker face. This shunts a small resistor across the GFCI sensor and injects a simulated arc signature for the AFCI logic. The breaker must trip immediately.
- Voltage Drop: With the circuit under a steady 15A load, measure the AC voltage between the bus bar and the load terminal. A drop greater than 50mV indicates pitted or degraded internal main contacts.
Fuses vs. Breakers: The Time-Current Curve (TCC)
Never treat a fuse and a breaker as interchangeable without consulting the time-current curve (TCC). A 20A dual-element time-delay fuse might hold 40A for 10 seconds to allow a motor to start. A standard 20A CFGI breaker’s thermal element might trip in 3 seconds at that exact same current. Swapping a fuse for a breaker (or vice versa) without verifying the TCC overlap will result in either constant nuisance tripping or, worse, unprotected wire melting during a sustained overload.
When to Repair vs. Replace
Always replace. Molded case CFGI breakers are sealed, factory-calibrated electromechanical assemblies. If the internal trip coil fails, the GFCI sensor drifts, or the main contacts pit, the unit is unrepairable in the field. Attempting to open the molded case destroys the arc chute integrity and voids the UL listing.
CFGI Breaker FAQ
Why does my CFGI breaker keep tripping when I plug in a vacuum?
Vacuums and older power tools use universal motors with brushed commutators. These brushes create intentional, continuous micro-arcing during normal operation. Early generation AFCI/CFGI breakers could not distinguish between normal brush arcing and a dangerous parallel arc fault. If this happens, check the breaker's manufacturing date. Modern units (post-2020) utilize advanced digital signal processing (DSP) algorithms to filter out brush noise. If it's a new breaker, the vacuum's power cord may actually have internal damage causing a real fault.
Can I use a CFGI breaker on a multi-wire branch circuit (MWBC)?
Yes, but you must use a 2-pole Dual Function breaker specifically designed for MWBCs, or two single-pole breakers with an approved handle tie and a shared neutral pigtail configuration (if the manufacturer explicitly supports it). A standard single-pole CFGI breaker will trip immediately on an MWBC because the shared neutral carries the unbalanced current from the opposite phase, which the breaker's GFCI logic will interpret as a ground fault leaking to earth.
How do I know if the GFCI or AFCI side of the CFGI breaker tripped?
Most modern Dual Function breakers feature an LED diagnostic indicator or a specific trip-flag sequence. For example, on many Eaton and Square D models, if the breaker trips and the LED blinks in a specific pattern (e.g., one flash for AFCI, two flashes for GFCI, or a solid light for a thermal overload), you can read the code. Consult the label printed directly on the breaker handle or the manufacturer's diagnostic chart to decode the exact fault type.
Do I still need GFCI receptacles if I have a CFGI breaker?
No. The NEC allows GFCI protection to be provided at the breaker, the receptacle, or anywhere in between. Installing a CFGI breaker at the panel satisfies the GFCI requirement for the entire branch circuit. You can (and should) install standard, non-GFCI receptacles on that circuit to avoid redundant tripping points and save money, unless local AHJ amendments specifically require point-of-use receptacles for easy resetting.
