How to Wire a Single-Pole GFCI Breaker in a 120/240V Panel

Electrical Technology

How to Install a 1-P, 15A – 120V GFCI Breaker for Branch Circuits

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1-Pole GFCI Breaker

A single-pole GFCI (Ground-Fault Circuit Interrupter) breaker is a protective device designed to provide both overcurrent protection and ground-fault protection for 120V branch circuits. Unlike a standard single-pole breaker, a GFCI breaker continuously monitors the current balance between the hot (ungrounded) conductor and the neutral (grounded) conductor. If an imbalance exceeding 4–6 mA is detected, it indicates current leakage to ground, hence the GFCI breaker trips instantly to reduce the risk of electric shock and fire hazard.

1-pole GFCI breakers are commonly installed in 120/240V split-phase panels to protect circuits supplying receptacles or equipment in wet, damp, or hazardous locations such as bathrooms, kitchens, garages, outdoors, basements, laundry areas, and similar locations mandated by the National Electrical Code (NEC).

A GFCI breaker differs from a standard breaker. It protects one 120V hot conductor (supplied either from Hot 1 or Hot 2) and offer protection against ground faults and overcurrent.

A 1-P GFCI requires a neutral connection to the breaker, that’s why it includes a built-in white pigtail neutral wire which connects to the neutral busbar in the main panel. Similarly, the load side neutral is connected to the GFCI, not to the neutral busbar in the main panel. This way, a GFCI protects the entire branch circuit, not just individual receptacles. In short, a GFCI provides both overcurrent (like ordinary breaker) and ground-fault protection against electric shock hazards.

Characteristics:

Number of Poles: 1-pole – connects to one line (either L1 or L2), i.e. one hot conductor (black or red).
Voltage: Operates on and protects 120V branch circuits. (Line-to-Neutral).
Amperage Rating: Commonly available in 15A, 20A, 25A and 30A.
Wiring: The hot and neutral conductors from the GFCI breaker, along with Ground wire from the ground busbar, connect to the 120V branch-circuit load. The built-in white pigtail on the GFCI breaker always connects to the neutral busbar.
Operation: Trips when it detects leakage current between Line to Neutral or there is an overload, short circuit, or fault on the single hot (or phase) wire.
Application: As per NEC requirement – mostly used for standard lighting, outlets, receptacles, sockets and small appliances in outdoor and wet locations.

NEC Requirements for GFCI Protection:

NEC 210.8(A) requires GFCI protection for 125/250V, single-phase, 15 and 20-amp receptacles in specified locations including bathrooms, garages, outdoors, basements, kitchens, laundry areas, spas, hot tub and similar spaces.

As per 210.8(A), for dwelling and non-dwelling units, all 120/240V outlets and receptacles installed in the locations specified in 210.8(A)(1) through (A)(11) and supplied by single-phase branch circuits rated 150V or less to ground shall have GFCI protection.

GFCI protection is required for various applications in compliance with the following NEC Articles: 210.8, 406.3, 424.44, 426.28, 427.22, 511.12, 517.17, 517.20, 525.23, 530.44, 547.28, 555.35, 620.6, 625.54, 680.5, 680.21, 680.22, 680.23, 680.27, 680.32, 680.43, 680.44, 680.51 through 680.59, 680.62, and 680.71.

Wiring a Single-Pole GFCI Breaker in a 120/240V Panel

To replace or install a new 1-P GFCI breaker in a 120/240V main panel, follow the following step by step wiring guide.

Turn Off Power: Switch OFF the main breaker supplying the panel. Confirm with a voltage tester that the bus bars are de-energized (except the service lugs prior to the main switch).

Snap the new GFCI breaker firmly onto the panel bus bar (either on L1 or L2). If replacing with a standard breaker, use the exact slot used for the previous circuit breaker.

Identify the following branch circuit conductors:

- Hot conductor (Black or Red)
- Neutral conductor (White)
- Equipment Grounding Conductor (EGC) – Green/Bare conductor as Grounding wire
- GFCI breaker factory-attached pigtail (to be connected to the neutral busbar)

Connect Load Side Conductors as follow:

- Insert the branch-circuit hot wire (black) into the breaker’s LOAD terminal.
- Insert the branch-circuit neutral (white) into the neutral terminal on the GFCI breaker.
- Terminate the breaker’s white pigtail to the neutral bus bar in the panel
- Terminate the bare or green grounding conductor to the grounding bus bar.

Restore Power and Test/Reset the Breaker as follow:
- Replace the panel cover and Turn ON the main breaker as well as newly installed GFCI breaker.
- Press the TEST button on the breaker to verify proper operation. Reset the breaker after testing.

Restore Power and Test/Reset the Breaker as follow:
- Replace the panel cover and Turn ON the main breaker as well as newly installed GFCI breaker.
- Press the TEST button on the breaker to verify proper operation. Reset the breaker after testing.

Good to Know:

For termination, strip about ½” (≈12.7 mm) of insulation from each conductor.
The required tightening torque for conductor termination is 40.7 lbf·in (4.6 N·m) for conductors with cross-sectional areas ranging from 0.006 to 0.03 in² (4 to 20 mm²), or as specified by the panelboard or circuit breaker manufacturer’s markings.
The connection of built-in white pigtail to the neutral busbar in the main panel is mandatory for proper GFCI operation.
Ensure the neutral bus is correctly bonded (in the main panel / service disconnect) or isolated (in the sub-panel) depending on panel type.
A shared neutral is not permitted on GFCI-protected single-pole circuits. In other words, each GFCI breaker must have its own dedicated neutral.
Do not connect a GFCI breaker to a load conductor with a total one-way length exceeding 250 ft (76 m).

In the example wiring diagram, a 15A/120V, 1-P GFCI breaker is wired to protect a 15A – 125V receptacle (NEMA 5-15). As per NEC Table 310.16, the suitable size for a 15A circuit and the associated NEMA 5-15R outlet is #14 AWG. The same wire size i.e. #14AWG should be used for equipment ground conductor (EGC) per NEC Table 250.122.

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How to Wire a Single Pole GFCI Circuit Breaker — Wiring a Single-Pole GFCI Circuit Breaker

Similarly, the following wiring diagram shows a 20A/120V 1-Pole GFCI breaker wired with a 20A – 125V receptacle (NEMA 5-20) outlet.

How to Wire 20A - 120V, 1-Pole GFCI Breaker — Wiring 20A-120V GFCI Breaker

Expect the 15/20A outlets and receptacles, a single-pole GFCI breaker can be wired for different ratings and NEMA outlets used in 120V supply systems such as.

Instructions, Precautions & Codes

As per NEC Table – 310.16, Table – 210.24(1) and NEC 240.4(D)(4), the suitable wire size is 14 AWG copper (or #12 AWG aluminum) to use with a 15A outlet and protected by a 15/120V GFCI/Breaker.
As per NEC Table 250.122, use the same #14 AWG copper for ground (EGC) wire size.
The correct size of breaker is 1-pole, 15A circuit breaker or GFCI for a 15A-125V outlet – NEC 210.21(B)(2).
For a 1-pole, 15A GFCI circuit, you may use NM-B (Romex) for indoor and dry locations, UF-B for outdoor or underground runs, and THHN/THWN conductors when installed in conduit.
A single-pole 15A GFCI/breaker can be used for 12A continuous load (which lasts 3 or more hours) and maximum 15A non-continuous load – 210.19(A), 210.20(A), 215.2(A), 215.3, and 230.42(A).
A 1-pole, 15-amp breaker/GFCI at 120 volt can handle non-continuous load of 1,800 watts (15A × 120V). For continuous use, limit the load to about 1,440 watts (80% of 1,800W).
Do not use 20A outlet on 15A circuit breaker. If more than one receptacle on the same circuit, you may allowed to use 15A outlet on 20A circuit breaker. In other words, It is code to use 15A outlet on 20A breaker (NEC 210.21(B)(2)), but it is not allowed to use 20A outlet on 15A breaker.

Warning:

Make sure to disconnect the power supply by switching OFF the breaker in the main panel before doing any electrical work.
If you are unsure, contact a licensed electrician to do it according to the local area codes.
The author will not be liable for any losses, injuries, or damages from the display or use of this information or if you try any circuit in wrong format. So please! Be careful because electricity is too dangerous.

Resources:

Standard Breakers & GFCI Breakers Wiring Installations

How to Wire a 1-Pole GFCI … You are Here
How to Wire a 2-Pole GFCI
How to Wire a 3-Phase, 3-Pole GFCI
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How to Wire a 2-Pole Breaker
How to Wire a 3-Pole Breaker
How to Wire a Tandem Breaker
How to Wire GFCI Circuit Breakers
How to Wire an AFCI Breaker

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