How to Wire a GFCI Outlet – Wiring a GFCI Receptacle

Electrical Technology

How to Install a 15A/120V and 20A/120V GFCI Receptacle Outlet

Table of Contents

What is a GFCI?

GFCI (Ground Fault Circuit Interrupter) is a protective device that automatically detects ground faults and leakage currents, providing personal protection against electrocution. As an outlet/receptacle, combo unit, or circuit breaker, a GFCI disconnects the power supply within milliseconds when an electric shock hazard is detected.

According to the NEC (National Electrical Code), GFCIs must be installed in locations where water and electricity are likely to come into contact. These include bathrooms, kitchens, laundry areas, workshops, swimming pools, hot tubs, and other damp or wet environments (e.g., near water pipes). See NEC Code Requirements for GFCI.

GFCI devices are especially important for cord-connected appliances and equipment used outdoors or near water. There are several types of GFCIs, including:

GFCI Outlet (Receptacle)
GFCI Combo (Switch and Outlet)
GFCI Circuit Breaker
Portable GFCI

In today’s wiring tutorial, we will demonstrate how to wire and install a GFCI outlet in residential settings to protect ordinary receptacles, light switches, and other connected devices.

The figure below illustrates what a GFCI is and how to wire it.

Before installation, it is important to understand the difference between a GFCI outlet and a standard (ordinary) receptacle. As shown in the figure above, the Line (Hot/Live/Phase) terminals are connected to the narrow blade, while the Neutral terminals are connected to the wide blade.

In a standard receptacle, there is a breakaway fin between the upper and lower terminals, which allows both outlets to share the same supply connection. This means that connecting the incoming phase and neutral wires to one side will power both outlets.

In contrast, a GFCI outlet has no such breakaway fin. Instead, it is equipped with clearly marked LINE and LOAD terminals. The correct identification of these terminals must be verified by the nameplate data rating printed on the device or in the manufacturer’s user manual.

In the example diagram above, the LOAD terminals are not connected, meaning any downstream outlets, switches, or additional loads are not protected by the GFCI. In this case, only the two outlets built into the GFCI device itself are protected.

Next, let’s see how to wire a GFCI receptacle so that it also provides protection to additional downstream loads.

NEC Requirements of GFCI:

The NEC – 210.8(A)(1) through (A)(11) for dwelling and non-dwelling unites mandates GFCI protection for circuits in bathrooms, garages, kitchens, laundry areas, crawl spaces, unfinished basements, and outdoor areas, as well as for certain appliances like dishwashers or sump pumps. A GFCI breaker ensures compliance for the entire circuit in these areas.
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.

Related Post: How to Wire GFCI Combo Switch and Outlet – GFCI Switch/Outlet Wiring Diagrams

Wiring 15A – 120V GFCI Receptacle Outlet

As shown in the wiring diagram, the line terminals of a 15-amp GFCI receptacle are connected to the 120V supply using #14 AWG wire. The hot wire (black) and the neutral wire (white) from the 15-amp breaker in the 120V/240V main panel are connected to the narrow blade (hot terminal) and the wide blade (neutral terminal) of the GFCI receptacle, respectively.

The ground wire (green or bare copper) is connected to the ground terminal of the outlet. The 15-amp GFCI receptacle typically comes in the NEMA 5-15R configuration.

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This wiring method ensures that the receptacle is GFCI protected. According to the NEC 80% rule, a 15-amp GFCI receptacle can safely supply up to 12 amps for continuous loads and 15 amps for non-continuous loads.

Wiring 20A 120V GFCI Outlet

The wiring method for a 20-amp, 120V GFCI receptacle is the same as for the 15-amp version. The main difference is that the neutral slot is T-shaped on a 20-amp receptacle, whereas it is a straight wide slot on a 15-amp receptacle. This receptacle type is classified as NEMA 5-20R.

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For this circuit, use #12 AWG wire and a 20-amp breaker. As per the NEC continuous load rule, a 20-amp GFCI receptacle can safely supply up to 16 amps for continuous loads and 20 amps for non-continuous loads.

Good to Know: Currently, only 15A and 20A GFCI receptacles rated for 120V are available, commonly in NEMA 5-15 and 5-20 configurations. For 240V circuits, GFCI breakers must be used since 240V GFCI receptacles are not available.

Wiring a GFCI Outlet with a Light Switch

In the first diagram, the single way switch and light bulb is connected to the load terminal of GFCI. This way, the switch and light bulb is GFCI protected.

In the second diagram, the light switch is connected to the line terminals of GFCI. It means, the light switch is not GFCI protected and will operate as a normal circuit.

Wiring a GFCI Outlet with a Ordinary Outlet / Receptacle

Same like above GFCI wiring diagrams, the ordinary outlet is connected to the load terminals of GFCI. So the GFCI outlet and ordinary outlet connected to the load terminals of GFCI is protected from the ground and earth leakage current.

In the following diagram, the normal outlet is connected to the direct line supply i.e. line terminals of GFCI. This way, the ordinary outlet is not GFCI protected.

Related Post: How to Wire Combo Switch and Outlet?

Wiring a GFCI Outlet with Combo Switch – Outlet, Receptacle & Light Switch

In this GFCI outlet wiring and installation diagram, the combo (switch + outlet), SPST (single way) switch and ordinary outlet is connected to the load side of GFCI. It means, all the connected loads to the load terminals of GFCI are protected. The toggle switch in the combo switch outlet controls the first light bulb while the single way switch controls the second bulb. In short, all the loads is GFCI protected.

In the following diagram, the above load mentioned before i.e. components and devices are connected to the line terminals of GFCI i.e. they are connected to the direct main supply. This way, the combo switch – outlet, light switch and ordinary outlet are not GFCI protected.

You can add more loads according to your needs but keep in mind that the maximum allowable number of boxed per circuit breaker is 12 where one circuit consists of all boxes on one circuit breaker. In addition, see the following general rules of thumbs and safety precautions for GFCI installation as well.

Related Post: How to Wire a GFCI Circuit Breaker? 1, 2, 3 & 4 Poles GFCIs Wiring

Rule of Thumbs for GFCI

Only one GFCI/AFCI per circuit. If you increase the limit, it may leads to trip the circuit.
GFCI circuit breaker protects the whole circuit while a GFCI outlet can be installed to protect additional outlets and switches etc.
No need to install an additional GFCI if the circuit is already protected by the GFCI circuit breaker.
For perfect operation of a GFCI, it is must to properly ground the GFCI or it will not trip instantly but will trip before the serious damage and electric shock.
Both 15A and 20A GFCI outlets can be back wired and side-wired.
Torque the screw terminals up to 16 lbf.in (1.8 nm) or refer to the receptacle marking.
No GFCI should be used with some devices like power vented water heater or it will interrupt the proper operation of the circuit.
Both Test and Reset button on a GFCI is for testing purpose only i.e. GFCI must be tested before final operation to make sure it is working properly.
Use #14 AWG for 15A and #12 AWG wires for 20A circuit breakers.
15A and 20A GFCI can be installed on 15-20A and 20A only (not 15 and 30A) circuit breaker respectively.

Precautions:

Switch off the main circuit breaker to make sure the power supply is OFF before wiring a GFCI outlet.
Use the suitable voltage and ampere rating of switch with appropriate wire size and proper size MCB according to the load rating.
Always connect incoming power wires to the LINE terminals and any downstream wires to the LOAD terminals on the GFCI. Incorrect connections (e.g., reversed Line and Load) will prevent proper operation and GFCI protection.
Regular maintenance, check and test is recommended while test the portable GFCI before each operation.
Contact the authorized and licensed electrician for GFCI installation if you are not sure about the wiring diagrams.
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 it’s all about electricity and electricity is too dangerous.

NOTE: For illustration purposes, we have used black for hot, white for neutral, and green for ground conductors. Always follow the local area wiring color codes (e.g., NEC, IEC), or other applicable standards).