How to Wire a 20A – 125V Outlet – NEMA 5-20 Receptacle

Electrical Technology

How to Install a Standard 20A – 125V Receptacle (NEMA 5-20) with Breaker and GFCI Protection

A 20A – 120V outlet receptacle (commonly known as a NEMA 5-20R) is a type of electrical outlet designed to supply 120 volts AC supply with a maximum current capacity of 20 amperes. It is used for power-hungry devices and equipment such as air conditioners, heavy-duty power tools, and kitchen appliances connected to dedicated 20A circuits that require more current than a standard 15A outlet on a 120V supply.

The ordinary 20A-120V (NEMA 5-20) outlet is identified by one vertical and one laying “T-shape” slot for the hot and neutral prongs, and a center-top grounding pin in “U shape”. This type of outlet is installed on circuits protected by a single-pole 240V, 20-amp breaker or GFCI. A #12AWG for 3 wire configuration including the EGC is used to wire a 20A-120V outlet.

The NEMA 5-20 is a 2-pole, 3-wire receptacle designed to handle a non-continuous load of up to 20 amps at 120 volts, providing a maximum power capacity of 2,400 watts on a single-phase circuit. For continuous loads, it can safely handle up to 16 amps at 120 volts, equivalent to 1,920 watts.

In the following wiring tutorial, we will demonstrate how to wire a NEMA 5-20 receptacle using both standard and GFCI breakers. The wiring diagrams also show the appropriate breaker ratings and wire sizes for a 20-amp receptacle in both continuous and non-continuous load applications.

Table of Contents

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The NEMA 5-20 Outlets and Receptacles

The NEMA 5-20R is a 20A, 125V grounded receptacle designed for use with NEMA 5-20P or 5-15P plugs. As the name suggests, the “20” in 5-20R indicates the maximum current rating in amperes, while the “R” stands for “Receptacle” (outlet). Similarly, the “P” in NEMA 5-20P denotes “Plug,” with “20” representing its maximum current capacity in amperes.

The 20A, 125V duplex receptacle features a 2-pole, 3-wire configuration. It includes two slots i.e. the narrower slot for the hot wire and a wider, T-shaped slot for the neutral along with a round or U-shaped hole for the equipment grounding conductor (EGC). This receptacle type is commonly used in the U.S., Canada, and other NEC-compliant regions to power high-demand 125V, 20A circuits found in garages, kitchens, and laundry areas.

Good to Know:

✅ 20A – 120V (NEMA 5-20) Outlet: Accepts both 15A and 20A plugs at 120V i.e. NEMA 5-15P and NEMA 5-20P. In other words, a standard 20-amp outlet accept both standard 15-amp plugs (NEMA 5-15P) and 20-amp plugs (NEMA 5-20P).
❌ 15A – 120V (NEMA 5-15) Outlet: Only Accepts 15A – 120V plug i.e. NEMA 5-15P .i.e. a 20A plug cannot be plugged into a 15A outlet.

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Terminals

There are three terminals in a NEMA 5-20R outlet in accordance with UL/CSA.

Narrow / Shorter Terminal (I) on the Right Side: Brass Screw for Hot – Connects to the Black Wire
T-Shaped Terminal (⊣) on the Left Side: Silver Screw for Neutral – Connects to the White Wire
U Shaped “G” Terminal (Green Screw): For equipment grounding conductor (EGC – ⏚) – Bare or Green Wire.

Electrical Ratings & Specifications

NEMA: 5-20R – Straight-Blade, Duplex Receptacle
Poles: 2-Poles, 3 Wires Grounding
Voltage: 125V Single-Phase AC Supply – 60 Hz
Current: 20A -16A
Breaker / GFCI: 20A – 1P
Wattage: 2,400 W
Wire Size: #12AWG Copper
Grade & Material: Residential & Commercial Grade – Temper-resistant (TR) – Thermoplastic Composite
Termination: Quick-wire, Push-In & Side Wired
Mounting: Flush / Screw Mounting
Wiring: Hardwired / Dedicated Circuit

Wiring NEMA 5-20R Outlet

Wiring 20A – 120V Outlet using 1-P Breaker

The following wiring diagram shows the wiring connections of the 20A, 125V outlet (NEMA 5-20R) to a single-pole, 20A breaker in a 120/240V main panel as follows:

The ground (bare or green) wire is connected to the centered, round/U-shaped “G” terminal – green screw.
The hot (black) wire is connected to the shorter/narrow slot terminal – brass screw.
the neutral (white) wire is connected to the T-shaped slot terminal – silver screw

For this circuit, we have used #12 AWG copper wire which is the right size for a 20A circuit and the corresponding NEMA 5-20R outlet.

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During installation, strip the insulation from the conductors according to the connection type:

Side wire: 3/4″ (19 mm or 1.9 cm)
Back wire: 1/2″ (12.7 mm or 1.27 cm)

In addition, tighten all terminal screws to approximately 14-18 in-lbs (1.6-2 N·m) of torque.

Wiring a 15A – 120V Switched Outlet

The ON/OFF operation of a 15A, 120V outlet can be controlled by wiring a single-pole, single-throw (SPST) 20A switch as follows:

Connect the hot (black) wire from the single-pole, 20A, 120V breaker to the line terminal (hot) of the SPST switch.
Connect the outgoing hot wire from the switch to the brass (hot) terminal of the outlet.
Connect the neutral (white) and ground (bare or green) wires to the outlet in the same manner as in a standard outlet wiring configuration.

This way, the ON/OFF operation of the 20A – 120V outlet can be controlled using a switch. When the switch is ON, the outlet will be energized (operational), and when the switch is OFF, the outlet will be de-energized (off).

If the breakaway fin tab between the brass terminals of the outlet remains intact, both receptacles will be controlled simultaneously by the switch for ON/OFF operation. However, if the tab between the hot terminals is removed, only the upper receptacle of the duplex outlet will be controlled by the switch, while the lower receptacle will remain continuously energized regardless of the switch position.

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Pro Tip:

It is good to know that the brass screws (hot terminals) on a duplex receptacle are electrically bonded to each other through a breakaway fin (tab). Therefore, connecting one brass screw to the hot wire will also supply power to the second brass screw. In some cases, this breakaway fin tab between the two brass screws (hot terminals) may be removed to split the outlet for specific applications. This configuration is commonly shown in wiring diagrams for various receptacle installations and specialized setups.

Wiring 15A – 120V Receptacle with GFCI

As per NEC NEC 210.8, GFCI protection is required for receptacles installed in garages, basements, outdoors, laundry areas, and other wet or damp locations. NEC 210.8(A)(1) through (A)(11) mandates that all outdoor receptacles must be installed downstream of GFCI protection, in accordance with Articles 426.28 and 427.22.

When installing a 20A, 120V outlet in any location where GFCI protection is required by code, you can meet the requirement in one of two ways as follows:

Installing a 20A-120V GFCI Outlet

In this method, the wiring procedure remains the same, but a 20A, 120V GFCI duplex outlet is installed instead of a standard 20A, 120V receptacle. The wiring configuration for this setup is illustrated in the diagram below.

Although this method requires installing a GFCI outlet, it helps save space in the main panel because there is no need to purchase or install a separate GFCI circuit breaker.

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Good to Know: At the moment, only 15A and 20A GFCI receptacles rated for 120V are available, (in NEMA 5-15 and NEMA 5-20 configurations). For 240V outlets, GFCI protection must be provided through GFCI circuit breakers, as 240V GFCI receptacles are not manufactured.

Wiring a 15A-120V Outlet with a GFCI Breaker

If a GFCI outlet is not feasible, replace the standard 20A, 120V breaker with a 1-pole, 20A, 120V GFCI circuit breaker. The existing wiring remains the same, as shown in the given wiring diagram.

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

FAQs

How Many Amps Can a 20A – 120V Outlet Handle Safely?

A NEMA 5-20 outlet is designed to handle up to 20 amperes of non-continues current at 125V. For continuous loads (lasting 3 hours or more), the NEC recommends using up to 80% of the outlet rating, which equals 16A.

Good to Know:

These guidelines are based on NEC Articles 210.19(A), 210.20(A), 215.2(A), 215.3, and 230.42(A), which require branch circuits and feeders to be sized based on the continuous and non-continuous load conditions.

How Many Watts Can a 20A – 120V Receptacle Hold?

At 120 volts, a 20A outlet can handle up to 2,400 watts (20A × 120V). For continuous loads (3 hours or more), the NEC recommends using only 80% of the rated capacity, which equals 1,920 watts.

Which Breaker Size is Suitable for a 20A – 120V Receptacle?

A single-pole, 120V – 20A is the suitable sized circuit breaker for protecting a 20A, 120V outlet (NEMA 5-20) circuit.

What is the Correct Wire Size and Cable Type to Use with a 20A – 120V Outlet?

According to NEC Table 310.16, Table 210.24(1), and NEC 240.4(D)(6), the appropriate wire size for use with a 20A outlet and circuit breaker is 12 AWG copper. Likewise, for a 20A circuit, the equipment grounding conductor (EGC) should also be #12 AWG copper, as specified in NEC Table 250.122.

You may use the cable type of 12/2 NM-B (Romex) or 12AWG THHN/MC cable, depending on the installation environment for 20A branch circuits.

In short, a 20-amp circuit should use #12 AWG copper or #10 AWG aluminum (minimum) for safe operation as per NEC.

Good to Know: Aluminum conductors are not recommended for 20A branch circuits.

Can I Use Smaller Size AWG than 12 AWG with a 20A Outlet?

No. Using smaller wire, such as 14 AWG, is unsafe and violates the NEC. Only 12 AWG or larger conductors should be used on 20A circuits.

Can I Use a 20A Outlet on a 15A Circuit Breaker and Vice Versa?

No. Installing a 20A outlet on a 15A breaker is not allowed because the outlet could allow devices to draw more current than the circuit is rated for. However, using a 15A outlet on a 20A breaker is generally permitted, as long as multiple outlets are on the same branch circuit.

Can I Use a 20A Outlet on a 15A Circuit and Vice Versa?

A 20A outlet on 15A circuit is not allowed to use as it may lead to overloading and violates NEC. However, a 15A outlet on 20A circuit can be used, as long as the total load doesn’t exceed 15A.

Can a 15A Device be Plugged into a 20A Outlet?

Yes. A 15A plug can fit into a 20A outlet because of the design of the NEMA 5-20R receptacle, which accepts both 15A and 20A plugs. However, a 20A plug cannot fit into a 15A outlet.

Can a 20A Device be Plugged into a 15A Outlet?

No. A 20A plug has a different prong configuration that won’t fit into a 15A outlet, preventing unsafe connections.

Should I Use a GFCI or Standard Breaker for a 20A Outlet?

Use a GFCI outlet or a GFCI circuit breaker if the receptacle is installed in a location that requires ground-fault protection, such as bathrooms, kitchens, garages, basements, outdoor areas, and laundry rooms. For other areas, a standard breaker is sufficient.

Can You Install a NEMA 5-20R in a 240V AC Circuit?

No. A NEMA 5-20R receptacle is rated for 120 volts only. Installing a 120V device on a 240V circuit is unsafe and violates electrical codes. Use a NEMA 6-20R for 240V applications instead.

What is the Recommended Height for Ordinary Outlet?

According to common practice and NEC recommendations, the standard height for general-use outlets is 12 to 18 inches (30 to 45 cm) from the floor to the center of the receptacle box. Specific applications (such as countertops or garages) may vary.

For example, the height may be up to 42 inches (about 107 cm) above the floor or 18 inches above the countertop surface when installing an outlet in areas such as kitchens, countertops, or bathrooms.

Similarly, in basements, garages, or workshops, outlets are typically installed at a height of about 4 feet (48 inches or 1.2 meters) above the floor.

Instructions, Precautions & Codes

It is permissible to use 15A receptacles on a 20A circuit if there are two or more receptacles (such as duplex outlets) connected on the same branch circuit. In simple terms, a 15A device can safely be plugged into a 20A outlet.
it is against the code to connect a 20A load to a 15A receptacle. A 20A plug will not fit into a 15A outlet, and forcing it is dangerous.
A standard 20A outlet (NEMA 5-20R) accepts both 15A and 20A plugs, but the reverse is not true i.e. a 15A outlet cannot accept a 20A plug.
According to the NEC Table – 310.16 , Table 210.24.(1) and NEC 240.4(D)(6), the correct Breaker and Wire size for a 20-Amp, 120V (5-20R) outlet is #12 AWG copper or #10 AWG Aluminum.
Use #12/2 cable (hot, neutral, and ground) for wiring a 20A-120V breaker and outlet.
For longer runs exceeding 50 feet (15.25 meters), a larger wire gauge should be used to compensate for voltage drop.
A 20A outlet can supply up to a 16A continuous load and a maximum of 20A non-continuous load, as per NEC 210.19(A), 215.2, and 230.42(A).
It is not permitted to use a 20A receptacle on a 15A breaker, or to use undersized conductors (e.g., 14 AWG or 16 AWG) on a 20A circuit. Use the correct size of 12AWG for 20A outlets and breakers.
According to NEC 310.16, an additional 20% ampacity should be considered for every 100 feet (30.5 meters) of wire length to offset voltage drop. For long-distance runs and ambient temperature adjustments, refer to NEC 110.14(C), 310.15(B)(2), 310.16, and 240.4(A).
A 20A, 120V outlet must be installed only on a 20A circuit breaker.

Warning

Always turn off the power supply by switching OFF the circuit breaker in the main electrical panel before performing any electrical work.
If you are unsure or inexperienced, it is strongly recommended to contact a licensed electrician to perform the work in accordance with local electrical codes and safety regulations.
The author assumes no responsibility or liability for any losses, injuries, or damages resulting from the use, misuse, or improper application of the information provided. Please be safe because playing with electricity is extremely dangerous.