How to Wire a 50A – 125V – NEMA 5-50 Receptacle

Electrical Technology

How to Install a 50A -125V Receptacle (NEMA 5-50R) with GFCI / Breaker

The NEMA 5-50R is a 125 V, 50 A receptacle, once used for heavy-duty 120V equipment but now nearly obsolete. It’s not standard or recommended for new residential or commercial installations under modern NEC practices. Most 50A applications today use 240V receptacles like NEMA 6-50R or 14-50R instead.

NEMA 5-50R receptacles were used for large 120V appliances (e.g., heavy-duty commercial equipment, welders, or industrial vacuum cleaners), some RV park pedestals (older installations) and commercial or shop environments which requires high current at 120V. Nowadays, NEMA 5-50R are rare and uncommon (now mostly obsolete) in new installations.

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The NEMA 5-50 Receptacle

A NEMA 5-50 is a 125-volt, 50-amp (2-pole, 3-wire) grounding receptacle, used for welders and generators. The “5” in the designation indicates a 3-wire, 125-volt configuration (hot, neutral, and ground), while the “50” specifies the 50-amp rating.

A NEMA 5-50 receptacle is not compatible with other NEMA configurations, such as a NEMA 14-50 or NEMA 6-50, which operates at 240V.

Similarly, NEMA 5-50R are not used in residential setting as there’s no household equipment designed for NEMA 5-50.

Terminals

There are three terminals in a NEMA 5-50R receptacle as follows:

(I) = Narrow Vertical Terminal (Brass Screw) on the Left Side: Connects to the Hot – Black Wire
(|) Longer Vertical Terminal (Silver Screw) on the Right Side: Connects to the Neutral – White Wire
(U) Shaped “G” Terminal (Green Screw): Connects to the Ground (EGC) – Bare or Green Wire

Electrical Ratings & Specifications

NEMA: 5-50R – Straight-Blade Receptacle
Poles: 2-Poles, 3 Wires Grounding
Voltage: 125V Single-Phase AC Supply – 60 Hz
Current: 50A – 40A
Breaker / GFCI: 50A
Wattage: 6,000 W
Wire Size: #6 AWG Copper
Grade & Material: Commercial Grade – Thermoplastic/Composite
Mounting: Flush / Screw Mounting
Outdoor Box: 2-gang outdoor box – NEMA 3R rainproof enclosure
Wiring: Hardwired / Dedicated Circuit

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Wiring NEMA 5-50R Receptacle

Wiring 50A-120V Outlet using 1-P Breaker / GFCI

The following wiring diagram illustrates the wiring connections of a 50A, 125V outlet (NEMA 5-50R) to a single-pole, 120V – 50A breaker or GFCI in a 120/240V main panel, as shown below:

To wire a NEMA 5-50R, follow the following simple steps:

Strip 1 inch (25mm) of insulation from the conductors.
Connect the ground (bare or green) wire to the green screw – the centered, round or U-shaped “G” terminal.
Connect the hot (black) wire to the brass screw – the shorter or narrow vertical slot terminal.
Connect the neutral (white) wire to the silver screw – the longer vertical terminal.
Once fixed in the slots, tighten all terminal screws to approximately 30 lb-in (3.4 N·m) of torque.

For this circuit, use #6 AWG copper wire, which is the correct size for a 50A circuit and the associated NEMA 5-50R outlet.

For outdoor installations, use a NEMA 3R weatherproof 2-gang enclosure for NEMA 5-50 to protect the receptacle from moisture and environmental exposure.

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In the case of a 50A outlet used for RV park pedestals (older installations) or outdoor wiring where GFCI protection is required, simply replace the single-pole breaker with a single-pole, 50A-125V GFCI breaker. While replacing the standard breaker with GFCI, don’t forget to connect the built-in pigtail (white wire) from the GFCI to the neutral busbar in the main panel.

Good to Know:

According to NEC 210.8, GFCI protection is required for receptacles installed in garages, basements, outdoors, laundry areas, and other wet or damp locations.

Specifically, 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.

FAQs

Are NEMA 5-50R Receptacles Still Used Today?

They are very rare and seldom used in modern installations. Most new 50A outlets are 240V, i.e. NEMA 6-50R (for welders) or NEMA 14-50R (for ranges, EV chargers, RVs). A 50A, 125V circuit is inefficient and unusual and only few appliances require that much current at 120V.

Is It Allowed to Install NEMA 5-50R in New Installations?

The NEC does not prohibit NEMA 5-50 receptacles outright i.e. any listed and labeled device can be used if the load requires it. However, it’s not standard practice for residential or commercial wiring because:

No common household appliance requires 50 A @ 120V.
Most 50A branch circuits are 240V, not 120V.

Hence, inspectors may question or reject a 5-50R unless it’s clearly required by manufacturer specs.

How Many Amps Can a 50A – 125V Receptacle Handle Safely?

A 50-amp outlet is designed to handle up to 50 amps continuously under normal conditions.
However, per NEC 210.19(A)(1) and NEC 210.20(A), continuous loads (lasting more than 3 hours) should not exceed 80% of the circuit rating.

Safe continuous current: 50A × 0.8 = 40A

So, a 50A-120V outlet can safely handle 40 amps continuously and up to 50 amps for non-continuous loads.

How Many Watts Can a 50A – 125V Receptacle Hold?

To find wattage capacity:

P = V × I

120V × 50A = 6,000W

The maximum (non-continuous) power a 50A -120V outlet can handle is 6,000 watts (6 kW).

Safe Continuous Power (80% rule):

120V × 40A = 4,800W

So, it can safely deliver 4.8 kW continuously or up to 6 kW total.

Which Breaker Size is Suitable for a 50A – 125V Receptacle?

Based on the breaker sizing and selection, 1-Pole, 120V – 50A thermal-magnetic circuit breaker (or GFCI if required by NEC 210.8 for outdoor, garage, or wet locations) is required for a 120V, 50A (NEMA 5-50) receptacle.

What is the Correct Wire Size and Cable Type to Use with a 50A – 125V Receptacle ?

For a 50A circuit, the minimum required conductor size is #6AWG copper which can safely handle 50 amps per NEC Table 310.16 and Table 210.24(1). Similarly, use #10AWG for 50A circuit as EGC per NEC Table 250.122.

For NEMA 5-50R, you may use NM-B 6/2 for indoor dry locations, UF-B 6/2 for outdoor direct burial and THHN/THWN 6 AWG in conduit.

Instructions, Precautions & Codes

The 5-50R should not be used with single-gang wall boxes. Use a 2-gang outdoor box and NEMA 3R rainproof enclosure, especially for outdoor applications.
According to NEC Table – 310.16, and Table 210.24(1) the correct wire size for a 50A circuit and outlet is #6 AWG copper. Likewise, the appropriate breaker size is a 50A, 120V single-pole breaker (or 50A 1-P, GFCI breaker) when wiring a NEMA 5-50R receptacle, using the same wire size (#6 AWG) copper conductors.
A 50A outlet can supply up to a 40A continuous load and a maximum of 40A non-continuous load, as per NEC 210.19(A), 215.2, and 230.42(A).
Use #10/2 cable (hot, neutral, and ground) for wiring a 50A-120V breaker and outlet.
Use 50A, 120V outlet as a dedicated circuit for single unit.

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.