How to Wire a 30A – 125V – NEMA 5-30 Receptacle

Electrical Technology

How to Install a 30A – 125V Receptacle (NEMA 5-30R) with GFCI / Breaker

A 30A-125V NEMA 5-30 receptacle is a heavy-duty, single-phase grounding electrical outlet designed to supply 120 volts (nominal 125V) with a maximum current rating of 30 amperes. It has three slots (Hot, Neutral & ground) and is used for connecting high-amperage appliances through NEMA 5-30P.

NEMA 5-30R is an older, non-standard type of 30-amp receptacle, rarely used in typical residential and commercial buildings today. In other words, 30A – 125V receptacles are not used with standard household appliances as it’s meant for heavy-duty loads only.

The NEMA 5-30, is a 2P- 3W receptacle used where higher 120V current is required than a typical 15A or 20A outlet can provide. These outlets are used in industrial, commercial, or residential settings such as air compressors, electric heaters, generators and RVs power pedestals rated at 30A – 120V single-phase AC supply.

In the following wiring tutorial, we will show how to wire a NEMA 5-30 receptacle using standard or GFCI breakers with correct breaker and wire sizes for a 30-amp – 120 volt circuits.

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The NEMA 5-30 Receptacle

The NEMA 5-30R is a 30A, 125V grounded receptacle designed for use with NEMA 5-30P plugs. As the name suggests, the “30” in 5-30R indicates the maximum current rating in amperes, while the “R” stands for “Receptacle” (outlet). Similarly, the “P” in NEMA 5-30P denotes “Plug,” with “30” representing its maximum current capacity in amperes.

The 20A, 125V receptacle features a 2-pole, 3-wire configuration. It includes two slots i.e. the narrower slot for the hot wire and a half-T-shaped slot for the neutral along with a round or U-shaped hole for the equipment grounding conductor (EGC). This receptacle type is rarely used to power high-demand 125V, 30A circuits found in industrial and commercial settings.

Terminals

There are three terminals in a NEMA 5-30R receptacle as follows:

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

the NEMA 5-30 and TT-30 receptacles are both rated for 30 amps at 120V, but they are not interchangeable and are designed for very different applications. NEMA 5-30R are straight-blade and used for heavy-duty 120 V equipment (industrial, shop tools, HVAC, etc. while TT-30R are angled blade (designed to meet RV-specific standards (ANSI/RVIA) and used for RVs and travel trailers only.

In addition, a NEMA 5-30P plug cannot fit into a TT-30R receptacle, and vice versa. Therefore, do not use a NEMA 5-30 outlet to power an RV because it will not match the plug and may damage electrical equipment if modified.

Electrical Ratings & Specifications

NEMA: 5-30R – Straight-Blade Receptacle
Poles: 2-Poles, 3 Wires Grounding – With Neutral
Voltage: 125V Single-Phase AC Supply – 60 Hz
Current: 30A -24A
Breaker / GFCI: 30A
Wattage: 3,600 W
Wire Size: #10 AWG Copper
Grade & Material: Commercial Grade – Nylon with Galvanized Steel
Mounting: Flush / Screw Mounting
Outdoor Box: 2-gang outdoor box – NEMA 3R rainproof enclosure
Wiring: Hardwired / Dedicated Circuit

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Wiring NEMA 5-30 Receptacle

Wiring 30A-125V Outlet using 1-P Breaker

The following wiring diagram illustrates the wiring connections of a 30A, 125V outlet (NEMA 5-30R) to a single-pole, 120V – 30A breaker or GFCI in a 120/240V main panel, as described below:

Before installation, strip the insulation from the conductors according to the connection type. Once completed, tighten all terminal screws to approximately 25 lb-in (3 N·m) of torque.

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 L-shaped or half-T slot terminal.

For this circuit, use #10 AWG copper wire, which is the correct size for a 30A circuit and the corresponding NEMA 5-30R outlet.

For outdoor installations of NEMA 5-30, use a NEMA 3R weatherproof 2-gang enclosure to protect the receptacle from moisture and environmental exposure.

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Wiring 30A-125V Outlet using 1-P, 30A GFCI Breaker

In the case of a 30A outlet used for RVs or outdoor installations where GFCI protection is required, simply replace the single-pole breaker with a single-pole, 30A-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

How Many Amps Can a 30A – 125V Receptacle Handle Safely?

A 30-amp, 120-volt outlet can safely handle up to 30 amps of continuous load. However, according to the NEC 80% rule (NEC 210.19(A)(1) and 210.20(A)), the continuous load should not exceed 24 amps (80% of 30A) for safety and to prevent overheating.

How Many Watts Can a 30A – 125V Receptacle Hold?

You can calculate the wattage using P = V × I:

Maximum: 120V × 30A = 3,600 watts
Safe continuous: 120V × 24A = 2,880 watts

Which Breaker Size is Suitable for a 30A – 125V Receptacle?

A single-pole, 30-amp breaker is the correct choice for a 30A-120V circuit. This breaker protects both the outlet and wiring from overload or short circuits.

For outdoor or RV applications where GFCI protection is required (per NEC 210.8(A)), use a single-pole, 30A GFCI breaker.

What is the Correct Wire Size and Cable Type to Use with a 30A-120V Receptacle?

For a 30A circuit, the minimum required conductor size must safely handle 30 amps per NEC Table 310.16, Table 210.24(1) and NEC 240.4(D)(8). Similarly, use the same size i.e. #10AWG for EGC as per NEC Table 250.122.

Recommended wire sizes:

Copper: 10 AWG (THHN, NM-B, or UF-B)
Aluminum: 8 AWG (if aluminum wiring is used)

Typical cable types:

Indoor: 10/2 NM-B (Black = Hot, White = Neutral, Bare = Ground)
Outdoor or buried: 10/2 UF-B or THWN in conduit

Instructions, Precautions & Codes

If your main purpose for installing the 5-30R outlet is for RVs, use an industrial-grade device with correct adapter.
It is recommended to hardwire instead of plug-in a 30-amp receptacle for welding machines.
The 5-30R 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, Table 210.24(1), and NEC 240.4(D)(8), the correct wire size for a 30A circuit and outlet is #10 AWG copper. Likewise, the appropriate breaker size is a 30A, 120V single-pole breaker (or 30A 1-P, GFCI breaker) when wiring a NEMA 5-30R receptacle, using the same wire size (#10 AWG) copper conductors.
A 30A outlet can supply up to a 24A continuous load and a maximum of 30A 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 30A-120V breaker and outlet.
Use 30A, 120V outlet as a dedicated circuit for single unit especially for RV and welding machine.

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.