How to Wire a 30A, NEMA 10-30 Non-Grounding Receptacle

Electrical Technology

How to Replace a 30A, 125/250V, NEMA 10-30 Receptacle with a 2P Breaker in Existing Installations?

The NEMA 10-30 is a 3-wire, non-grounding receptacle and does not require an equipment ground. It is no longer permitted for new installations and may only be replaced in existing installations. For new work, use a NEMA 14-30 or 6-30 receptacle with a grounding conductor.

A NEMA 10-30R is an older electrical receptacle commonly used in homes built before 1996 for 3-prong electric dryers. It is a 240-volt, 30-amp connection that provides two hot wires and a neutral wire, but lacks a dedicated ground wire, which is less safe than modern 4-prong NEMA 14-30R or 3-prong NEMA 6-30 receptacles and outlets.

Good to Know: Since 2-wire non-grounding receptacles are no longer permitted for new installations, NEC 406.4(D)(2) and 250.130(C) allow their replacement only under the following conditions:

1. Replace with another 2-wire receptacle:

You may replace the existing non-grounding receptacle with a new one of the same type.

2. Replace with a GFCI receptacle:

A GFCI-type receptacle may be installed as a replacement. In this case, the receptacle must be clearly marked with the words “No Equipment Ground” and/or “GFCI Protected” to indicate that it is not connected to an equipment grounding conductor.

3. Replace with a grounding-type receptacle protected by a GFCI:

A grounding-type receptacle may be installed if it is protected by a GFCI device, such as a GFCI circuit breaker or a GFCI receptacle located at the first outlet on the circuit. In this configuration, the GFCI provides shock protection even though an equipment grounding conductor (EGC) is not present.

When replacing a damaged NEMA 10-30 receptacle in an existing electrical setup, get an industrial grade instead of residential grade. Also, use a 30A, 2-pole breaker, or a GFCI breaker if required by local electrical codes. Keep in mind that using a GFCI breaker with a NEMA 10-30 receptacle may cause nuisance tripping, when the neutral is bonded to the appliance frame. Additionally, the receptacle does not have a separate equipment grounding conductor which is needed for proper GFCI operation.

NEC 250.140(A) and (B) explicitly require the use of a four-wire supply for electric ranges, ovens, and clothes dryers, which must include an equipment grounding conductor (EGC).
NEC 250.119(A) mandates a dedicated grounding conductor for all receptacle outlets. The NEMA 10-30, with its two-hot and one-neutral (three-prong) design, lacks this grounding provision. For safety, alternatives such as NEMA 14-30 or NEMA 6-30 are used instead of the 10-30.

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The NEMA 10-30 Receptacle

The NEMA 10-30R is a 30-amp, 125/250V, non-grounding receptacle. It is wired with two hot wires and a neutral wire and is designed to be used with a matching NEMA 10-30P plug. The “50” in 10-30R indicates the maximum current rating in amperes, while the “R” stands for “Receptacle.” Similarly, the “P” in NEMA 10-30P stands for “Plug.”

The NEMA 10-30 has a 3-pole, 3-wire configuration (Hot 1, Hot 2, and Neutral). It is a non-grounding, straight-blade device that does not include a dedicated grounding conductor. It has two angled hot slots (for Hot 1 and Hot 2) and one “L” shape slot for the neutral wire.

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Terminals

There are 3 terminals in a NEMA 10-30 receptacle:

X Terminal (Brass Screw): Connects to HOT 1 (Line 1) – Black Wire
Y Terminal (Brass Screw): Connects to HOT 2 (Line 2) – Red Wire
W Terminal (Silver Screw): Connects to the Natural – White Wire

Electrical Ratings & Specifications

NEMA: NEMA 10-30R – Straight-Blade Receptacle
Poles: 3-Pole, 3-Wire – Non-Grounding with Neutral
Wires: 3 Wires – Hot 1, Hot 2 and Neutral
Voltage: 125/250V Single-Phase AC Supply – 60 Hz
Breaker: 30A
Current: 30A – 24A
Wattage: 7,200 W
Wire Size: #8 to #10 AWG (Copper Only)
Temp. Rating: -40°C to 75°C (-40°F to 167°F)
Dielectric-strength: Withstand 2,000V Min.
Options: Residential and Industrial Grade
Mounting: Flush / Surface Mounting
Outdoor Box: 2-gang outdoor box – NEMA 3R rainproof enclosure
Wiring: Hardwired / Dedicated Circuit

Wiring NEMA 10-30 Receptacle with a 2P Breaker

A NEMA 10-30 receptacle can be installed as a replacement for either a plug-in or hardwired connection in an existing electrical setup.

According to the wiring diagram, connect Hot 1 (black wire) and Hot 2 (red wire) from a 2-pole, 30A breaker to the “X” and “Y” terminals of the NEMA 10-30 receptacle. Then, connect the neutral (white wire) to the L-shaped “W” terminal of the receptacle in a 120/240V or 208/240V electrical system.

For this configuration, use #10 AWG copper conductors for the 30A circuit and the corresponding NEMA 10-30R outlet

Good Practice

Strip each conductor 1 inch (25mm) or refer to the stripe gage on mounting plate.
Tighten terminal screws to approximately 25 lb-in (3.0 N·m).

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For outdoor installations, a NEMA 3R weatherproof (rainproof) 2-gang enclosure should be used to protect the receptacle from moisture and environmental exposure.

Good to Know:

NEMA 10-30 outlets are not intended for grounding use. They must be connected only to non-grounding circuits, unless used for ranges or clothes dryers in accordance with NEC 250.60.
Per NEC 210.8, GFCI protection is required for receptacles located in garages, basements, outdoors, laundry areas, and other wet or damp locations. In fact, NEC 210.8(A)(1) through (A)(11) mandates that all outdoor receptacles be installed downstream of GFCI protection, in compliance with Articles 426.28 and 427.22.
Be aware that nuisance tripping may occur when using a GFCI breaker with a non-grounding receptacle, especially if the neutral is bonded to the frame. In such cases, always follow the manufacturer’s recommendations to prevent overlapping protection issues.

FAQs:

How Many Amps Can a NEMA 10-30 Handle Safely?

A NEMA 10-30 receptacle is rated for 30 amps maximum. For continuous loads, the NEC recommends using only 80% of its rating, which equals 24 amps.

How Many Watts Can a NEMA 10-30 Receptacle Hold?

At 240 volts, a 30-amp 10-30 receptacle can handle up to 7,200 watts (30A × 240V). For continuous loads, it is limited to 5,760 watts (24A × 240V).

Which Breaker Size is Suitable for a 10-30 Receptacle?

The right size breaker is 30-amp double-pole breaker of GFCI for a NEMA 10-30 receptacle .

What is the Correct Wire Size and Cable Type to Use with NEMA 10-30?

Suitable Wire Size: #10 AWG copper (Based on NEC Table – 310.16).
Cable Type: Commonly 10/3 NM-B (with ground) or 10/3 SR/SE cable. Note: The NEMA 10-30 is a 3-wire (hot-hot-neutral) receptacle and does not use an equipment grounding conductor.

Can You Use NEMA 10-30 for EV Charging?

While possible with an adapter, it is not recommended because the 10-30R lacks a dedicated ground. EVSE manufacturers and the NEC recommend using grounded receptacles like NEMA 14-30 or NEMA 6-30 for EV charging.

Can You Install NEMA 10-30 in New Installations?

No. Per NEC requirements, NEMA 10-30 receptacles are not allowed in new installations. They are permitted only as replacements in existing installations.

How Can I Replace a NEMA 10-30 with NEMA 6-30 Without Running an Additional Wire?

You cannot directly convert a NEMA 10-30 (3-wire, no ground) to a NEMA 6-30 (3-wire, hot-hot-ground) without installing a dedicated grounding conductor.

Alternatively, you may remark and connect the neutral wire from “W” terminal of the NEMA 10-30 to the ground wire and connect to the “G” terminal of the NEMA 6-30. Since the ground wire is bonded to the neutral in the main panel, it will perfectly serve the circuit.

By doing so, it is strongly advised that when repurposing the neutral as a ground, the conductor must be clearly marked with an identifying note or label.

Warning

Always disconnect the power supply by switching OFF the breaker in the main service panel before performing any electrical work.
If you are not confident or qualified, consult a licensed electrician to ensure the installation is performed safely and in compliance with local electrical codes.
The author assumes no responsibility for any losses, injuries, or damages resulting from the use or misuse of the information provided. Electricity is extremely dangerous! please exercise caution and never attempt wiring unless you fully understand the process.

Resources:

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