30 Amp RV Hookup 100 Feet Away: What Size Wire?

1. A 30-amp RV outlet is a 120-volt circuit

The TT-30 plug on a travel trailer has two flat blades at an angle and a round ground pin. It carries one hot, one neutral and one ground, and the trailer runs on 120 V only. That single fact is what makes long runs hard: the current comes back on the neutral, so the voltage is lost on both conductors and is measured against 120 V, not 240 V.

The breaker is a standard 30 A single-pole breaker. Wiring the receptacle from a two-pole 240 V breaker is the most expensive mistake in this guide; it is covered under common mistakes below.

2. Ampacity: 10 AWG would be enough on paper

A 30 A breaker needs a conductor rated at least 30 A. Copper 10 AWG qualifies under the NEC ampacity table, and the small-conductor rule caps it at a 30 A breaker anyway. If the trailer were parked 25 ft from the panel, this guide would end here.

3. Voltage drop decides at 100 feet

Voltage drop for a 120 V circuit:

VD = 2 × L × I × R ÷ 1000, with L the one-way length in feet and R the conductor resistance in ohms per 1000 ft.

At the full 30 A and 100 ft:

The NEC recommends, in informational notes rather than a hard rule, about 3% for a branch circuit and 5% for feeder plus branch combined. Only 6 AWG meets 3% at full load. Remember that the utility voltage at your panel may already be a few volts below 120 V on a hot afternoon, and the trailer's own cord and wiring add a little more.

4. Full load or typical load?

A 30 A trailer rarely draws exactly 30 A for long, but it can sit close to it. Assume a realistic heavy afternoon of 24 A: the rooftop air conditioner running, the converter charging the battery and the electric element of the water heater on. That is our stated assumption; your trailer's mix will differ.

Even at the typical load, 10 AWG pushes the trailer close to the point where an air-conditioner compressor runs hot and an RV surge protector with low-voltage cutoff starts to trip. That is why we treat 10 AWG as unacceptable at 100 ft and pick between 8 and 6 AWG.

5. How the size changes with distance

Sizes below are the smallest copper conductor that carries 30 A and meets the stated drop at a full 30 A on 120 V.

Past about 125 ft, a 3% target pushes a 30 A circuit to 4 AWG, which is awkward to terminate. At that point many installers run a small 120/240 V feeder to an outdoor pedestal panel instead, or accept the 5% column.

6. The ground grows with the hots

When the circuit conductors are upsized for voltage drop, the NEC requires the equipment grounding conductor to be increased in proportion to their cross-sectional area. Normally a 30 A circuit needs a 10 AWG copper ground. Going from 10 AWG to 6 AWG multiplies the copper area by 2.53, so the ground has to grow by the same ratio, which lands at 6 AWG as well. In practice this means three equal conductors in the conduit: hot, neutral and ground.

7. Landing 6 AWG on a TT-30 receptacle

This is where theory meets the hardware. Many 30 A receptacles have terminals sized for 10 AWG, and 6 AWG simply will not fit. Your options:

• An RV power outlet box or pedestal with lugs sized for larger wire. Several listed outdoor units accept up to 6 AWG or larger and include the breaker and receptacle in one enclosure.
• A splice in a junction box next to the receptacle, from 6 AWG to short 10 AWG pigtails, with connectors listed for both sizes. The few inches of 10 AWG do not affect the drop.
• A small outdoor panel fed from the house, with the 30 A breaker at the post. This is the route if you might add a 50 A outlet later.

Whatever you choose, check the terminal rating marked on the device, and torque every connection to the value on its label.

8. Wiring method for the trench

The run is outdoors and underground, so it is a wet location from end to end.

• THWN-2 individual conductors in PVC conduit is the most flexible approach and makes it easy to pull larger wire later.
• UF-B cable rated for direct burial also works; it is sized from the 60 °C column, which does not change the answer here because voltage drop, not ampacity, sets the size.
• NM-B is not permitted anywhere in this run, not even inside the conduit.
• Respect the burial depth for the method you use and protect the riser where it leaves the ground.
• The receptacle needs GFCI protection under recent NEC editions for outdoor receptacles at dwellings. A GFCI breaker at the panel or a GFCI-protected pedestal both satisfy it.

9. Before the inspection: a checklist

• [ ] 30 A single-pole breaker, listed for the panel
• [ ] 6 AWG copper hot and neutral, ground upsized in proportion
• [ ] THWN-2 in conduit or UF-B, no NM-B anywhere outdoors
• [ ] TT-30R receptacle in a weatherproof, in-use cover
• [ ] GFCI protection in place and tested
• [ ] Polarity checked: 120 V hot to neutral, 0 V neutral to ground, 120 V hot to ground
• [ ] Terminations torqued; any splice made with connectors rated for both wire sizes

10. Signs the run is undersized

• The air conditioner hums, short-cycles or trips its own overload on hot days.
• Your plug-in surge protector or energy management system reports low voltage and disconnects.
• The plug or receptacle feels warm after an hour of heavy load. That points to a loose or worn connection, not only to wire size, and should be fixed before the next use.

11. Common mistakes

• Wiring a TT-30R to 240 V. A two-pole breaker with both hots on the receptacle puts 240 V into a 120 V trailer and can destroy the converter, microwave and air conditioner in seconds. Measure 120 V hot to neutral before plugging in.
• Using a dryer receptacle. A 10-30 or 14-30 outlet is a 240 V device. Adapters from 14-30 to TT-30 exist for specific wiring, but they are not a substitute for a dedicated 120 V circuit.
• Sizing from the breaker alone. 10 AWG is correct for a 30 A circuit at short distance and wrong at 100 ft.
• Forgetting the ground. Upsizing the hots and keeping a 10 AWG ground is a common inspection failure.
• Daisy-chained extension cords to cover the last 20 ft. They add their own drop and their own heat.

Case summary

FAQ

Can I use 10/2 UF for a 30 amp RV outlet 100 feet away? It is legal on ampacity, but it drops 7.3 V at 30 A, which is 6.0% of 120 V. Expect air-conditioner trouble. Use 8 AWG at minimum.

Is 8 AWG good enough at 100 feet? At a full 30 A it drops 3.82%, inside the 5% total that the NEC notes suggest. At our assumed 24 A it drops 3.06%. Many owners find that acceptable; 6 AWG is the better choice if the trailer will be lived in during summer.

What about 150 feet? To stay under 3% at full load you need 4 AWG copper (2.31%). At that distance a small outdoor subpanel often makes more sense.

Does the trailer's own 25-foot cord count? Yes. Its drop adds to the drop in your buried run. Keep the RV's cord as short as possible and do not add extension cords.

Different distance or a 50 A coach? Run the wire size calculator with your own numbers, and have a licensed electrician pull the permit for the outdoor circuit.