What Size Wire for a 30 Amp RV Outlet 100 Feet Away?
Voltage drop
3.11% on the run
240 volts, single phase, 30 amps, 100 feet one way, 10 AWG copper.
Between 3 and 5 percent. Legal, and still worth fixing on a branch circuit that feeds a motor, a heater or a long lighting run. Going up to 8 AWG brings it under 3 percent.
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How that number is worked out
These are the figures this page was built with and every line the calculator produces from them. Change anything above and all of it moves.
- System voltage240 V
- PhaseSingle phase
- Load current30 A
- One way run length100 ft
- Conductor size10 AWG
- Conductor materialCopper
Voltage drop3.11% on the run
Between 3 and 5 percent. Legal, and still worth fixing on a branch circuit that feeds a motor, a heater or a long lighting run. Going up to 8 AWG brings it under 3 percent.
| Drop | 7.46 V |
|---|---|
| Voltage at the load | 232.5 Vfrom 240 V at the panel |
| Smallest conductor under 3% | 8 AWG |
| Longest run at 10 AWG under 3% | 97 ftone way |
| Conductors to pull | 3including the equipment ground |
The material list this produces
| 10 AWG copper conductor, ft | 330 |
|---|---|
| Conduit or cable, ft | 110 |
| Breaker, 30 A, each | 1 |
| Terminations and lugs, each | 6 |
One way run length compared
Drop is a straight line in length. Double the run and you double the drop, which is why the same wire that is fine in a basement is not fine across a yard.
| One way run length | Voltage drop | Smallest conductor under 3% |
|---|---|---|
| 50 ft | 1.55% on the run | 12 AWG |
| 100 ft | 3.11% on the run | 8 AWG |
| 150 ft | 4.66% on the run | 8 AWG |
| 200 ft | 6.21% on the run | 6 AWG |
| 300 ft | 9.32% on the run | 4 AWG |
What else matters here
Ten AWG is the correct ampacity for 30 amps and at 100 feet it lands at 3.11 percent, which is just past the guideline. Ten AWG holds 3 percent out to 97 feet on this circuit, so this run misses by three feet.
In practice most people pull 8 AWG for an RV pedestal anyway, and it is the right call. An RV plugged in for a week runs an air conditioner and a water heater on a circuit that is already near its limit, which is exactly the sustained load case where drop matters.
Note the voltage. A 30 amp RV service, the TT-30, is 120 volts, not 240, and at 120 volts this same 10 AWG run drops over 6 percent. If the outlet is a TT-30 rather than a 14-50, switch the voltage above to 120 and size from that number instead.
What this calculator assumes
- The formula is the standard one: drop equals 2 times K times amps times the one way length, divided by the circular mil area of the conductor. Three phase uses 1.732 in place of the 2.
- K is 12.9 for copper and 21.2 for aluminum, the usual figures for a conductor running warm in conduit. Circular mil areas come from NEC Chapter 9, Table 8.
- Enter the one way distance, not the loop. The formula doubles it for you, because current has to get back.
- The 3 percent branch circuit and 5 percent total figures in 210.19 and 215 are informational notes rather than requirements. Nobody fails an inspection on voltage drop alone, but motors, LED drivers and long well pump runs care a great deal.
Questions people ask
What size wire for a 30 amp RV outlet 100 feet away?
8 AWG copper is the sensible choice. 10 AWG meets the ampacity requirement and lands at 3.11 percent over 100 feet at 240 volts, which is just past the guideline, and considerably worse on a 120 volt TT-30.
Is an RV 30 amp outlet 120 or 240 volts?
A TT-30 is 120 volts on a 30 amp breaker. A 14-50, the one most larger RVs use, is 240 volts at 50 amps. They are not interchangeable and the voltage changes the wire size answer completely.
Is 3 percent voltage drop actually required by code?
No. The 3 percent branch circuit figure and the 5 percent total figure live in informational notes to NEC 210.19 and 215, and informational notes are advisory rather than enforceable. Some jurisdictions adopt them as local amendments and many engineered specs require them, and motors and electronics behave badly on a long undersized run whatever the code says.
The voltage drop calculator takes any dimensions you like and hands back the same list.