Reference
RV 12V Voltage Drop Chart by Wire Gauge, Current and Length
Researched from published standards and manufacturer specifications. Updated .
Quick answer
Voltage drop volts equal 2 x one-way length in feet x amps x (ohms per 1000 ft / 1000). The 2 accounts for the return conductor, and forgetting it is the most common RV wire sizing error. ABYC E-11 caps critical 12V circuits at 3 percent (0.36V) and non-critical circuits at 10 percent (1.2V). A 6 AWG conductor at 50A over a 10 ft one-way run drops 0.98V, or 8.18 percent, well past the critical limit and into non-critical territory only.
On a 12V RV system, voltage drop almost always governs conductor size before ampacity does. Three percent of 12V is only 0.36V, a limit that a short, high-current run can blow through with wire that is otherwise rated for far more current than it is actually carrying. The tables below compute exact drop using the same formula and the same NEC Chapter 9, Table 8 copper resistance figures this site's calculators use, so a number you read here matches what the wire gauge calculator returns for the same inputs.
Every table on this page uses one-way length as the input and doubles it internally for the round trip, because current has to return to the battery on the negative conductor and that conductor drops voltage too. A 10 ft one-way run is 20 ft of actual copper. Ampacity still matters and is covered on the wire gauge ampacity chart; this page is about the number that usually decides the gauge first.
How much voltage do you lose over a 10 ft one-way wire run?
This table is the everyday reference: pick your gauge, read across to your current, and see the drop in volts and as a percent of 12V. Anything past 3 percent fails ABYC's critical circuit limit, and anything past 10 percent fails even the non-critical limit.
| AWG | 10A | 20A | 50A | 100A | 150A | 200A |
|---|---|---|---|---|---|---|
| 14 | 0.628V (5.23%) | 1.256V (10.47%) | 3.14V (26.17%) | 6.28V (52.33%) | 9.42V (78.5%) | 12.56V (104.67%) |
| 12 | 0.396V (3.3%) | 0.792V (6.6%) | 1.98V (16.5%) | 3.96V (33%) | 5.94V (49.5%) | 7.92V (66%) |
| 10 | 0.248V (2.07%) | 0.496V (4.13%) | 1.24V (10.33%) | 2.48V (20.67%) | 3.72V (31%) | 4.96V (41.33%) |
| 8 | 0.156V (1.3%) | 0.311V (2.59%) | 0.778V (6.48%) | 1.556V (12.97%) | 2.334V (19.45%) | 3.112V (25.93%) |
| 6 | 0.098V (0.82%) | 0.196V (1.64%) | 0.491V (4.09%) | 0.982V (8.18%) | 1.473V (12.28%) | 1.964V (16.37%) |
| 4 | 0.062V (0.51%) | 0.123V (1.03%) | 0.308V (2.57%) | 0.616V (5.13%) | 0.924V (7.7%) | 1.232V (10.27%) |
| 2 | 0.039V (0.32%) | 0.078V (0.65%) | 0.194V (1.62%) | 0.388V (3.23%) | 0.582V (4.85%) | 0.776V (6.47%) |
| 1 | 0.031V (0.26%) | 0.062V (0.51%) | 0.154V (1.28%) | 0.308V (2.57%) | 0.462V (3.85%) | 0.616V (5.13%) |
| 1/0 | 0.024V (0.2%) | 0.049V (0.41%) | 0.122V (1.02%) | 0.244V (2.03%) | 0.366V (3.05%) | 0.488V (4.07%) |
| 2/0 | 0.019V (0.16%) | 0.039V (0.32%) | 0.097V (0.81%) | 0.193V (1.61%) | 0.29V (2.42%) | 0.387V (3.22%) |
| 4/0 | 0.012V (0.1%) | 0.024V (0.2%) | 0.061V (0.51%) | 0.122V (1.01%) | 0.182V (1.52%) | 0.243V (2.03%) |
Published standard Source: NEC Chapter 9, Table 8, DC resistance of uncoated stranded copper at 75 C, applied with drop volts = 2 x length x amps x (ohms per 1000 ft / 1000).
The same wire on a 25 ft one-way run
Doubling the length does not double the drop by coincidence, it doubles it exactly, because the formula is linear in length. A run that passed at 3 percent over 10 ft can fail the same limit over 25 ft with no change to gauge or current.
| AWG | 10A | 20A | 50A | 100A | 150A | 200A |
|---|---|---|---|---|---|---|
| 14 | 1.57V (13.08%) | 3.14V (26.17%) | 7.85V (65.42%) | 15.7V (130.83%) | 23.55V (196.25%) | 31.4V (261.67%) |
| 12 | 0.99V (8.25%) | 1.98V (16.5%) | 4.95V (41.25%) | 9.9V (82.5%) | 14.85V (123.75%) | 19.8V (165%) |
| 10 | 0.62V (5.17%) | 1.24V (10.33%) | 3.1V (25.83%) | 6.2V (51.67%) | 9.3V (77.5%) | 12.4V (103.33%) |
| 8 | 0.389V (3.24%) | 0.778V (6.48%) | 1.945V (16.21%) | 3.89V (32.42%) | 5.835V (48.63%) | 7.78V (64.83%) |
| 6 | 0.245V (2.05%) | 0.491V (4.09%) | 1.228V (10.23%) | 2.455V (20.46%) | 3.683V (30.69%) | 4.91V (40.92%) |
| 4 | 0.154V (1.28%) | 0.308V (2.57%) | 0.77V (6.42%) | 1.54V (12.83%) | 2.31V (19.25%) | 3.08V (25.67%) |
| 2 | 0.097V (0.81%) | 0.194V (1.62%) | 0.485V (4.04%) | 0.97V (8.08%) | 1.455V (12.13%) | 1.94V (16.17%) |
| 1 | 0.077V (0.64%) | 0.154V (1.28%) | 0.385V (3.21%) | 0.77V (6.42%) | 1.155V (9.63%) | 1.54V (12.83%) |
| 1/0 | 0.061V (0.51%) | 0.122V (1.02%) | 0.305V (2.54%) | 0.61V (5.08%) | 0.915V (7.63%) | 1.22V (10.17%) |
| 2/0 | 0.048V (0.4%) | 0.097V (0.81%) | 0.242V (2.01%) | 0.483V (4.03%) | 0.725V (6.04%) | 0.967V (8.06%) |
| 4/0 | 0.03V (0.25%) | 0.061V (0.51%) | 0.152V (1.27%) | 0.304V (2.53%) | 0.456V (3.8%) | 0.608V (5.07%) |
Published standard Source: Same NEC Chapter 9, Table 8 resistance figures and formula as the 10 ft table above, at 25 ft one-way.
The longest one-way run that stays inside 3 percent (critical circuits)
This is the reverse lookup: instead of drop at a fixed length, this table gives the maximum one-way length in feet before a gauge and current combination crosses ABYC's 3 percent critical limit of 0.36V. Ampacity is a separate check, covered on the wire gauge ampacity chart, and the smaller of the two limits always wins.
| AWG | 10A | 20A | 30A | 50A | 100A | 150A | 200A |
|---|---|---|---|---|---|---|---|
| 14 | 5.7 | 2.9 | 1.9 | 1.1 | 0.6 | 0.4 | 0.3 |
| 12 | 9.1 | 4.5 | 3.0 | 1.8 | 0.9 | 0.6 | 0.5 |
| 10 | 14.5 | 7.3 | 4.8 | 2.9 | 1.5 | 1.0 | 0.7 |
| 8 | 23.1 | 11.6 | 7.7 | 4.6 | 2.3 | 1.5 | 1.2 |
| 6 | 36.7 | 18.3 | 12.2 | 7.3 | 3.7 | 2.4 | 1.8 |
| 4 | 58.4 | 29.2 | 19.5 | 11.7 | 5.8 | 3.9 | 2.9 |
| 2 | 92.8 | 46.4 | 30.9 | 18.6 | 9.3 | 6.2 | 4.6 |
| 1 | 116.9 | 58.4 | 39.0 | 23.4 | 11.7 | 7.8 | 5.8 |
| 1/0 | 147.5 | 73.8 | 49.2 | 29.5 | 14.8 | 9.8 | 7.4 |
| 2/0 | 186.1 | 93.1 | 62.0 | 37.2 | 18.6 | 12.4 | 9.3 |
| 4/0 | 296.1 | 148.0 | 98.7 | 59.2 | 29.6 | 19.7 | 14.8 |
Published standard Source: Derived from the NEC Chapter 9, Table 8 resistance figures at the ABYC E-11 3 percent critical circuit drop limit for 12V. A conductor still has to pass its ampacity table separately. This length only clears the voltage drop test.
The longest one-way run that stays inside 10 percent (non-critical circuits)
Lighting and general accessory circuits get more slack under ABYC E-11, a 10 percent drop limit rather than 3 percent. That is 1.2V on a 12V system instead of 0.36V, and it lets the same gauge run more than three times as far for the same current.
| AWG | 10A | 20A | 30A | 50A | 100A | 150A | 200A |
|---|---|---|---|---|---|---|---|
| 14 | 19.1 | 9.6 | 6.4 | 3.8 | 1.9 | 1.3 | 1.0 |
| 12 | 30.3 | 15.2 | 10.1 | 6.1 | 3.0 | 2.0 | 1.5 |
| 10 | 48.4 | 24.2 | 16.1 | 9.7 | 4.8 | 3.2 | 2.4 |
| 8 | 77.1 | 38.6 | 25.7 | 15.4 | 7.7 | 5.1 | 3.9 |
| 6 | 122.2 | 61.1 | 40.7 | 24.4 | 12.2 | 8.1 | 6.1 |
| 4 | 194.8 | 97.4 | 64.9 | 39.0 | 19.5 | 13.0 | 9.7 |
| 2 | 309.3 | 154.6 | 103.1 | 61.9 | 30.9 | 20.6 | 15.5 |
| 1 | 389.6 | 194.8 | 129.9 | 77.9 | 39.0 | 26.0 | 19.5 |
| 1/0 | 491.8 | 245.9 | 163.9 | 98.4 | 49.2 | 32.8 | 24.6 |
| 2/0 | 620.5 | 310.2 | 206.8 | 124.1 | 62.0 | 41.4 | 31.0 |
| 4/0 | 986.8 | 493.4 | 328.9 | 197.4 | 98.7 | 65.8 | 49.3 |
Published standard Source: Derived from the NEC Chapter 9, Table 8 resistance figures at the ABYC E-11 10 percent non-critical circuit drop limit for 12V.
When the fix is a higher system voltage instead of a bigger wire
Every table on this page holds current fixed and solves for gauge or length, but current itself is not fixed if the system voltage can change. Doubling system voltage from 12V to 24V for the same power halves the current, and since drop scales with current, the percentage drop for the same power and the same gauge falls by a factor of four, not just two. A run that fails the 3 percent limit badly at 12V can pass comfortably at 24V on the identical wire, which is why some owners with long runs or very high current loads move the whole house system to 24V rather than chasing an ever-heavier gauge. That decision affects every component downstream, not just the wiring, and the 12V versus 24V comparison covers the full tradeoff.
The 2 in the drop formula is not optional. Halving it by forgetting the return conductor undersizes a cable by roughly a factor of two, and that error shows up as dim lights, a converter that never seems to reach full charge, or an inverter that trips on a load it should easily carry.
Cable sized to this chart
4 AWG Battery Inverter Cable, 2 ft Pair
$20.99A slightly longer 2 ft pair in the same gauge, for a jump that does not fit an 18 in cable.
Best for: Inverter to battery on a short run.
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Blue Sea Systems m-Series On/Off Battery Switch
$27.05A battery disconnect belongs in the same run as any cable size pulled from this chart.
Best for: A main disconnect you trust.
Check price on AmazonFrequently asked questions
- Why does voltage drop matter more than ampacity on a 12V RV system?
- Because the allowed drop is a small absolute number at 12V. ABYC E-11 allows 3 percent for critical circuits, and 3 percent of 12V is only 0.36V. A conductor can be well within its ampacity rating and still fail that drop test on a run of just a few feet at high current, which is why length and current decide the gauge before the ampacity table gets consulted at all.
- What is the ABYC voltage drop limit for a 12V RV circuit?
- ABYC E-11 sets 3 percent for critical circuits, which covers panel feeds, electronics, and anything whose failure is a safety issue, and 10 percent for non-critical circuits such as lighting and general accessories. On 12V that works out to 0.36V and 1.2V respectively. Both limits apply to the round trip drop, not the drop over the one-way distance alone.
- Why does the round trip length matter and not just the one-way distance?
- Current has to travel out to the load on the positive conductor and back to the battery on the negative conductor, and both conductors have resistance that drops voltage. A 10 ft one-way run is actually 20 ft of current-carrying copper. The formula on this page multiplies one-way length by 2 for exactly this reason, and skipping that step is the single most common RV wire sizing mistake.
- Does a bigger battery bank fix voltage drop?
- No. Voltage drop is a property of the wire, the current, and the length, not of the battery bank's capacity. A larger bank changes how long a load can run, not how much voltage is lost getting current from the bank to the load. Fixing drop means a shorter run, a heavier gauge, or a higher system voltage where the same power moves at less current.
- What is the difference between the ABYC and NEC ampacity tables for RV wiring?
- ABYC E-11 covers 105 C insulation outside engine spaces and publishes higher ampacity figures because it assumes high-temperature insulation and open mounting, which is common for 12V house wiring. NEC Table 310.16 covers 75 C copper in a raceway with other conductors, a more conservative assumption. The two tables should never be mixed within one calculation, and this site states which one a given result used.
- How much does a marginal voltage drop actually cost in performance?
- A drop right at the 3 percent limit means the load sees roughly 11.6V instead of 12V, which can dim lights, slow a water pump, or make an inverter work harder for the same output. Electronics that expect a stable 12V can behave erratically closer to the 10 percent limit. The published limits exist because real equipment starts to misbehave well before total failure.
Read length before current, and current before gauge. The tables above compute exactly what the wire gauge calculator computes for the same numbers, so run your own amps and one-way length through it once you know which table row you are near.