An AC wire size calculator answers one question: what conductor must carry this AC current safely, over this distance, at this voltage and phase? The answer matters because the wire is the physical link between your AC supply and your equipment, and AC brings two complications that DC never does.
The maximum current a conductor can carry continuously before its insulation overheats. Depends on material, temperature rating, and conductor count. Same for AC and DC — thermal limit doesn't care about alternation.
For AC, impedance has two parts: resistance and reactance. Power factor also counts — a reactive AC load draws more current, and more current means more drop.
The result — the AWG number or mm² cross-section you write on the order. A 30 A circuit needs 10 AWG for a short run; at 50 metres single-phase it pushes to 8 AWG or bigger.
A 30 A circuit needs 10 AWG copper for a short run. Run that same circuit 50 metres at 240 V single-phase and the AC voltage drop pushes you to 8 AWG or bigger. At 400 V three-phase, the same current stays on 10 AWG for a much longer run, because three-phase AC uses √3 instead of the 2× round-trip factor. That phase-dependent distance rule is exactly what this AC wire size calculator handles for every entry.
Covers both phase systems at the AC voltages used in 50 Hz and 60 Hz markets, plus custom voltage entry.
Applies the 2× round-trip factor for single-phase and the √3 factor for three-phase, with the formula shown beside every result.
Defaults to 0.8 for motor and generator loads — so you never undersize a reactive AC load. PF changes the current, and the calculator accounts for it.
Pick a generator size — it returns the full-load AC current and the correct output cable from the genset to your distribution board, ending in a free factory-direct quote.
Size AC conductors for any voltage and distance. The calculator handles single-phase (2× round-trip) and three-phase (√3 factor), checks ampacity and AC voltage drop with power factor, and returns AWG and mm².
Enter the current or load. The calculator applies the 2× round-trip distance for voltage drop.
Enter the current or load. The calculator applies the √3 factor for line-to-line voltage drop.
Select a generator size. The calculator returns the full-load AC current and the recommended output cable.
This chart shows the allowable ampacity of copper conductors from NEC Table 310.16 at the three insulation temperature ratings, assuming up to three current-carrying conductors at 30 °C ambient. It applies to AC and DC alike — the thermal limit of the conductor is the same for both, and it is the starting point for every AC wire sizing calculation. Use it to sanity-check a result; the AC wire size calculator above applies the same values with derating and the AC voltage-drop checks.
| AWG | 60 °C | 75 °C | 90 °C |
|---|---|---|---|
| 14 | 20 A | 25 A | 30 A |
| 12 | 25 A | 30 A | 35 A |
| 10 | 30 A | 35 A | 40 A |
| 8 | 40 A | 50 A | 55 A |
| 6 | 55 A | 65 A | 75 A |
| 4 | 70 A | 85 A | 95 A |
| 3 | 85 A | 100 A | 115 A |
| 2 | 95 A | 115 A | 130 A |
| 1 | 110 A | 130 A | 145 A |
| 1/0 | 125 A | 150 A | 170 A |
| 2/0 | 145 A | 175 A | 195 A |
| 3/0 | 165 A | 200 A | 225 A |
| 4/0 | 195 A | 230 A | 260 A |
AC wire sizing is a two-step process. First size for ampacity: the conductor must carry the circuit current without overheating. Then check voltage drop: the conductor must keep the AC voltage loss within limits over the run length. The final size is the larger of the two, and on runs longer than about 30–50 metres, voltage drop usually wins.
Select the conductor whose rating equals or exceeds the circuit current after derating. For a continuous load (3+ hours), size for 125% of full-load current — per NEC 215.3 and BS 7671.
Single-phase: Vdrop = 2 × L × I × Z ÷ 1,000
Three-phase: Vdrop = √3 × L × I × Z ÷ 1,000
L = one-way length (m), I = current (A), Z = AC impedance/m.
No more than 3% voltage drop on a branch circuit, and 5% total from source to load. If the drop exceeds the limit, move up one conductor size and re-check.
A 10 A heater on 240 V, run 60 m on 2.5 mm² copper. Drop = 2 × 60 × 10 × 0.0074 = 8.9 V (3.7%). Over the 3% branch limit — move up to 4 mm².
A 30 kW motor at 400 V, 0.85 PF draws 51 A. 16 mm² copper over 100 m drops 2.5% — OK. Double to 200 m → nears 5% → 25 mm² needed.
The National Electrical Code (NFPA 70) sets out the ampacity tables and derating rules. BS 7671 (IET) sets out the equivalent for metric cable. Both agree: ampacity first, voltage drop second, and the bigger conductor wins.
DC and single-phase AC both use the 2× round-trip distance. Three-phase AC uses √3 instead. And AC adds power factor and reactance. The same conductor, current, and distance can produce very different voltage drops depending on the system.
2× round-trip — resistance only. No power factor or reactance. The simplest system to size, but low voltage often demands thick conductors.
2× round-trip + power factor + reactance. A 30 kW load at 0.8 PF draws 25% more current than its kW implies — the wire must carry that full current.
√3 (1.732) instead of 2×. Drops about 13% less than single-phase on the same conductor, current, and distance. Three-phase feeders can run further on smaller cable.
A motor, pump, or compressor draws more current than its kW suggests because part of the current is reactive. At 0.8 PF, a 30 kW load draws 25% more current — AC sizing can never ignore PF.
AC also meets inductive reactance that DC never sees. Small for most runs, but grows with current and on large conductors — another reason AC drop is never exactly DC drop.
The ampacity chart is the same for AC and DC — the thermal limit doesn't care whether current alternates. The difference lives entirely in the voltage-drop step. Never blur this distinction.
The AC voltage you run on decides the ampacity size and how far the run can go. The calculator applies 120 V, 208 V, 230 V, 240 V, 400 V, 415 V, and 480 V with the exact voltage-drop check for each.
14 AWG — fine to ~15 m. Low voltage gives a tiny drop budget, so runs over 15 m force an upsize. Always check the distance.
30 A: 10 AWG to ~25 m. 50 A: 6 AWG, upsize to 4 AWG over ~30 m. Single-phase drops twice as fast as three-phase.
Lower voltage than 240 V means more current for the same power. Use the calculator with the exact voltage — 208 V changes the ampacity and distance compared to 240 V.
2 AWG (33.6 mm²) — upsize to 1/0 over ~50 m. Three-phase feeders go much further than single-phase on the same cable.
Higher voltage means lower current for the same power. A 100 A circuit at 480 V often stays on 2 AWG for 50 m where 208 V would need an upsize.
Size for distance, then confirm. A 50 A circuit at 240 V single-phase drops twice as fast as the same 50 A on a 400 V three-phase feeder. The calculator computes the exact value for your voltage, phase, and run length. If you need the answer in both AWG and mm², the general electrical wire size calculator returns both systems in one pass.
Our engineers will review your AC circuit sizing, confirm the voltage drop, and deliver a factory-direct price — no obligation, no hidden fees. Every quote includes the generator, output cable, and automatic transfer switch for a complete AC power solution.
A: Partly. Ampacity is identical, the thermal rating of a conductor does not change with AC or DC. The difference is in voltage drop: single-phase AC adds power factor and reactance on top of resistance, and three-phase AC replaces the 2× round-trip distance factor with √3. The result is that AC circuits often need a larger conductor than a DC calculation would suggest, especially for reactive loads.
A: Single-phase AC uses a 2× round-trip distance for voltage drop, because current travels out and back. Three-phase AC uses √3 (1.732) instead, so it drops about 13% less voltage than single-phase on the same conductor, current, and distance. Three-phase feeders can therefore run further on the same cable size.
A: For a short run, 10 AWG copper carries 30 A at 75 °C. At 240 V single-phase, that holds to about 25 metres; beyond that, upsize to 8 AWG to keep the AC voltage drop within limits. Enter your run in the AC wire size calculator to confirm the correct 240 V wire size.
A: 6 AWG copper carries 50 A for a normal run. Over about 30 metres at 240 V single-phase, the voltage drop forces a move to 4 AWG. Use 8 AWG for 40 A, 6 AWG for 50 A, and check the distance every time.
A: Yes, directly. A motor at 0.8 power factor draws about 25% more current than its kW rating implies, and the conductor must carry that full current. Sizing an AC circuit at power factor 1.0 undersizes the wire and the drop grows accordingly. This is the most common AC sizing error in the field.
A: At the 50 Hz and 60 Hz mains frequencies used in power systems, the difference in reactance and skin effect is small for typical conductor sizes. On very large conductors, or at higher frequencies (for example aircraft or industrial 400 Hz systems), skin effect grows and can force a larger size. The values in the chart apply to normal 50/60 Hz installations.
A: Not at the same voltage. DC and single-phase AC both use the 2× round-trip voltage-drop rule, and DC has no power factor or reactance, so at the same amps and voltage the DC conductor is rarely bigger. The reason DC circuits look so much thicker is low voltage: a 12 V circuit has a tiny drop budget, 3% of 12 V is just 0.36 V, so a long run needs very thick copper, while the same amps at 240 V AC has 7.2 V of budget to spend. Use the general electrical wire size calculator for DC runs, and this page for AC.
A: A 100 kW generator at 400 V three-phase produces about 180 A of AC output current. Applying the 125% continuous-load factor, the output cable is 95 mm² copper (≈ 3/0 AWG) for a normal run. A long run, or a generator placed far from the building, needs a size confirmed against your exact distance, so run it through the calculator.
