Aluminum AWG comparison
How do you calculate voltage drop?
Every metallic conductor has internal electrical resistance. As current flows through a run of copper or aluminum wire, part of the source voltage is lost as heat along the cable path. Using Ohm's law (V = I × R) and circular-mil resistivity at 75°C, the voltage lost across a two-wire circuit is:
where:
- VD – Total voltage drop between the supply panel and the load terminals, measured in volts (need a target gauge instead? Use the wire size calculator);
- K – Conductor resistance constant at 75°C (K = 12.9 for copper and K = 21.2 for aluminum in Ω·CM/ft);
- I – Load current flowing through the circuit in amps (estimate from wattage with our watts to amps calculator);
- L – One-way wire distance in feet (the multiplier of 2 already accounts for the return conductor); and
- CM – Conductor cross-sectional area in circular mils from NEC Chapter 9, Table 8.
Three-phase AC voltage drop equation
In a balanced three-phase system, the return currents cancel in phase opposition, so the round-trip factor of 2 is replaced by √3:
Subtract VD from the source voltage (V_load = V_source − VD) to find the actual voltage delivered to the equipment terminals. Explore all related tools in our electrical calculators hub.
| Aluminum AWG | Estimated volts lost | Estimated percentage |
|---|---|---|
| 14 | 30.95 V | 12.90% |
| 12 | 19.48 V | 8.12% |
| 10 | 12.25 V | 5.11% |
| 8 | 7.70 V | 3.21% |
| 6 | 4.85 V | 2.02% |
| 4 | 3.05 V | 1.27% |
| 2 | 1.92 V | 0.80% |
Do not convert material by a fixed AWG rule
A statement such as 'move up two sizes' hides the actual load, distance, target, ampacity column and terminal conditions. Recalculate area and then verify the complete system.
A larger aluminum conductor can affect lug range, enclosure bending space, raceway fill and pulling. Compare installed-system requirements rather than price per foot alone.
Termination checklist
- 01
Read equipment markings
Confirm every lug and connector is identified for aluminum and the selected size.
- 02
Follow preparation instructions
Use the manufacturer-specified stripping, cleaning, compound and torque procedures.
- 03
Check physical fit
Verify raceway, bending space and enclosure capacity for the actual product.
- 04
Document material
Save the conductor alloy, insulation, AWG and termination products with the calculation.
What the chart does not show
- Permitted ampacity
- Terminal compatibility
- Conduit fill
- Parallel conductor rules
- Local inspection requirements
- Manufacturer-specific resistance and dimensions