AWG 12 voltage drop calculator
Voltage drop is current times the resistance of the round trip. For AWG 12 the resistance comes straight from the gauge definition and the conductor resistivity.
A
V
Voltage drop
2.718%
- Voltage lost in the cable
- 6.2525 V
- Voltage at the load
- 223.748 V
- Power lost as heat
- 125.05
- Resistance per metre
- 0.005 210 39 ohm/m
- Conductor area
- 3.308 77 mm2
- Longest run within 3% drop
- 33.11
Show the working
- Current = 20
- One-way run length = 30
- Supply voltage = 230
- System = 2
- Conductor = 1.724e-8
- Conductor temperature = 20
- diameter_mm = 0.127 * 92^((36 - (12)) / 39) = 2.052 53
- Conductor area = pi * 2.052 53^2 / 4 = 3.308 77
- Resistance per metre = 1.724e-8 / (3.308 77 * 1e-6) * (1 + 0.00393 * (20 - 20)) = 0.005 210 39
- Voltage lost in the cable = 2 * 20 * 0.005 210 39 * 30 = 6.252 47
- Voltage drop = 6.252 47 / 230 * 100 = 2.718 46
- Voltage at the load = 230 - 6.252 47 = 223.748
- Power lost as heat = 6.252 47 * 20 = 125.049
- Longest run within 3% drop = 0.005 210 39 > 0 && 20 > 0 ? 230 * 0.03 / (2 * 20 * 0.005 210 39) : 0 = 33.1069
Values are shown to six significant figures here; the arithmetic itself runs on exact fractions and is only rounded where a number is printed.
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The formula
- single phase or DC: drop = 2 x I x R per metre x one-way length
- three phase: drop = sqrt(3) x I x R per metre x one-way length
- R per metre = rho / area, corrected for temperature
The factor of two on a single-phase run is because the current goes out and comes back. A three-phase drop uses sqrt(3) because the return currents partly cancel.
This is resistive drop only. On long AC runs at high current, cable reactance adds to it.
Warm conductors have more resistance: at 70 degrees Celsius copper is about 20% more resistive than at 20.