AWG 7 voltage drop calculator
Voltage drop is current times the resistance of the round trip. For AWG 7 the resistance comes straight from the gauge definition and the conductor resistivity.
A
V
Voltage drop
0.853%
- Voltage lost in the cable
- 1.9612 V
- Voltage at the load
- 228.039 V
- Power lost as heat
- 39.22
- Resistance per metre
- 0.001 634 31 ohm/m
- Conductor area
- 10.5488 mm2
- Longest run within 3% drop
- 105.55
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 - (7)) / 39) = 3.664 85
- Conductor area = pi * 3.664 85^2 / 4 = 10.5488
- Resistance per metre = 1.724e-8 / (10.5488 * 1e-6) * (1 + 0.00393 * (20 - 20)) = 0.001 634 31
- Voltage lost in the cable = 2 * 20 * 0.001 634 31 * 30 = 1.961 17
- Voltage drop = 1.961 17 / 230 * 100 = 0.852 685
- Voltage at the load = 230 - 1.961 17 = 228.039
- Power lost as heat = 1.961 17 * 20 = 39.2235
- Longest run within 3% drop = 0.001 634 31 > 0 && 20 > 0 ? 230 * 0.03 / (2 * 20 * 0.001 634 31) : 0 = 105.549
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.