AWG 4 voltage drop calculator
Voltage drop is current times the resistance of the round trip. For AWG 4 the resistance comes straight from the gauge definition and the conductor resistivity.
A
V
Voltage drop
0.425%
- Voltage lost in the cable
- 0.9781 V
- Voltage at the load
- 229.022 V
- Power lost as heat
- 19.56
- Resistance per metre
- 0.000 815 105 ohm/m
- Conductor area
- 21.1506 mm2
- Longest run within 3% drop
- 211.63
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 - (4)) / 39) = 5.1894
- Conductor area = pi * 5.1894^2 / 4 = 21.1506
- Resistance per metre = 1.724e-8 / (21.1506 * 1e-6) * (1 + 0.00393 * (20 - 20)) = 0.000 815 105
- Voltage lost in the cable = 2 * 20 * 0.000 815 105 * 30 = 0.978 126
- Voltage drop = 0.978 126 / 230 * 100 = 0.425 272
- Voltage at the load = 230 - 0.978 126 = 229.022
- Power lost as heat = 0.978 126 * 20 = 19.5625
- Longest run within 3% drop = 0.000 815 105 > 0 && 20 > 0 ? 230 * 0.03 / (2 * 20 * 0.000 815 105) : 0 = 211.629
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.