Voltage Drop Calculator: Optimize Electrical Systems for DC and AC Circuits

How to use the tool

1 Select the system type

Pick DC, Single-phase AC, or Three-phase AC. Example inputs:
• 24 V DC solar string
• 400 V three-phase pump

2 Choose conductor material

Copper (lower resistance) or Aluminum (lighter, cheaper). Example: compare 10 m copper vs 150 m aluminum.

3 Set wire size (AWG)

Select from the list or match your design tables. Example sizes:
• AWG 10 for rooftop array
• AWG 8 for long industrial feeder

4 Enter conductor length

Total one-way run in metres; the tool internally uses the same value entered.

5 Enter load current

Amperes flowing through the conductor.

6 Supply voltage

Nominal line voltage.

7 Optional AC fields

Power factor (0–1) and Frequency (Hz).

Underlying formulas

• Resistive drop $$V_{DC}=I R$$
• Resistance $$R=rac{\rho L}{A}$$
• Inductive reactance $$X=2\pi f L_s L$$ (with (L_s)=0.5 µH m⁻¹)
• Single-phase AC $$V_{1\phi}=2I(R\cos\phi+X\sin\phi)$$
• Three-phase AC $$V_{3\phi}=\sqrt3 I(R\cos\phi+X\sin\phi)$$
• Percentage drop $$\%V=rac{V_{drop}}{V_{supply}}\times100$$

Worked examples

Example A 24 V DC array

• Material: copper ρ = 1.68 × 10⁻⁸ Ω·m
• AWG 10 A = 5.26 mm²
• L = 10 m I = 18 A
• R = 0.032 Ω V_drop = 0.58 V
• %V = 2.4 % (compliant)

Example B 400 V 3-phase feeder

• Material: aluminum ρ = 2.82 × 10⁻⁸ Ω·m
• AWG 8 A = 8.36 mm²
• L = 150 m I = 60 A f = 50 Hz PF = 0.82
• R = 0.505 Ω X = 0.024 Ω
• V_drop = 44.5 V %V = 11.1 % (non-compliant)

Quick-Facts

• NEC advises ≤3 % drop on branch circuits and ≤5 % overall (NEC 210.19, 2023).
• Copper resistivity 1.68 × 10⁻⁸ Ω·m @ 20 °C (ASM Handbook, 2017).
• Aluminum resistivity 2.82 × 10⁻⁸ Ω·m @ 20 °C (IEEE Std 141, 2010).
• IEC 60364 allows ≤5 % drop for most installations (IEC 60364-5-52, 2020).
• Copper averages US$8–10 kg; aluminum US$2–3 kg (LME Price Report, 2023).

FAQ

Why is voltage drop limited to 3–5 %?

Excess drop wastes energy and may starve loads; NEC 210.19 and IEC 60364 cap it at 3 % for lighting and 5 % otherwise (NEC 2023; IEC 2020).

How does wire size affect drop?

Larger cross-section lowers resistance rac{1}{A}; doubling area halves drop (ASM Handbook, 2017).

When should I upsize conductors?

If the tool shows >5 % loss, select the next AWG size or switch to copper to meet code limits (NEC 2023).

Does temperature change results?

Yes; resistance rises ~0.4 % / °C for copper above 20 °C (IEEE Std 1202, 2019). Adjust design for hot environments.

Is reactance important on short runs?

Below 30 m the X term contributes <1 % of total drop at 50/60 Hz, so resistance dominates (IEEE Red Book, 2010).

Can I use the calculator for 12 V automotive wiring?

Yes—select DC, input 12 V supply, and check that drop stays under 0.5 V for critical circuits (SAE J1292, 2018).

What about renewable systems?

PV arrays tolerate up to 3 % loss to maximise inverter efficiency (NREL Best Practices, 2022).

How does power factor influence AC drop?

Lower PF raises the reactive term: “Under inductive loads voltage drop increases in proportion to sin φ” (IEC 60364, 2020).