DC Voltage Drop Calculator
Calculate voltage drop in a DC cable run based on current, cable length and cable resistance.
voltage drop
DC
cable
wiring
24V
48V
Input values
⚙
Enter values and click Calculate to see results here.
Formula
V_drop = (2 × L × I × R) / 1000
Worked Example
Given: A 24 V DC supply feeds a sensor 80 m away. The sensor draws 0.5 A. The cable resistance is 3.6 Ω/km.
Step 1: V_drop = (2 × 80 × 0.5 × 3.6) / 1000 = 0.288 V
Step 2: % drop = (0.288 / 24) × 100 = 1.2%
The cable is suitable — voltage drop is within the typical 3–5% limit.
Engineering Notes
- Why multiply by 2? Current flows out on the positive conductor and returns on the negative. Both conductors contribute to voltage drop.
- Practical limit: Most 24 V DC systems tolerate a maximum of 5% drop. For sensitive sensors, keep it below 2%.
- Cable resistance: Check the cable datasheet. Common values: 0.5 mm² ≈ 36 Ω/km, 1.0 mm² ≈ 18 Ω/km, 2.5 mm² ≈ 7.4 Ω/km.
- PLC analog inputs: If the voltage at the sensor drops below the minimum, the PLC may read an incorrect value. Always calculate before installation.
References
- IEC 60364-5-52 — Selection of conductors
- NEC Chapter 9, Table 8 — Conductor properties