Voltage Regulation Calculator
Calculate voltage drop, drop percentage, and receiving-end voltage for power cables with resistance and reactance.
Inputs
A
m
Ω/km
Ω/km
V
Results
Voltage Drop
9.68 V
Voltage Drop
2.02%
Receiving End Voltage470.32 V
≤3% Drop?1 (1=yes, 0=no)
How to Use This Calculator
- Enter the Load Current in amperes and the Cable Length (one way) in meters from source to load.
- Enter the Cable Resistance in Ω/km from the manufacturer datasheet or NEC Chapter 9 Table 9 — e.g., 95 mm² copper ≈ 0.193 Ω/km.
- Enter the Cable Reactance in Ω/km — typically 0.06–0.10 Ω/km for cables in conduit.
- Enter the Load Power Factor and Source Voltage in volts.
- Read the Voltage Drop in volts and as a percentage — NEC recommends a maximum of 3% for branch circuits and 5% total (feeder + branch).
- If the drop exceeds 3%, increase cable size, reduce run length, or raise source voltage to bring the load within specification.
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