Voltage Drop Calculator
Calculate voltage drop across a wire or cable.
This tool is for informational and educational purposes only. It is not a substitute for professional financial, medical, legal, or engineering advice. See Terms of Service.
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Enter the current, wire resistance per meter, one-way wire length, and supply voltage. The calculator computes the round-trip voltage drop, percentage, and voltage at the load end.
About Voltage Drop
Voltage drop in electrical wiring is caused by the resistance of the conductors. It is calculated as current times total wire resistance (accounting for both outgoing and return conductors). Excessive voltage drop wastes energy as heat and reduces voltage at the load. National electrical codes typically limit voltage drop to 3% for branch circuits and 5% total. Proper wire sizing is essential for electrical safety and efficiency.
Frequently Asked Questions
Why does voltage drop matter?
Excessive voltage drop means the load receives less voltage than intended, potentially causing equipment malfunction, dimming lights, or motor overheating. Most codes limit drop to 3-5%.
Why is the wire length doubled?
Current must flow to the load and return. A 50-meter run means 100 meters of total wire, doubling the resistance and voltage drop.
How can voltage drop be reduced?
Use thicker wire (lower resistance per meter), shorter runs, or higher supply voltage. For long runs, consider increasing wire gauge or using a higher distribution voltage.