Wire & Cable ReferenceUpdated 2026-08-15
Understanding Voltage Drop: Formulas, Consequences & Mitigation
Learn what causes voltage drop in electrical wiring, how to calculate resistance losses over long distances, code recommendations, and how to prevent brownouts.
Key Formulas: ΔV = 2 × I × R_one_way (1-Phase/DC) | ΔV = √3 × I × R_one_way (3-Phase)
What Causes Voltage Drop?
Every electrical conductor exhibits natural resistance to the flow of electric current according to its material resistivity (), length (), and cross-sectional area ():
When current () passes through this resistance, a portion of the source potential difference is dropped across the wire rather than the load (), resulting in reduced voltage delivered to equipment.
Consequences of Excessive Voltage Drop
•
Induction Motors: Voltage drops below 10% cause motors to draw significantly higher running current, resulting in severe winding overheating, torque loss (), and premature failure.
•
Electronic Power Supplies & Inverters: Low input voltage forces switching power supplies to draw higher current or trip on under-voltage lockout.
•
Incandescent & LED Lighting: Output lumens drop noticeably; LED drivers may flicker.
•
Heaters: Resistive heat output drops with the square of voltage ().
Practical Methods to Mitigate Voltage Drop
1
Upsize the Conductor: Increasing cross-sectional area () directly reduces resistance.
2
Increase the System Voltage: Transmitting power at 240V, 480V, or higher reduces current for the same wattage, reducing voltage drop dramatically ().
3
Center the Distribution Subpanel: Shorten circuit runs by locating breaker subpanels closer to heavy loads.
Frequently Asked Questions
Is voltage drop dangerous?
Yes. Excessive voltage drop can cause motors to overheat and burn out, produce excessive heating along the length of the cable, and cause safety systems or computers to reset unexpectedly.