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What is Voltage Drop?
Voltage drop is the reduction in voltage in an electrical circuit between the source and the load. It occurs because conductors have resistance (and reactance) that consume a small portion of the supplied voltage as current flows. Excessive voltage drop can result in poor equipment performance, overheating, and reduced lifespan of motors and electronics.
Formula Used by the Calculator
This calculator estimates voltage drop using a simple resistance-based approximation:
- Convert conductor resistance from ohm/km to ohm per conductor length: Rtotal=Rkm×L×21000R_{total} = \frac{R_{km} \times L \times 2}{1000}Rtotal=1000Rkm×L×2 where RkmR_{km}Rkm is resistance in ohm/km and LLL is one-way cable length in meters. The factor 2 accounts for the return path.
- Then the estimated voltage drop is: ΔV=k×I×Rtotal\Delta V = k \times I \times R_{total}ΔV=k×I×Rtotal where:
- III = load current (A)
- kkk = system multiplier (1 for single-phase, 3≈1.732\sqrt{3}\approx1.7323≈1.732 for three-phase line-to-line calculations)
This method provides a quick rule-of-thumb estimate. For AC systems with significant reactance, or where accuracy is critical, include cable reactance (X) and use complex phasor calculations.
Typical Acceptable Limits
Design practice usually limits voltage drop to preserve equipment performance:
- Lighting and general circuits: typically 3%–5% of nominal voltage.
- Motors and sensitive equipment: keep below 3% where possible.
Check applicable national or local codes for exact limits.
Practical Applications
- Cable sizing checks: verify that cable runs are adequate for load and distance.
- Motor starting and performance: ensure motors receive sufficient voltage at full load.
- Renewable systems and long runs: in solar or remote installations, voltage drop is a major design constraint.
- Lighting and control circuits: prevent flicker or misoperation of sensitive electronics.
How to Improve Voltage Drop / Mitigate Issues
- Increase conductor cross-sectional area (use larger cable sizes).
- Reduce run length or relocate equipment nearer to the supply.
- Use higher system voltage where practical (reduces current for same power).
- Balance loads on three-phase systems to reduce neutral currents.
- Consider voltage regulators or local transformers for long-distance supplies.
Important Notes and Limitations
- This calculator uses conductor resistance only; it does not include reactive impedance (inductive reactance). For long AC cable runs, especially at higher currents or with long motor feeders, include reactance and perform a full complex impedance calculation.
- Always verify final designs against manufacturer recommendations and local electrical codes (IEC, NEC, IS, etc.). For critical or large power installations, consult a qualified electrical engineer.
