Why Parallel Voltage Drop Matters
In a parallel circuit, each branch connects across the same bus. Ideally, each load receives the same voltage. Real circuits are different. Wires, terminals, fuses, and source resistance add series resistance. Current through those parts creates voltage loss. This lowers the bus voltage. Each branch can also lose voltage in its own lead wire.
A small drop may be harmless. A large drop can heat wires and reduce equipment performance. Motors may start slowly. Lamps may dim. Control boards may reset. Sensitive sensors may read incorrectly. This calculator models those effects with an ohm based method.
What This Tool Checks
The calculator accepts source voltage, source resistance, feeder resistance, and branch data. Each branch uses load resistance and branch wire resistance. It then finds total conductance, equivalent branch resistance, total current, feeder drop, branch current, load voltage, and power loss.
The result is useful for low voltage panels, lighting runs, test benches, battery circuits, and training examples. It also helps compare branches. You can see which branch has the worst loaded voltage. You can also check current sharing and total wasted power.
Design Notes
Use measured resistance when possible. Long conductors should include the outgoing and returning path. Loose terminals should be fixed before final design. Temperature can raise resistance. Safety codes may require lower limits for certain equipment.
This calculator is a planning aid. It does not replace testing. It also does not size breakers or confirm insulation ratings. Use it with accepted electrical rules and local requirements.
Better Inputs Give Better Results
Enter realistic load resistance values. For rated devices, convert voltage and power to resistance with R = V² / P. Use the expected operating voltage. For mixed branches, enter each load separately. Include branch lead resistance when the load sits far from the bus.
The percentage limit helps flag weak designs. A common target is three percent for many branch circuits. Some electronics need tighter limits. Battery systems may allow different limits. Review the worst branch, not only the average.
Good voltage drop work protects performance and reliability. It also reduces wasted heat. When currents are high, small resistances matter. Good layout, larger conductors, tight joints, and balanced branches often improve the result.