Parallel Circuit Voltage Drop Calculator

Formula used

The calculator treats the branch loads as parallel resistance. It adds feeder resistance and source resistance before the parallel bus.

Parallel equivalent resistance: 1 / Req = 1 / R1 + 1 / R2 + 1 / R3 + ...

Feeder resistance: Rf = length × conductor resistance × path multiplier × temperature factor

Total current: It = Vs / (Req + Rf + Rs)

Bus voltage: Vbus = Vs − It × (Rf + Rs)

Branch current: Ib = Vbus / Rb

Voltage drop percent: Drop % = [(Vs − Vbus) / Vs] × 100

Load power: Pb = Vbus × Ib

How to use this calculator

1. Enter the supply voltage of the circuit.
2. Enter the one-way feeder length.
3. Enter conductor resistance per meter.
4. Use a path multiplier of 2 for common outgoing and return conductors.
5. Enter a temperature factor above 1 when wires run hot.
6. Add source internal resistance when known.
7. Enter each active branch resistance.
8. Leave unused branch fields as zero.
9. Press the calculate button.
10. Download the CSV or PDF when results are shown.

Example data table

About parallel circuit voltage drop

A parallel circuit gives each load the same bus voltage. In a perfect circuit, every branch receives the source voltage. Real wiring is different. Feeders, terminals, and internal source resistance add small resistance. Current passing through that resistance creates voltage drop before the branches.

Why this calculator helps

This calculator models that practical drop. It accepts source voltage, feeder length, conductor resistance, source resistance, and up to five branch loads. It then finds total current, feeder drop, bus voltage, branch current, load power, and estimated losses. The result helps you compare whether the circuit still delivers useful voltage.

Advanced electrical checks

Parallel circuits can hide overload problems. One low resistance branch can raise total current sharply. That higher current increases feeder loss for every branch. A small branch change can reduce bus voltage for all connected loads. The calculator shows this link in one place.

Design guidance

Use measured resistance when possible. Long cable runs should include the complete current path. For direct current, that is usually the outgoing and return conductor. For alternating current, simplified resistance estimates work for quick checks, but complex impedance may be needed for final design.

Interpreting results

A low voltage drop percentage is usually desirable. Sensitive electronics may need tighter limits than heaters or lamps. High feeder loss means wasted energy and extra heat. High branch current may indicate an undersized load resistance or a wrong entry. Always compare the output with local electrical rules and equipment ratings.

Practical tips

Enter branch resistance values in ohms. Leave unused branches blank or set them to zero. Add cable resistance per meter from a wire table or test meter. Use the temperature factor when conductors run hot. A factor above one increases resistance and drop. Download the CSV for records. Use the PDF button for a clean job note.

Safety note

This tool is an estimator. It does not replace code review, breaker sizing, conductor ampacity checks, or field testing. Use conservative values for resistance and current. Check terminals after installation. Warm joints can raise resistance and drop. Shut power off before measuring conductors. Ask a qualified electrician when circuits serve critical loads. Document final readings with date, load, and voltage.

FAQs