Branch circuit input form
Large screens show three columns, smaller screens show two, and mobile collapses to one.
Formula used
Rₘ = ρ₂₀ × [1 + α × (T - 20)] ÷ A
Vd single phase = 2 × I × L × (Rₘ × cosφ + Xₘ × sinφ)
Vd three phase = √3 × I × L × (Rₘ × cosφ + Xₘ × sinφ)
Vd DC = 2 × I × L × Rₘ
Drop % = (Vd ÷ Supply Voltage) × 100
Here, Rₘ is conductor resistance per meter, Xₘ is reactance per meter, I is design current, L is one-way length, and A is effective conductor area after parallel runs.
When resistance-only mode is selected, the reactance term is ignored. Power loss is based on resistive heating in the chosen branch path.
How to use this calculator
- Select the branch circuit type: single phase, three phase, or DC.
- Choose whether your known input is current or connected load power.
- Enter supply voltage, one-way length, power factor, and demand multiplier.
- Pick conductor material and size, or enter a custom cross-sectional area.
- Add temperature, parallel runs, reactance, and your target drop limit.
- Submit the form to view results, the comparison graph, and downloads.
Example data table
| Scenario | System | Voltage | Current | Length | Material | Size | Target |
|---|---|---|---|---|---|---|---|
| Lighting branch | Single phase AC | 230 V | 16 A | 22 m | Copper | 12 AWG | 3% |
| Tool outlet run | Single phase AC | 230 V | 28 A | 38 m | Copper | 8 AWG | 3% |
| Site pump feeder | Three phase AC | 400 V | 42 A | 55 m | Aluminum | 2 AWG | 5% |
| Temporary DC run | DC branch circuit | 48 V | 35 A | 18 m | Copper | 4 AWG | 3% |
Frequently asked questions
1) Why does one-way length matter so much?
Voltage drop increases directly with run length. Single-phase and DC circuits use the round-trip path, so long branches can lose voltage quickly even with moderate loads.
2) When should I use impedance instead of resistance only?
Use impedance mode for AC circuits when power factor and reactance matter, especially on longer runs or larger conductors. Resistance-only mode is a quick approximation.
3) What does the demand multiplier do?
It scales the base current to a design current. This helps model continuous loading, future allowance, or a site rule requiring margin above measured load.
4) Why does temperature affect the answer?
Conductor resistance rises as temperature increases. Hotter conductors create larger voltage drops, so temperature-adjusted resistance usually produces a more realistic field estimate.
5) Can I compare copper and aluminum fairly here?
Yes. The calculator changes resistivity and temperature coefficient by material. That lets you compare drop performance before finalizing conductor size and material choice.
6) What does the recommended listed size mean?
It is the first listed conductor size that meets your chosen target voltage drop under the same entered conditions. It is a design aid, not a code approval.
7) Does this replace electrical code checks?
No. This tool estimates branch voltage drop and loss. Final conductor sizing still needs code review, insulation checks, ampacity limits, and installation-specific constraints.
8) Why include a custom area option?
Custom area helps when you already know the exact conductor cross-section from a project schedule, manufacturer data sheet, or a nonstandard metric design.