Electrical Load Schedule Builder
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Open ToolCable Sizing & Voltage Drop Planner
Cable size calculator and voltage drop checker for NEC, IEC, BS 7671, and GCC planning profiles. Estimate load current, voltage drop, and ampacity margin before detailed design.
What is a cable sizing and voltage drop calculator?
A cable sizing and voltage drop calculator checks whether a selected cable size is likely to carry the load current and stay within a voltage drop limit. It uses load, voltage, phase, power factor, route length, conductor material, and cable size to estimate current, ampacity margin, and voltage drop. Engineers use it during concept design, tender review, site changes, and quick coordination when a feeder or branch circuit needs a sanity check. The selected standard profile can adjust planning limits such as voltage drop or ampacity margin. The result is not a final cable schedule. Final cable selection must also consider installation method, grouping, ambient temperature, insulation type, fault level, protective device coordination, earthing, local code tables, and approved project specifications. For best results, keep the entered units consistent, load the sample first, then adjust one assumption at a time so the result can be reviewed and explained.
Inputs
Forms are empty on load. Use sample data to preview the workflow or enter your own project values.
Video tutorial
Watch a quick walkthrough with sample inputs, calculation flow, and result interpretation.
Open the Cable Sizing & Voltage Drop Planner tutorial on YouTube
Learn more
Formula logic, use cases, assumptions, and limits for this tool.
How this tool helps
Use this for cable-size planning and voltage-drop checks. Final cable selection must consider installation method, ambient temperature, grouping, insulation type, fault level, and local code.
Assumptions and limits
This tool provides a planning-level result. It does not replace detailed engineering design, approved software, manufacturer data, authority requirements, or project specifications.
Typical use cases
- Early estimation and tender support.
- BOQ sanity checking and technical review.
- Site discussion before final engineering verification.
- Comparison of alternatives using consistent assumptions.
Result interpretation
Read the recommendation, warning, and confidence sections together. A result without warnings is still not an approval; it only means the entered values did not trigger built-in planning alerts.
Input definitions and typical values
These notes explain what each input means and which values usually produce a more reliable planning result.
Code / standard profile
Selects the planning profile used for conservative defaults. Use the project authority or client standard where known; otherwise use the closest regional profile. Options: GCC project planning, NEC planning, IEC planning, BS 7671 planning.
Load kW
Electrical or thermal load used by the calculation. Use demand/running load when sizing operating capacity and connected load for schedules.
Voltage V
System voltage. Common LV systems include 230 V single-phase and 400/415 V three-phase; use project nominal voltage.
Phase
Electrical phase arrangement. Use single-phase for small loads and three-phase for larger balanced motors, panels, and feeders.
Power factor
Power factor. 0.8-0.95 is common for many loads; motors and mixed loads should use measured or specified PF.
One-way cable length m
Measured length of the route, room, pipe, duct, or cable run. Use the actual equivalent length including bends, fittings, or route offsets where applicable.
Conductor material
Conductor or pipe material. Copper and aluminum have different resistance/ampacity; pipe materials have different internal bores.
Selected cable size mm2
Selected cable or equipment size. Use the actual proposed size to check margin and warning status.
Maximum voltage drop %
Maximum allowed voltage drop. Common planning targets are 3-5%, but final limits depend on circuit type and local standard.
Practical verification checklist
- Confirm the selected standard profile is suitable for the project location and authority.
- Replace sample values with project drawings, schedules, equipment data, or measured site values.
- Review warnings, methodology, and PDF report before using the result outside early planning.
- Verify final decisions against official standards, manufacturer data, consultant specifications, and local approvals.
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Open ToolCalculation methodology
Current is calculated from kW, voltage, phase, and power factor. Voltage drop uses conductor resistance, route length, and selected cable size.
Inputs are treated as planning assumptions. The calculator shows warnings when entered values fall outside practical thresholds or selected standard-profile limits.
Version history
- v1.3.6-prelaunch: Added methodology, standard profile support, version notes, and direct PDF report download.
- v1.3.5: Calculator page added with sample data, warnings, and print-ready report layout.
Stage 2 roadmap: optional saved projects, dashboards, and shared calculation history without forcing login for free use.
Trust and verification
Every result includes assumptions, warning logic, and a downloadable report. Final engineering decisions still need qualified review, local authority approval, manufacturer data, and project specifications.
Worked example
Use the sample data button to load a realistic scenario, then download the PDF report to review inputs, results, methodology, warnings, and disclaimers in one place.