Size LV cables and verify voltage drop using BS 7671 data or custom impedance values—with formulas, source tables, and calculation assumptions clearly shown.
Voltage Drop & Cable Size Checker (ELC-01) checks a copper cable, selected from the
supported BS 7671 Appendix 4 cable families and installation methods, against three
implemented checks and finds the smallest compatible size that passes them.
What it evaluates
For the circuit and cable you configure, the tool runs three checks:
Protective-device coordination — design current, device rating, and cable current
capacity are related as Ib ≤ In ≤ Iz.
Current-carrying capacity — the cable's tabulated capacity, corrected for the
installation conditions you set, against the protective device rating.
Voltage drop — the calculated drop along the run against your selected voltage-drop
limit.
It also searches the compatible cable sizes in the selected family/method/circuit
combination and identifies the smallest one that passes both the current-capacity and
voltage-drop checks, so you can see at a glance whether a smaller (cheaper) conductor is
viable.
Every result is backed by a full formula-by-formula audit trail — the symbolic formula, the
substituted values, and the numeric result for each step — plus references to the source
tables used, so the calculation can be checked line by line.
Manufacturer override
The tabulated voltage-drop coefficient (mV/A/m) that BS 7671 Appendix 4 assigns to the
selected cable can be replaced with manufacturer data — either a resistance (R) and
reactance (X) pair or a direct mV/A/m value. The tabulated current-capacity check is
retained regardless of which voltage-drop coefficient source is active, so overriding the
voltage-drop figure never bypasses the ampacity check.
Layout
The tool is a single screen:
A header showing the tool name and a one-line method summary.
Three input stages: 01 Circuit & load (circuit type, voltage, protective device, load,
power factor, parallel runs, run length), 02 Cable selection (cable construction,
installation method, circuit arrangement, size, and the manufacturer override), and
03 Installation corrections (ambient temperature, grouping, thermal insulation, and the
buried-cable factors when the method is buried).
A result panel showing the voltage-drop figure, the three check statuses, key metrics, the
cable-size comparison table, and the formula audit — once you've run a calculation.
The tool opens blank and nothing calculates automatically as you type. You fill in the
input stages — or press Load a worked example to start from a filled-in circuit — and press
Calculate to run it. Editing an input afterward does not update the figures live: the
action rail switches to Recalculate and a strip marks the displayed result as the previous
run until you press it again. See
Getting started for the full
calculate/recalculate flow.
Disclaimer
The tool displays, verbatim:
For engineering guidance and checking only. Final cable selection must be verified by
a qualified professional using the applicable code edition, local amendments,
manufacturer data, and authority requirements.
What it does not do
Replace a full cable design workflow.
Perform short-circuit or disconnection-time (Zs) checks.
Check discrimination/selectivity between protective devices.
Substitute for manufacturer verification of the selected cable.
Confirm project-specific requirements or local-authority approval.
Next
Getting started — run a first
check with the tool's default inputs.