# Introduction

Source: https://meptools.com/tools/voltage-drop-cable-checker/docs/introduction/

**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:

1. **Protective-device coordination** — design current, device rating, and cable current
   capacity are related as Ib ≤ In ≤ Iz.
2. **Current-carrying capacity** — the cable's tabulated capacity, corrected for the
   installation conditions you set, against the protective device rating.
3. **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](/tools/voltage-drop-cable-checker/docs/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](/tools/voltage-drop-cable-checker/docs/getting-started) — run a first
  check with the tool's default inputs.
- [Method and formulas](/tools/voltage-drop-cable-checker/docs/method) — every equation
  behind the reported figures.
- [Limits and what is not checked](/tools/voltage-drop-cable-checker/docs/limits-and-assumptions) —
  the exact scope boundary of the checks.