# Reading the result

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

The result panel is empty until you press **Calculate** (or **Load a worked example**, which
runs immediately) — it does not recompute as you type. Once a result is showing, editing any
input flips the action rail from **Calculated** to **Recalculate** and shows a strip: "Inputs
changed. You're looking at **the previous run**." — everything below still reflects that
previous run until you press **Recalculate**. See
[Getting started](/tools/voltage-drop-cable-checker/docs/getting-started) for the full
calculate/recalculate cycle.

## The headline

The hero figure is **Voltage drop**, the calculated drop as a percentage of nominal voltage,
shown to two decimal places. Beneath it a badge reads **PASSES** or **FAILS** against your
selected voltage-drop limit (the Allowable VD % set in stage 01). Below that:

- **`<VD> V drop · receiving end <Vr> V`** — the drop restated in volts, and the resulting
  receiving-end voltage.
- A **meter** plotting your voltage-drop percentage against the allowable percentage, with the
  limit labelled at the right-hand end and a marker showing where your result falls.

## The three checks

Below the headline, three checks are shown side by side:

| Check                   | What it reports                                                                                                              |
| ----------------------- | ---------------------------------------------------------------------------------------------------------------------------- |
| **Device coordination** | PASS or FAILS — whether the design current, device rating, and cable capacity satisfy Ib ≤ In ≤ Iz.                          |
| **Current capacity**    | PASS or FAILS, with the corrected Iz per run in amps — the cable's tabulated ampacity after installation correction factors. |
| **Voltage drop**        | PASS or FAILS, with the voltage-drop percentage again.                                                                       |

The overall result (the colour of the whole readout) passes only if **all three** checks pass.
A single failing check fails the overall result even if the other two pass.

## Metrics

A row of four metric tiles beneath the checks:

| Metric                   | Unit   | Meaning                                                                                                                  |
| ------------------------ | ------ | ------------------------------------------------------------------------------------------------------------------------ |
| **Design current / run** | A      | The design current per parallel run (Ib), after dividing by the number of parallel runs.                                 |
| **Corrected Iz / run**   | A      | The tabulated current-carrying capacity after installation correction factors, per parallel run.                         |
| **Coefficient**          | mV/A/m | The voltage-drop coefficient used for the calculation — from the BS 7671 table, or your manufacturer override if active. |
| **Max length**           | m      | The longest one-way run length that would still pass the voltage-drop check at these currents and this coefficient.      |

## Cable size comparison

The **Cable size comparison** table lists every compatible cable size in the selected
family/installation-method/circuit combination, with one row per size:

| Column           | Meaning                                                                 |
| ---------------- | ----------------------------------------------------------------------- |
| **Size**         | Cable size, mm².                                                        |
| **Table Iz**     | The tabulated (uncorrected) ampacity for that size.                     |
| **Corrected Iz** | Table Iz after installation correction factors.                         |
| **mV/A/m**       | The voltage-drop coefficient for that size.                             |
| **VD (V)**       | Calculated voltage drop in volts at your current and length.            |
| **VD %**         | Calculated voltage drop as a percentage of nominal voltage.             |
| **L max**        | The longest run length that size could carry within the allowable VD %. |
| **Status**       | See below.                                                              |

Status values:

| Status                     | Meaning                                                                           |
| -------------------------- | --------------------------------------------------------------------------------- |
| **AMPACITY FAIL**          | Corrected Iz is below the device rating for that size.                            |
| **VD FAIL**                | Ampacity passes but the voltage-drop percentage exceeds your allowable VD %.      |
| **SELECTED · SMALLEST OK** | This is both the size you selected and the smallest size that passes both checks. |
| **SMALLEST OK**            | The smallest size that passes both checks, but not the one currently selected.    |
| **SELECTED**               | The size you selected, passing both checks, but not the smallest that does.       |
| **PASS**                   | Passes both checks; neither selected nor the smallest passing size.               |

The tool always identifies the smallest compatible size where both the current-capacity and
voltage-drop checks pass, regardless of which size you have selected. To keep the table
manageable, only a window of rows around the selected and smallest-passing sizes is shown
initially; a **Show all N compatible sizes** button reveals the full list.

The comparison is only available when the coefficient comes from the **BS table** — if a
manufacturer coefficient override is active, the comparison is hidden because that coefficient
applies only to the single selected cable. See
[Cable and installation selection](/tools/voltage-drop-cable-checker/docs/cable-and-installation)
for the manufacturer override.

## Formula steps

The **Calculation steps** panel (open by default) is a full audit trail: for every step —
design current, device coordination (Ib ≤ In ≤ Iz), each correction factor applied, required/
selected/corrected capacity, the voltage-drop coefficient, the voltage-drop limit, the
calculated VD and VD%, the receiving voltage, and the maximum length — it shows the symbolic
formula, the substituted values, and the numeric result, with a source-table reference where
one applies.

When the comparison table is available, a final **Minimum-size evaluation** step is appended,
stating how many compatible sizes were evaluated and which is the smallest suitable size (or
that none passes).

See [Method and formulas](/tools/voltage-drop-cable-checker/docs/method) for the equation
behind each audit step.

## Assumptions and warnings

The collapsible **Assumptions and warnings** panel lists:

- Any run-specific warnings raised by your inputs (for example, a manufacturer-override
  notice, or a note tied to the selected installation/arrangement).
- **"Pass means the implemented checks pass under the stated inputs. It is not a declaration
  of full BS 7671 compliance."**
- **"Displayed values are rounded to two decimal places for readability. Calculations use
  full unrounded precision internally."**

These two notes are always shown, independent of your inputs.