Getting started — MEP Tools
Load the worked example or enter your own circuit, press Calculate, and read the result.
Open Voltage Drop & Cable Size Checker from the tools catalog. No sign-in is needed to calculate — you only need an account to save projects or export a PDF report.
The page is a single column: three input stages (01 Circuit & load, 02 Cable selection, 03 Installation corrections) with the result panel beneath them. The tool opens blank — nothing is pre-filled, and nothing calculates automatically as you type. You fill in the stages (or load the worked example below), then press Calculate.
Before you calculate
With no result yet, the result panel shows a start zone:
Your result appears here
A pass/fail verdict, the smallest size that works, a size-by-size comparison and every formula step — produced from the inputs below when you press Calculate.
- Enter the circuit 2. Calculate 3. Save it — free account
Load a worked example Fills a typical 400 V submain and runs it. Nothing is saved until you say so.
Load the worked example
Press Load a worked example to fill both stages with a preset circuit and run it immediately — you don't press Calculate separately; loading the example calculates it.
01 Circuit & load
| Field | Value |
|---|---|
| Circuit type | 3-ph AC |
| Nominal voltage | 400 V |
| Voltage-drop limit | Custom / project specification |
| Custom limit | 5 % |
| Protective device type | MCB - BS EN 60898 |
| Protective device rating | 80 A |
| Load | 45 kW |
| Power factor (lagging) | 0.85 |
| Parallel runs | 1 |
| Run length | 65 m |
02 Cable selection
| Field | Value |
|---|---|
| Cable construction | 4E4 (multicore XLPE armoured) |
| Installation method | Clipped direct, reference method C |
| Circuit arrangement | 3ph |
| Cable size | 35 mm² |
| Ambient temperature | 30 °C |
| Grouping | 1 circuit |
| Thermal insulation | Not in insulation |
| Manufacturer override | Off — the tabulated BS voltage-drop coefficient is used |
Once it loads, the action rail shows Calculated and an EXAMPLE badge appears next to the Result heading — this is a real, already-run calculation, not a placeholder.
Reading the result
For the worked example above, the result panel shows:
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Voltage drop 1.30 %, badge PASSES — 5.21 V drop, receiving end 394.79 V.
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Three checks, all PASS: Device coordination (76.41 A ≤ 80.00 A), Current capacity (80.00 A ≤ 154.00 A), Voltage drop (1.30 % ≤ 5.00 %).
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Four metric tiles: Design current / run 76.41 A, Corrected Iz / run 154.00 A, Coefficient 1.049 mV/A/m, Max length 249.60 m.
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A recommendation: "35 mm² also passes — you are 2 sizes oversized. It gives 1.30 % against your 5 % limit."
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A Length headroom bar (65 m of 249.60 m max — 26 % used) and a Size ladder of clickable size chips — picking one recalculates the whole result against that size.
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Cable size comparison — "17 sizes evaluated · smallest suitable 16 mm²", with per-row statuses (AMPACITY FAIL, SMALLEST OK, SELECTED, PASS, and so on) and a Show all 17 compatible sizes button that reveals every row.
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Calculation steps — an "11 steps" audit trail, with a Summary / Full audit trail toggle.
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Assumptions and warnings — a collapsible panel of any run-specific notes plus the standing disclaimers.
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A Report section offering Print / Save as PDF and Export branded PDF (the latter carries a PRO badge on free accounts).
Editing after a calculation
Change any input once a result is showing, and the action rail switches from Calculated to Recalculate — the figures on screen do not update yet. A strip above the result reads "Inputs changed. You're looking at the previous run." until you press Recalculate.
Then
- Circuit & load inputs — every field in stage 01, in detail.
- Cable & installation selection — cable families, installation methods, and the manufacturer override.
- Correction factors — how the installation corrections adjust the tabulated current capacity.
- Reading the results — the result panel, the comparison table, and the formula audit in full.
- Exporting and saving — PDF export and project save/load.