Cable System
Every device with an outgoing cable (MCB, RCBO, AFDD, dimmer, fuse) can have its cable configured. ElectroBoard checks whether the cable is correctly sized against the breaker rating, and computes the corrected current-carrying capacity (ampacity) and the voltage drop.
Cable Parameters
In the device properties panel, the "Cable" section configures:
- Cross-section — the conductor cross-sectional area in mm²
- Conductor material — copper (Cu, default) or aluminium (Al)
- Insulation — PVC (70 °C operating temperature) or XLPE/EPR (cross-linked polyethylene, 90 °C)
- Number of cores — 3 (L+N+PE) for a single-phase circuit, 5 (L1+L2+L3+N+PE) for a three-phase one
- Installation method — how the cable is laid (affects the permissible current)
- Length — the distance from the panel to the load in metres (needed for the voltage-drop calculation)
- Ambient temperature and "Circuits in bundle" — ampacity correction factors (k1 and Cf). Circuits are counted, not cables: a multicore cable is one circuit; a whole number from 1 to 50
Standard Cross-Sections
The properties dropdown offers standard conductor cross-sections: 1.5, 2.5, 4, 6, 10, 16, 25, 35 mm². For the recommendation, the system computes ampacity across the full app reference table (up to 120 mm²). Choosing a non-standard cross-section shows an informational hint.
Typical uses:
| Cross-section | Typical use |
|---|---|
| 1.5 mm² | Lighting |
| 2.5 mm² | General-purpose sockets |
| 4 mm² | High-power loads (oven, hob up to 5 kW) |
| 6 mm² | Hob, electric boiler |
| 10 mm² | Feeder cable to an apartment panel |
| 16–35 mm² | Incoming cables, house connection |
Installation Methods
The installation method affects the cable's permissible current, because different cooling conditions change the thermal regime. These numbers are the app's reference table. ⚠️ Its source is unconfirmed: the method labels A2/B2/C/D1 and "3 loaded conductors" they were published under do not match the numbers.
| Method | Description | Ampacity (2.5 mm² Cu/PVC) |
|---|---|---|
| In a wall (chase) | Cable in a chase under plaster | 21 A |
| In conduit / duct | Cable in a corrugated conduit or duct | 24 A |
| On the surface | Cable clipped directly on the surface | 27 A |
| Underground | Cable in an earth trench | 29 A |
⚠️ The method changes the ampacity: the same 2.5 mm² cable carries a different current depending on how it is laid. In a wall chase it heats up more than when run in free air, so its permissible current is lower.
Default Method
A new cable gets the installation method "Surface". Cables inside the panel have a fixed method: the cable editor shows it as "Internal panel wiring" and it cannot be changed. For the remaining cables, the installation method is chosen in the cable editor.
Cabinet-internal cables (between devices on the same rail) always use "On the surface" and get their length automatically — see the input-cables section below.
Cable Protection Rule
The core coordination rule: the cable ampacity must be ≥ the rating of the breaker protecting it (IEC 60364-4-43 §433). The ampacity already accounts for the ambient-temperature and grouping correction factors.
Example: a 16 A breaker protecting a 2.5 mm² cable in a wall chase (21 A per the app reference table) is correct, because the breaker trips before the cable overheats. A cable whose permissible current is lower than the breaker rating is insufficient: on an overload it will reach a dangerous temperature before the protection trips.
ElectroBoard checks this rule automatically and flags any violation (see Automatic Checks).
Voltage Drop
As current flows through a cable, part of the voltage is "lost" across the conductor resistance. The longer the cable and the thinner the cross-section, the greater the drop.
Permissible limits:
- 3% or less — the norm for lighting
- 5% or less — the maximum permissible value for other circuits
ElectroBoard computes the voltage drop automatically as soon as the cable length is set, and warns when it is exceeded.
If the voltage drop is too high, increase the cable cross-section or reduce the circuit length (for example, move the junction box closer to the load).
💡 Three-phase lines: for 3P / 3P+N cables the calculation applies the √3 factor (line voltage 400 V):
ΔU% = √3 × I × L × ρ / (S × U_line) × 100. For single-phase lines:ΔU% = 2 × I × L × ρ / (S × U_phase) × 100(double the length — out and back over L and N). The phase count comes from the cable's core count: 3 cores → single-phase formula, 5 cores → three-phase.
ATS and Changeover Input Cables
Unlike ordinary devices with a single outgoing cable, an ATS (transfer switch) and a 1-0-1 changeover have two input cables:
- Main — the cable from the grid or the first source
- Reserve — the cable from a generator, UPS, or a second supply
Both are configured in the "Input cables" section of the ATS properties panel. The parameters are the same: cross-section, installation method, length. The system checks each cable independently per IEC 60364-5-52 — validation messages are tagged "main" / "reserve". Both are included in the bill of materials. The standard for transfer-switching equipment is IEC 60947-6-1.
💡 An ATS is not a protective device: an ATS and a changeover switch between sources but have no overcurrent-protection function, so their rating does not define the cable protection. The reserve cable (and the main one) has its cross-section checked against the rating of the real breaker found upstream (walking up through the ATS / contactor / relay). Both the validation top bar and the inline message in the device properties read this same effective rating, so they show identical recommendations for one cable.
Automatic Length for Internal Cables
Internal cables (between devices on the same rail, e.g. MCB → RCD → load) get their length automatically from the router's wire path, and their installation method is fixed to "On the surface" (internal panel wiring). This gives a more accurate voltage-drop calculation with no manual length entry.
External cables (to a load outside the panel) keep a manual length — the user enters the metres. You can switch the mode with the 📏 Auto / ✏️ Manual indicator next to the length field.
Voltage Drop for a Bonded Reserve
For an ATS with a bonding jumper (single-phase reserve supply feeding a three-phase load), the voltage-drop calculation on the reserve cable aggregates the current across all jumpers. A single conductor can carry the sum of the L1 + L2 + L3 currents when they collapse onto one phase — the formula accounts for this peak. Without it, the calculation would underestimate the real drop in the bonded-reserve mode.
Backfilling Input Cables for Existing ATSs
If your panel has an ATS created in older versions, it may have had only one cable record (main, or none), because the old logic skipped cable creation for transfer switches. On the first load of the panel, a migration automatically adds the missing main + reserve cables with standard values (cross-section 2.5 mm², length 0 m, method "On the surface"). No data is lost — check the parameters in the ATS properties and update them if needed.
Cable Overview
In Wire Mode → the "Cables" section there is a consolidated list of all the panel's cables: device cables, plus the feeder cables of combs and bars. For each one it shows the state and the current cross-section; if the cross-section is smaller than the calculated one, it also shows the recommended cross-section and an "Apply" button.
The section header carries a summary: a green "All cables are up to date" or a red "N undersized" if any cable has a cross-section below the calculation.
Cable States
| Badge | Meaning |
|---|---|
| ✓ Auto | The cross-section is chosen automatically and always equals the calculated one |
| ⚠ Undersized | The cross-section was set manually and is smaller than the calculated one — needs attention; the recommended cross-section and "Apply" appear next to it |
| ✎ Manual | The cross-section was set manually and is not smaller than the calculated one (including a deliberately larger one) — the system does not overwrite it |
| — Not sized | The cross-section is not calculated because there is nothing to calculate from; the reason is shown on a second line under the cable name |
Reasons for the "Not sized" state:
- the device the cable feeds is not on the board;
- the device is fed directly from the supply — its protective device is outside the board, so the cross-section is not checked;
- there is no breaker or fuse upstream to size the cross-section from;
- the upstream breaker cannot be determined unambiguously;
- the feed of the comb or bar is not assigned;
- the supply source of the bar is not determined;
- sizing for a feed from a bar or comb is not supported yet.
A cable with a manual cross-section larger than the calculated one is not an error: it has the "Manual" state and is not counted among the undersized ones.
Filter and Focus
Above the list is a filter:
- All — all cables
- Auto — cables with automatic sizing
- Undersized — only those that need attention (a manual cross-section smaller than the calculated one)
- Manual — cables with a manual cross-section not smaller than the calculated one
- Not sized — appears only when such cables exist
"Accept Recommendations (N)"
The button at the top of the section is a bulk apply: every undersized cable gets the recommended cross-section and switches to automatic sizing. A confirmation appears first. Everything happens in a single transaction — Ctrl+Z reverts all the changes at once.
"Switch device cables to auto"
The button switches all device cables with a manual cross-section to automatic sizing. Afterwards they show the calculated cross-section — including those that were manually set larger than the calculation. Cables that are not sized stay as they are, and the feeder cables of combs and bars are not changed. If there are manual cables with a calculation among them, a confirmation appears first; the action can be undone (Ctrl+Z).
Inline Editor
Clicking a cable row expands a compact editor right in the list. One cable at a time (accordion): clicking another row collapses the previous one.
While a row is expanded, the corresponding wires are highlighted on the canvas. The Esc key collapses the editor, and the previous wire selection is restored.
Comb Members Are Hidden
Comb members have no individual physical cable — power is fed through the comb teeth from the feeder cable. So the Overview and the bill of materials show only the combs' feeder cables. Individual members appear as a hint in the properties panel.
Automatic Cable Sizing
The recommended cross-section is computed by a pure, deterministic function with no side effects — the result is identical for identical inputs. The sizing takes into account:
- Conductor material: Cu (copper, default) or Al (aluminium)
- Insulation: PVC — the base ampacity tables; XLPE/EPR are modelled
- Installation method: in wall / in conduit / on the surface / underground (app reference table; correspondence to IEC reference installation methods is not confirmed)
- Ambient temperature: correction factor k1 (IEC 60364-5-52 Table B.52.14)
- Cable grouping: factor Cf for cables in a shared bundle/conduit (IEC 60364-5-52 Table B.52.17)
The cross-section is chosen to satisfy all the conditions at once:
- Overcurrent protection: cable ampacity ≥ the rating of the upstream breaker (IEC 60364-4-43 §433)
- Load current: cable ampacity ≥ the load current (IEC 60364-5-52 §523)
- Voltage drop: ≤ 5% (3% for lighting) (IEC 60364-5-52 §525)
- Short-circuit thermal withstand: the conductor withstands the short-circuit current until the protection trips (
I²t ≤ k²×S², IEC 60364-4-43)
The smallest standard cross-section that satisfies all the conditions is the recommendation. The recommendation names the reason the cross-section had to be increased (for example, voltage drop or current), and it is calculated from the nearest protective device that actually limits this cable's current, not simply from the parent device. For three-phase loads with a significant harmonic content, the N conductor is additionally enlarged (up to 1.45× the phase current) per IEC 60364-5-523 Annex E, because 3rd-order harmonics add up in the neutral.
In addition, validation separately checks the cable's thermal withstand on a short circuit, grouping overheating, and behaviour at elevated temperature — see Automatic Checks.