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 number of cables in the bundle — ampacity correction factors (k1 and Cf)
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 IEC 60364-5-52 range (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. Classification per IEC 60364-5-52:
| Method | Ref | Description | Ampacity (2.5 mm² Cu/PVC) |
|---|---|---|---|
| In a wall (chase) | A2 | Cable in a chase under plaster | 21 A |
| In conduit / duct | B2 | Cable in a corrugated conduit or duct | 24 A |
| On the surface | C | Cable clipped directly on the surface | 27 A |
| Underground | D1 | 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
The installation method for new devices is set globally in "Panel settings" (the gear icon → "Default cable installation" section). The base default is On the surface: it matches the real panel scenario (conductors leave the enclosure in free air, and only on the way to the load do they enter a wall or conduit).
Changing this setting affects new devices only — existing cables keep the method chosen earlier. For a project with concealed wiring you can set "In a wall" for the whole panel.
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) is correct, because the breaker trips before the cable overheats. A 1.5 mm² cable in a wall chase (15.5 A) under the same 16 A breaker is insufficient: the rating exceeds the permissible current, so on an overload the cable reaches 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. For each one it shows the state, the current cross-section, the recommended cross-section (if different), and an "Apply" button.
Cable States
| Badge | Meaning |
|---|---|
| ✓ Auto | An auto-generated cable with the current cross-section per the standard |
| ⚠ Auto (stale) | Auto-generated, but the recommendation has changed (a standard change or updated ampacity tables) |
| ✎ Manual | The user set the cross-section manually — the system does not overwrite it |
Filter and Focus
Above the list are three radio buttons:
- All — all cables
- Stale — only those that need attention (stale auto-recommendations)
- Manual — cables with a manual cross-section (protected from auto-fix)
"Accept Recommendations (N)"
The button at the top of the section is a bulk apply: it rewrites stale auto-cables to the recommended cross-section. If the scope includes manually configured cables, a confirmation appears: "Of N cables, M are manually configured. Accepting the recommendations will switch them to auto. The action can be undone with Undo." Everything happens in a single transaction — Ctrl+Z reverts all the changes at once.
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 per IEC 60364-5-52
- Installation method: A2 / B2 / C / D1 (IEC 60364-5-52)
- 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 three 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)
The smallest standard cross-section that satisfies all three conditions is the recommendation. 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.
Separately, validation checks the cable's thermal withstand on a short circuit (I²t ≤ k²×S², IEC 60364-4-43), grouping overheating, and behaviour at elevated temperature — see Automatic Checks.