Protection Hierarchy

The protection hierarchy is the set of "parent → child" relationships between the devices in your panel. It defines which device protects which circuit, and it is the basis for automatic selectivity validation.

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Concept#

In a real panel, devices are wired in series: power enters at the incomer, passes through an isolator or an incoming MCB, then through an RCD, and on to the group breakers that feed the final circuits.

ElectroBoard models this structure through the "Parent device" field on every device. When you set a parent, the conductors between them are drawn on the schematic automatically.

Typical single-phase hierarchy:

Isolator (63 A)
└── RCD (40 A, 30 mA)
    ├── MCB "Lighting" (10 A, curve B)
    ├── MCB "Room sockets" (16 A, curve C)
    ├── MCB "Kitchen sockets" (16 A, curve C)
    ├── MCB "Water heater" (16 A, curve C)
    └── MCB "Laundry" (16 A, curve C)

Typical three-phase hierarchy:

Incoming MCB (40 A, 3P)
├── RCD L1 (40 A) — phase L1
│   ├── MCB "Lighting, floor 1" (10 A)
│   ├── MCB "Living-room sockets" (16 A)
│   └── MCB "Water heater" (16 A)
├── RCD L2 (40 A) — phase L2
│   ├── MCB "Lighting, floor 2" (10 A)
│   ├── MCB "Kitchen sockets" (16 A)
│   └── MCB "Laundry" (16 A)
└── RCD L3 (40 A) — phase L3
    ├── MCB "Bedroom sockets" (16 A)
    ├── MCB "Oven" (20 A)
    └── MCB "Outdoor lighting" (10 A)

Setting the Parent Device#

1. Select the device you want to assign a parent to
2. In the properties panel, find the "Parent device" field
3. Pick from the list — it shows every device that can supply power downstream

The conductors from parent to child appear on the schematic immediately.

⚠️ Note: When you change the parent device, the breaker is automatically removed from the busbar comb it belonged to. This is required because a comb needs a shared parent for all of its members. A toast notification about the removal is shown.

Who Can Be a Parent or a Child#

Not every device can have children or a parent:

Device	Can be a parent	Can be a child
MCB	✓	✓
RCD	✓	✓
RCBO	✗	✓
Isolator	✓	✓
Contactor	✓	✓
ATS	✓	✓
Changeover 1-0-2	✓	✓
Phase selector (FK)	✓	✓
Contactor control switch	✗	✓

For example, an isolator often sits at the incomer (a parent with no parent of its own), but it can also be an intermediate disconnector in a sub-panel. An MCB usually terminates a circuit, yet it too can feed another device below it (e.g. a sub-panel MCB).

💡 Technical exception: RCBO, AFDD and fuse are marked "not a parent" in the table — that is their typical role as an end-of-line device, so they do not expect children (and are not flagged with a "no connected devices" warning). Physically, however, they have a load-side output terminal and can feed a device below — so they are available in the parent-picker list. An SPD (a varistor shunt) and a socket/meter, by contrast, have no load output and can never be a parent.

Phase selector — cascade update#

The phase selector (FK) has a unique behaviour: it accepts a three-phase input (L1+L2+L3) but outputs only one selected phase. When the "Output phase" parameter (L1/L2/L3) changes, all single-phase child devices automatically move to the new phase. Children cannot choose a phase on their own — it is fixed by the parent phase selector.

Phase propagation#

The same cascade logic applies to busbar combs and 1P/1P+N child devices under a three-phase parent. When the phase of a 1P/1P+N parent changes, the system automatically updates:

• the corresponding single-phase comb
• all single-phase children of that comb
• single-phase children further down the subtree

Conditions: three-phase parents (3P/3P+N) do not propagate — each child picks its phase independently; 2P descendants are left untouched.

ATS and the 1-0-2 Changeover — Dual Connection#

An ATS (Automatic Transfer Switch) and a 1-0-2 changeover switch both have two power sources: main and reserve. So they have two parent devices:

• Parent device — the main source (e.g. the incoming MCB from the grid)
• Additional source (2nd) — the reserve source (e.g. an MCB from a generator or a second supply)

Both fields are set in the properties panel under "Hierarchy". A conductor from each source appears on the schematic automatically.

Typical scheme:

Incoming MCB (grid) ──────┐
                           ATS / QC (63 A) ──── load
Incoming MCB (generator) ──┘

Difference between an ATS and a 1-0-2 changeover:

• ATS — automatic transfer when the voltage disappears. The switching time is set in the parameters (5 s by default). It also supports a manual mode (1-0-2)
• 1-0-2 changeover — manual transfer only. Three positions: source 1 / off / source 2. No automatic voltage monitoring

💡 Input cables: each input of an ATS/changeover has its own cable field — main (from the grid) and reserve (from a generator/UPS). Both fields are available in the "Input cables" section of the properties panel and are included in the BOM. Validation checks each cable independently per IEC 60947-6-1.

Power Source Roles#

For incoming devices (a root with no parent, or the secondary parent of an ATS/changeover) the source role is set right inside the "Source" section of the properties panel — the type, name and options are gathered in one place. This lets you classify inputs for easy navigation of a panel with reserves.

Supported roles:

• 🔌 Grid (grid) — centralized utility supply
• 🔀 Transformer (transformer) — substation with its own earthing system
• ⚡ Generator (generator) — diesel/petrol
• 🔋 Inverter (inverter) — hybrid or off-grid
• 🛡 UPS (ups) — UPS with a battery
• ☀️ Solar (solar) — a solar panel straight into the panel
• 🔋 Battery (battery) — a standalone battery installation
• ⚙️ Other (other) — with a custom name

Automatic assignment for an ATS/changeover: when you set the two inputs, the system automatically assigns the "Grid" role to the main input and "Generator" to the reserve. This happens only if neither input already has a role assigned — your manual choice is never overwritten.

Where the roles are shown:

• The "Source" section — for an incoming device the role is picked right here (a role-coloured preview chip). For an ATS/changeover the "Main" and "Reserve" inputs have separate role badges that can be edited in place (✎).
• "Power" on downstream devices — any device below a transfer switch shows the full set of possible sources it can be fed from (e.g. "Grid / Inverter"), labelled "via ‹switch›". With three or more sources it collapses into an "N sources" disclosure. This answers "where is this device powered from" at any depth of the hierarchy.
• Canvas — a coloured square in the top-left corner of incoming devices (a screen reader reads the name from the label).
• BOM/PDF — a dedicated "Source" column with the role icon and name.
• AI consultant — the roles are included in the context — you can ask about the reserve system in natural language.

⚠️ Validation: if an incoming device with children has no assigned role — a hint is shown. If an ATS has two inputs with the same role (e.g. both "Grid") — a warning that the reserve makes no sense. If a device with the role inverter/generator/solar/battery/UPS is not itself a protective device and has no MCB/RCBO/fuse upstream — a "source without a protective device" error.

2P Mode (L+N)#

For the 2P connection variant on an MCB/RCBO/fuse/contactor/time relay/isolator, an explicit "2P mode" choice is available in the properties panel:

• L + N — protection of both poles of a single-phase supply (typical for the residential sector). Children receive a single-phase L+N output.
• L1 + L2 — two phases without a neutral (a split-phase inverter/generator branch). The neutral is not available through this device; child devices that need N take it from the panel's common N bar.

💡 The default is chosen automatically: if an ancestor in the supply chain is a source with the role inverter / generator / solar / battery without a neutral — a new 2P child gets L1+L2; otherwise L+N.

Exceptions:

• A 1-0-2 changeover in 2P mode — always L+N: in a domestic scheme the switch output is ALWAYS L+N regardless of the inverter type on the reserve input. The L2→N bonding for an isolated inverter happens physically at the panel incomer.
• 3P/3P+N/4P — a fixed pole set (L1+L2+L3 or L1+L2+L3+N); no mode choice is needed.

Mode indicator in the SVG: the phase badges inside the device body match its actual poles (L+N → one L badge; L1+L2 → two [L1][L2] badges). There is no separate "mode" badge — the mode is visible from the poles.

Contactor Control Circuit#

Contactors are driven through a control circuit — separate from the power circuit. In ElectroBoard this is modelled through a "controller → contactor" link:

• Controllers — contactor control switch, time relay, voltage relay, multi-function relay, smart controller
• Target — the contactor (a device with an A1/A2 coil)

The controller's properties panel has a "Control" section where you pick the contactor. After the choice:

• An L wire is generated from the controller to coil terminal A1 (top of the contactor)
• An N wire is generated from terminal A2 (bottom of the contactor) to the N bar
• The control-circuit wires are drawn as a dashed line with a thinner stroke

Several controllers can drive one contactor (e.g. a switch + a time relay). Only one coil N wire is generated.

Neutral (N) Routing#

ElectroBoard uses a declarative model for routing the neutral — it defines where each device takes N from and where it distributes it:

• N source — where the device takes the neutral from: from supply (root), from parent, via bar, or unassigned (the system resolves it automatically).
• N output — where the device distributes the neutral to its children: direct (from its own N output) or via bar (through its own N bar).
• Bar owner — which device "owns" an N bar (RCD, ATS, distribution block).
• Protection zone — the chain from an RCD to the final device; the system tracks it so the neutral is not mixed between zones.

The panel format is versioned, and when an older file is opened all N routes are migrated automatically. The full N-route graph is built in a single pass over the hierarchy — the basis for all N checks.

N Bars Under an RCD (Automatic Lifecycle)#

When you connect an MCB under an RCD, the neutral (N) conductor must pass through a separate N bar that belongs to that RCD. ElectroBoard automatically creates and deletes such bars based on actual usage.

Automatic lifecycle rules:

• Lazy creation: a new RCD (RCBO/ATS/changeover 2P L+N) with no children does not get a bar immediately. The bar appears when the first child moves to via bar mode.
• Sibling-aware default: when you add a new N child under an RCD, the system picks the route itself:
  • 0 existing N siblings → direct — a single wire from the RCD's N output, no bar needed
  • ≥1 N sibling → via bar — the bar is created automatically so a single N terminal is not shared
• Auto-delete: when all children of the RCD move to direct or are removed — the bar is deleted automatically, and remaining children are set to explicit direct.
• Migration: when older panels are loaded, orphan auto-created bars with no consumers are cleaned up.
• Validation threshold: 1 direct under an RCD → OK, 2 direct → warning (physically possible, but a bar is better), 3+ direct → error (physically impossible on a single N terminal).

Devices that create their own N bar (when needed):

• RCD 2P/4P — to isolate the neutrals of protection groups
• RCBO — the same logic (if it has children with N)
• ATS 4P and changeover 1-0-2 2P L+N / 4P — to switch the neutral per IEC 60947-3 (a TN-C-S system). Bar label: "N (ATS)" / "N (Changeover)"

Voltage relays, meters and contactors (without their own bar) connect to the panel's common N bar.

This matters because in a real panel mixing the neutrals of different RCD groups causes nuisance tripping.

💡 N-bar lifecycle: the N bar of an RCD/RCBO/ATS/changeover exists only while at least one child is in "via bar" mode. When all children move to "direct" — the bar is removed automatically. This prevents "orphan" bars from accumulating as you edit the panel.

⚠️ L1+L2 mode context: when an ancestor is in 2P L1+L2 mode (not L+N), it has no N pole. Child devices with N get a warning if there is no common N bar on the panel to carry the neutral through. Add an N bar or change the ancestor's mode to L+N.

The properties panel, under "Hierarchy", shows:

• Source — the parent device + the reserve source (for an ATS/changeover)
• N route — an interactive N-source picker with a hint of the full protection chain
• Group N bar — the separate N bar that belongs to this device (for an RCD)
• Bars — PE and N connections (compact chips)
• Connected devices — a list of child MCBs with their ratings

The "N Bar" Section — Interface#

The "N bar" section in the RCD/RCBO/ATS/changeover panel has a rethought interface:

• N-source picker — instead of a plain "bar / direct" toggle, it shows an N-source choice with the protection-zone context
• Protection chain — a linear hint that shows the full protection chain from the incomer to the current device
• AutoFix hints — when an N-route problem is detected, a "Merge N? Yes / No" prompt is offered that automatically creates a bar and reassigns the connections
• ATS wizard — when configuring an ATS with two sources: step 1 — pick the sources, step 2 — configure the N logic

N Route#

For devices with an N pole, a choice of N-conductor route is available:

• Via bar — N goes through an N bar (common or group). Recommended for most scenarios
• Direct from parent — N comes straight from the parent device. Suitable when the parent passes N through (e.g. a voltage relay → an ATS)

The system determines the optimal route automatically. On a problem (N is broken, N bypasses protection) — a warning appears with a button to jump to the cause.

Selectivity#

Selectivity is the principle that, in a fault, only the protective device nearest to the fault location trips — not everything upstream. ElectroBoard checks selectivity automatically:

• A child's rating must not exceed the parent's rating — otherwise, on overload, the parent trips and disconnects the whole group instead of a single circuit. An equal parent/child rating is also unsafe (it is unclear which one trips first).
• The parent's curve must not be faster than the child's curve — e.g. a parent with curve B and a child with curve D: the parent trips first on a short circuit and disconnects the whole group. The parent's curve must be the same or slower.
• The sum of child ratings must not exceed parent rating ÷ RDF — where RDF (the rated diversity factor per IEC 61439-1) depends on the number of outgoing circuits: from 1.0 for a single circuit down to 0.5 for 10+. For example, 5 children under a 40 A device → threshold ≈ 57 A (40 ÷ 0.7). This is not a fixed margin but a realistic simultaneous-current calculation.
• RCD differential selectivity — the parent RCD's IΔn must be at least three times the child's IΔn (e.g. parent 100 mA, child 30 mA), per IEC 61008-1; otherwise both trip on a leakage.

💡 The checks apply to protective devices: ratings and curves are compared only for MCBs, RCBOs, AFDDs and fuses. RCDs, contactors and relays are excluded because they do not perform overload protection.

See also: Automatic Checks