7. Distribution boards, single-line diagram and sizing

Distribution boards

On a three-phase distribution board you can lock the phase of a single-phase circuit-breaker or RCBO. The locked phase is retained at the next automatic allocation; only lock a checked, deliberate manual decision. With complete power data, phase current decides; with incomplete data, circuit count is only an informative estimate. A circuit on a 3- or 4-pole circuit-breaker (or RCBO) is treated as three-phase even if its phase count was left at 1; a three-phase circuit loads all three phases equally, so its missing power does not spoil the phase balance check.

The Distribution boards list, opened from the project page, contains the distribution board enclosures (at most 20 per project). For a new distribution board you give its name, its type (single-phase consumer unit, three-phase consumer unit, meter / service connection enclosure, sub-distribution board), for a sub-distribution board its parent, the enclosure (price list item) and its size (1–6 rows, 6–36 modules per row).

The phase count (1 or 3) can also be set independently of the type; left blank, the type decides (for a consumer unit the type itself is single- or three-phase, for a sub-distribution board / meter enclosure it is inferred from the circuits assigned to it). An explicit phase count takes priority: it decides whether the phase selector appears for single-phase devices, and both the sizing and the rule check use it.

In an NEC (US) project the board type is load center: with a number of spaces, 1- or 2-pole breakers and GFCI/AFCI protection, a printable panel schedule and, on the Boards page, a dwelling load calculation. These are described in the Designing to the NEC chapter.

For a Hungarian-market project, a board can be assigned to a metering point of the Utility connection sheet; the point's calculated demand is computed from that board, and the metering point diagram shows the connection, the small breaker, the kWh meter and the board in sequence (see the Printing chapter, Utility documentation).

The distribution board designer

The designer shows the enclosure as module slots arranged in rows, with fill bars.

The board view resembles a real cabinet: a mounting plate with a DIN rail, a cable duct and an N/PE terminal block, and each kind of device gets its own face. There are two views: Mounting plate is for editing (the terminals and the comb busbar are visible), while Front cover shows the cover plate, which leaves only the device faces free, with blanking covers on the empty positions. The Labels, Phase marking and Comb busbar switches adjust what is displayed, and the browser remembers the setting. The label strip under a device shows its label and the circuit name; on a three-phase board an L1/L2/L3 badge is shown as well. Editing (dragging, arrow keys, Del) works the same way in both views.

On the right, the Add device palette: items are listed as you type a code or text in the search box (the full list is not shown); it only contains price list items that have module data (Module data). If some of your own items have no module data, the palette lists them; for those whose text gives the data, one button adds it, the rest must be entered on the Module data page. If a device has no price list item, the Suggestion button narrows the modules by kind, pole count, width and the circuit's protection; a single match is shown as a preview, with several candidates (or an unknown rated current) you must pick from the list, and nothing is written before you confirm.
Devices can be moved by dragging or with the arrow keys; Del deletes.
Device properties: label, circuits, “Downstream of” (RCD or main switch), phase.
Spare: from the palette you can also place a circuit-breaker, an RCBO or an RCD without a circuit; such a device shows a “Spare” badge in its properties, and you can assign the circuit later in the “Circuits” field.
Smaller / larger rated current: for a device with a price list item, the − and + buttons in the properties step to the next module with a smaller or larger current (kind, pole count, width, tripping characteristic and RCD sensitivity stay the same). The program checks the swap with the usual rules (oversized protection, overloaded circuit). For a circuit-breaker, the Tripping characteristic selector (B, C, D…) switches to the module of the same current with a different characteristic.
Adding a main switch later: if you add a main switch afterwards, the RCDs and circuit-breakers without a parent are automatically placed behind it, so the single-line diagram and the wiring follow at once. When you delete a device, its children move to its parent, and the feed of any sub-board fed from it is cleared; the circuits of the deleted device are marked “not placed” until you give them a new position.
New circuit button; Suggest from circuits: the program offers an arrangement with a preview, which you can accept or discard. If the arrangement does not fit in the enclosure, the program suggests a larger enclosure size that you can set right there. Optimization modes: Standard keeps the established layout, Compact saves space and may offer a smaller enclosure, and Installation makes RCD groups and end-of-row reserve clearer. Modes change positions only; a smaller size needs approval, and module count does not prove physical compatibility. For a board tied to the drawing, the floor's circuits that are not yet tied to a board are included automatically; if the floor has several boards you can choose: only the circuits assigned to this board, all free circuits of the floor on this board, or the free circuits going to the nearest board.
The supply cable and its length can be given (needed for sizing).
Feeding a sub-board: in the sub-board's properties, the Fed from (parent board / device) field selects the parent board and the feeding device (a protective device or main switch). A badge on the feeding device shows which sub-board it feeds, and the Feeds: links in the item panel jump to that sub-board.
Feed in the drawing: in the drawing editor the same selector in the board device's properties offers the parent board and the device. If a drawn cable connects the two boards, the Use the length in the feed button in the cable's properties copies the drawn length into the feed length; such a cable gets no "route without circuit" warning even without a circuit.
Linking to the drawing: on the floor plan, in the properties of the distribution board device, it can be linked to the distribution board, and the list of Connected circuits can be given. The link is visible on both sides (“Linked to drawing” / “Not linked to drawing”).
In a meter enclosure, the meter and the main fuses must be added manually.
EV charger: Suggest from circuits gives every charger circuit its own RCD, preferably type B or EV (type A only if built-in DC fault current detection, RDC-DD, is ticked for the charger); the inverter and heat pump circuits get a note. Details: the Solar, EV charging and heat pumps in the design chapter.
The program suggests the incoming-supply order that matches the market of the project owner. In Greece it is main switch → main fuse (fuse disconnector) → RCD; in other markets the usual main switch → RCD. This is practice and a suggestion, not a standard clause. If the drawing deviates, the Incoming order rule (BETAP_SORREND) warns; it can be adjusted or switched off on the Rules page. The feature sits behind a service switch.

In the palette, the Quantity selector (1–24) lets you place several identical devices at once: the button puts that many copies side by side in the first free spots, with a single save. If they do not all fit, those that fit are placed and a notice appears. Afterwards, Name them… (or Name devices of this type on one device) lets you name them line by line in one window or fill them with a prefix and a start number (e.g. F1…F6).

Accessory devices

Busbars: Neutral busbar, PE busbar.
Indicators and meters: Phase indicator lamp, Sub-meter (kWh), Phase/voltage monitoring relay.
Control: Staircase timer, Impulse relay, Time switch, Bell transformer, DIN rail power supply.
Protection and other: Fuse disconnector, Load isolator, DIN rail socket outlet, Motor protection switch.

If you give a device a catalog code, it is included in the takeoff.

Terminal strip

With “terminal strip” wiring, the mounting plate shows an automatic terminal strip (X1) built from the terminal list: it goes to the right end of the first free row and can be dragged elsewhere with the mouse. If it does not fit, a separate rail appears at the bottom and a warning is shown. The takeoff includes the terminals, end plates, blanking covers and comb busbars.

You can delete the X1 strip with the Delete terminal strip X1 button above the mounting plate (after confirmation): the board switches to “direct” wiring and the terminals stay on the devices. The Restore terminal strip X1 button in the same place brings it back.

The default wiring mode is Main-circuit branch terminal (the Terminal strip value gives the X1 strip): it puts a single shared block on the mounting plate instead of the X1 strip: L, N, PE poles on a single-phase board, L1, L2, L3, N, PE on a three-phase one (the phase count comes from the board or its circuits). The conductors of the circuits connect to the matching pole of the block (X1:L1, X1:N, X1:PE in the list), the block can be dragged like the strip, and the takeoff gets one branch terminal (no per-terminal DIN terminals or end plates).

Checking the distribution board

The designer's Rule check panel runs rules: standard rules (e.g. missing RCD, missing or oversized protection, overloaded circuit), physical rules (does not fit in the enclosure, no module data, not placed), structural rules (difference from the drawing link) and practical rules (RCD loading, lighting behind one RCD, phase balance, spare ways, main switch). You can switch the practical rules on/off on the Distribution board rules page, and you can also set their severity and threshold; the standard and physical rules are fixed. Info findings can be hidden.

RCD requirement. Whether a circuit needs a 30 mA RCD is decided from both the circuit name and the drawing: if you drew a socket outlet or a luminaire on the circuit, or one of its devices is in the bathroom, the circuit requires an RCD even if its name suggests otherwise. The program also looks for the RCD along the supply chain: the circuits of a sub-board can be protected by an RCD in the parent board. With TT earthing (the project's Earthing system data) every final circuit without an RCD gets an error, because there fault protection needs an RCD; the fault loop (Zs) is then not calculated. In a TN system a circuit behind an RCD on which the circuit breaker may not disconnect (Disconnection not assured) only gets a warning. The RCD too small rule reports when the rated current of the RCD is lower than the estimated simultaneous current of the circuits and sub-boards behind it; the automatic layout does not silently pick an RCD or main switch that is too small either. Next to a "no module data" error there is a Pick from catalog button (also in the suggestion preview): the program reads the catalog item texts (type, poles, trip curve, current, mA), records the missing module data, and sets the matching item on devices that have none yet. It writes to your own settings, never overwrites existing module data, and tells you if no suitable item is found. If several catalog items fit, the program asks which one to use and remembers your choice.

Single-line diagram

An overview of the distribution board designer is given on the Distribution board designer page. For single-line diagrams in general, with an example figure: Single-line diagram. The Single-line diagram button opens the single-line diagram calculated from the distribution board and the circuit list (it is not a stored drawing; it always shows the current data). The paper size (A4/A3) and the orientation can be chosen; with many outgoing circuits it breaks onto several sheets, with a standard title block; Print / Save as PDF. The sizing columns (Ib, ΔU) also appear on it. If there is an error in the distribution board data, or a circuit does not get onto the diagram, a warning tells you.

Multi-line current-path diagram and terminal schedule. With the view switcher on the single-line page you can switch to the multi-line diagram of the current paths: every conductor is shown from the busbars through the device poles and terminals to the cable and the load. In the board settings the wiring method is Main-circuit branch terminal (the default: one shared block with L, N, PE or L1, L2, L3, N, PE poles), Terminal strip (the cables land on the terminals of the terminal strip) or Directly on the device (the conductors go to the device terminals, without a strip). The Terminal schedule page (opened from the board page) lists the terminals per conductor with a drawing of the terminal strip, the current path per circuit (supply, device, terminal, cable, load), and finally the material requirement (terminals, end plate, rail module); the calculated data are informative. The two diagrams and the schedule can also be switched on as sheets in the plan package (per board), where they are part of the page numbering and the table of contents.

Sizing (informative calculation)

In the designer's Sizing panel you see, for each circuit: the power (given, or suggested from the devices), the design current (Ib), the rated current of the protection (In), the current-carrying capacity of the cable (Iz), the length and the voltage drop including the drop of the supply; a value over the limit is red. For each distribution board it totals the phase loads and the size of the main switch. You can take the suggested power over into the circuit with one click (as an editor).

Grouping and temperature: if several power circuits run together along a cable route (e.g. in one conduit), the current-carrying capacity is reduced by the grouping factor (×0.70 for 3 circuits); you can set the ambient temperature on the Distribution board rules page (default 30 °C). The correction is shown as a small number below Iz.
Disconnection (Zs): the program calculates the fault loop impedance (supply Ze + supply cable + the circuit's line and protective conductors), and checks that the circuit-breaker reliably trips (B: 5×, C: 10×, D: 20× In). If not, Zs is red, and the largest permitted length is shown. Set the value of Ze (default 0.35 Ω) according to an on-site measurement or the supplier's data.
Length: if a distribution board belongs to the circuit on the drawing, the length is the longest path from the distribution board to the farthest device (for a branching circuit, not the sum of the branches). Without a distribution board, or with a disconnected drawing, it is the sum of the cable routes; a note indicates this.

Inputs: for the circuit, the power, cos φ, the diversity factor and the length; for the distribution board, the supply cable and its length.

Sub-board feed in the sizing. If a board is fed from a device of another board, the program checks the feed with two rules (Ib ≤ In ≤ Iz): the simultaneous current of the sub-board (together with its own sub-boards) must not exceed the rated current of the feeding protection (Sub-board feed overloaded), and the rated current of the protection must not exceed the current-carrying capacity of the feed cable (Feed cable not protected); the latter is calculated with the less favourable installation method B2. It reports an error if the feed does not comply. If the feeding device is an RCD or a main switch, the program measures the feed against the nearest overcurrent protection along the supply chain (in the parent board, or failing that the upstream protection of the supply); if there is none, it warns that the feed cable is not protected against overcurrent. For a gG-fused feed the condition is stricter (I2 ≤ 1.45 · Iz): from 16 A the rated current of the fuse may be at most 0.906 times the current-carrying capacity of the cable.

Quick calculators. If you need the sizing for a single circuit rather than from the drawing, you can try the same formulas in the Electrician calculators strip on the home page (even without signing up): voltage drop, cable cross-section and circuit-breaker, power and current, as well as Ohm's law, energy cost, power factor correction and material estimate. The calculators are informative single-circuit versions, and the form values can be shared in a link.

Basis of calculation. The Calculation basis button in the sizing panel row opens a window for that circuit: where each input came from (given, default, from the circuit role, from the drawing or assumed), what conditions (e.g. copper conductor, PVC insulation, ambient temperature, grouping) and what sources the program used, and what limits the result (missing data). A summary badge in the header shows how many of the value groups used are verified. "To be verified" means the value has not yet had a professional review; it is not an error but information, and it does not mean the value has been checked against a standard. Responsibility does not change: the window only makes the calculation transparent, and the designer remains responsible for the correctness of the sizing and for compliance with the standards.

Informative calculation. The current-carrying capacity tables, the voltage drop formula and the limit values are awaiting approval by an electrical designer. The calculation does not replace the designer's responsible sizing.

Short-circuit current and selectivity

In the Supply dialog (project page, "More settings") you can enter the fault data: the prospective short-circuit current at the connection point (Ik3), or your own transformer (Sn, uk), or the type and rating of the upstream protection; the source priority is Ik3 > transformer > Ze. From these the program calculates, as an informative estimate, the largest short-circuit current at the board busbar (shown in the Sizing panel header) and the smallest one (the Ik min column per circuit).

Breaking capacity: the rated breaking capacity (Icn) of a miniature circuit breaker must not be lower than the largest short-circuit current at the busbar; a device without Icn data cannot be judged.
Supplying protection: for a sub-board the smallest short-circuit current must be large enough for the instantaneous trip of the supplying breaker.
Selectivity: the Selectivity panel gives a verdict for each upstream–downstream pair (selective, partial, not selective, cannot be judged); clicking a row shows the trip bands. Below 0.1 s only the manufacturer's selectivity table decides; for a gG fuse upstream the verdict is currently "cannot be judged". The rule can be switched on the Board rules page; the fault calculation sheet in the "Calculation appendix" group of the plan package prints the same.

Informative calculation. The factors (c_max/c_min, x', ρ) and the points of EN 60898-1 are awaiting verification. The feature is not valid in NEC (USA) projects.

Module data from the catalog

On the Module data page, the Add missing module data from the catalog button lists in a preview the price-list items that can be interpreted and have no module data yet. After checking, Save records them; existing own or shared data is not overwritten. For an ambiguous item you choose from a list; in shared mode only an admin can do this.

Printing labels

In the board view, the Labels button opens label printing in a new tab. There are two modes: Device strip (the device labels of the board in one row) and Label sheet (standard A4 label layouts or a custom size; set the Start cell to continue a partly used sheet). When printing, set the scale to 100 % (not "Fit to page") and no margins, otherwise the labels shift.