What a good board design has to deliver
A distribution board is the point where a single supply becomes many circuits. Designing one well means deciding, before anything is ordered or built, how many ways are needed, which devices go in them, how the outgoing circuits are grouped, and how the load is spread across the supply phases.
A design that is thrown together on site tends to show its faults later: a board with no spare ways, phases loaded unevenly, or RCD groups that trip half the installation when one circuit faults. A short amount of structured design work removes all of those problems while the layout is still on screen.
This guide follows a repeatable order: gather the connected loads, count the modules, group the circuits, balance the phases, lay out and label the board, and finish with a final check. The same sequence works for a domestic consumer unit and for a large multi-way distribution board.
Step 1: gather the connected loads
Every decision later in the process depends on knowing what the board will feed. Start by listing each outgoing circuit with its purpose, its expected load and the cable size you intend to run.
- Circuit name and what it supplies.
- Design current, taking diversity into account where the standard allows it.
- Cable size and installation method.
- Whether the circuit needs earth-leakage protection and at what sensitivity.
- Whether it is single-phase or three-phase.
This list is the backbone of the whole design. In GorkyCAD Pro it becomes the circuit data held in the model, so the same information feeds the calculations, the schematic and the cable schedule without being re-entered by hand.
Step 2: count the modules
Distribution board capacity is measured in modules, each a fixed width defined by the enclosure standard. Add up the module width of every device you plan to fit, then allow room for spares. The table below gives typical widths to guide the count; always confirm against the manufacturer's data for the exact devices specified.
| Device | Typical width (modules) | Notes |
|---|---|---|
| Main switch or main breaker | 2–4 | Depends on poles and rating |
| Single-pole MCB | 1 | One way per circuit |
| Double-pole RCBO | 2 | Overcurrent plus earth leakage |
| RCD | 2–4 | Shared by a group of circuits |
| Surge protection device | 2–4 | If the project requires it |
Total the widths, then add a sensible margin for future circuits. A board filled to the last module leaves no room for growth, and the next electrician to visit has to add a second enclosure. Choosing an enclosure one size larger than the bare minimum is usually cheaper than a rebuild later.
Step 3: group circuits and choose devices
Grouping circuits is about how they behave together, not just how many there are. Circuits sharing an RCD should be chosen so that a single fault does not plunge the whole installation into darkness.
Separate critical and non-critical loads
Keep lighting and other essential circuits away from groups that are likely to trip. If a fault in a socket circuit can black out the stairs, the grouping is wrong.
Match the device to the circuit
Each way gets a protective device sized for its cable and its load, chosen with the correct tripping characteristics for the equipment it feeds. Get this wrong and a perfectly good cable ends up either unprotected or tripping on normal inrush.
Keep spares identifiable
Leave spare ways clearly marked rather than as anonymous gaps. A spare that is visibly a spare is an invitation to extend; a blank space is a puzzle.
Step 4: balance the phases
On a three-phase board, single-phase circuits are assigned across the phases. A board where one phase carries most of the single-phase load is out of balance: that phase runs hotter, voltage drop is uneven, and the neutral carries current it need not carry.
- List every single-phase circuit with its design current.
- Sort them by load, largest first.
- Assign each in turn to the phase with the lowest running total.
- Check the final totals across phases and adjust the largest movers if the spread is still wide.
- Keep the assignment on the drawing so the next person can see why it was done that way.
Perfect balance is rarely possible, but a deliberate attempt to spread the load is far better than assigning circuits in the order they were listed. Three-phase loads such as motors are inherently balanced and simply occupy their own ways.
Step 5: lay out and label the board
The physical layout should follow the logic of the design. Group the devices the way the circuits are grouped, keep high-power devices within their thermal limits, and leave room for cable entry and bending radius.
Then label everything, because a board without labels is a board nobody can maintain. Give each way the name used in the schedule, mark the main device with its source and rating, and show which ways each RCD covers. Keep a written schedule that matches the physical labels exactly, and update it whenever a circuit changes.
In GorkyCAD Pro the layout, the panel schedule and the labels are generated from the same project model. Because the naming is defined once, the drawing, the schedule and the printed labels agree by construction rather than by careful proofreading.
Step 6: the final check before sign-off
Before the design leaves your hands, run it once more against the requirements:
- Every planned circuit has a way, and every way has a device sized for its cable.
- Earth-leakage coverage protects the circuits that need it without grouping unrelated loads.
- Phase loading is reasonably even across the supply.
- There are spare ways, and they are marked as spares.
- The layout leaves room for cable entry and future additions.
- Labels and the written schedule match, and both match the drawing.
GorkyCAD Pro carries 70+ calculations and IEC 60364 checks in the same model as the board design, so cable sizing, voltage drop and protective device coordination are verified while the layout is being arranged. The result is a design that can be ordered, built and documented from a single source.
From design to built board
A distribution board designed in this order is easier to build, easier to inspect and far easier to extend. The module count comes from real data, the grouping reflects how the installation will actually behave, and the phases are balanced on purpose. None of it takes long when the design lives in a tool that holds the circuits, the calculations and the documents together.
Start from the connected loads, work outwards to the enclosure and the labels, and finish with the check. That sequence turns a pile of components into a board someone can trust for years.
FAQ
How many spare ways should a board have?
There is no single number, but leaving a margin rather than filling the enclosure to the last module avoids adding a second board at the first change.
Why balance the phases on a three-phase board?
Even loading keeps each phase cooler, reduces uneven voltage drop and limits current in the neutral compared with a badly unbalanced board.
Should lighting share an RCD with socket circuits?
Usually not. Keeping lighting separate from circuits that are more likely to trip means a fault does not leave the installation without light.
Where does the device rating come from?
From the cable it protects and the load it feeds. The protective device must be coordinated with both, which is why the circuit list is built before the layout.