Free design exercises
A circuit designer that uses the application’s real engine, a recipe of the minimum circuits of a dwelling and design exercises driven by the client’s request, validated against I7 in real time. The full dwelling design (plan, rooms, distribution board) is done in the ElectroSchema editor.
Circuit designer
Power → recommended Ib + cross-section + MCB (the app engine); then you choose and get a verdict
K1 — reference 30 °C (Annex 5.18)
K2 — 1 = a single circuit (Annex 5.19)
A = thermally insulated wall · B = conduit on wall (B2 reference) · C = on wall · D = buried · E/F/G = free air
Engine recommendation (calc-engine)
Design current Ib
9.2 A
Recommended cross-section
1.5 mm²
MCB
10 A · C
Total K factor (K1 × K2 × method D × K3)
1
Calculated with the real engine of the app (calc-engine): Ib from the power, then the MCB from the app’s series of ratings and the smallest cross-section whose corrected Iz covers both the rating and the 1.25 reserve — the same pure functions the Vitest tests use. Iz is read from Annex 5.10 (A1, A2, B1, B2, C) or from Annexes 5.11/5.12 (E, F, G), in the column of the installation method and of the number of loaded conductors: 2 for single-phase, 3 for three-phase. For F and G the annexes only give values from 25 mm² upwards, and G has columns only for three cables. The K factor shown is K1 (temperature) × K2 (grouping) × K3 (soil, only for buried laying) × the method factor, which applies only to D: buried laying starts from column B2 with an estimated factor, because Annex 5.22 is not integrated. The engine does not propose a cross-section whose corrected Iz is exactly equal to the breaker’s In: the code allows it, and if you choose it yourself (In = corrected Iz) the verdict stays “Compliant”, but any deviation in temperature or grouping makes it non-compliant — which is why the recommendation goes up one size. Equality with the 1.25 reserve is accepted: the strict margin applies only to In.
The verdict applies only the normative condition Ic ≤ IN ≤ Iadm (Art. 4.3.2.1.3), with Iadm = Iz × K; the 25 % reserve is the app’s recommendation and is flagged separately.
Board recipe — the minimum circuits
The circuit list of a dwelling; tick what you included in the project
A dwelling board starts from a minimum set of circuits: dedicated ones for large loads, common sockets limited to 2 kW, separate lighting, a bathroom with RCD, plus the general protections. Tick each circuit as you add it.
Still 10 circuits to add for a complete recipe.
Calculation assumptions and scope
- The app’s real engine: the calculations come from `calc-engine` (calcCurrent, recommendCircuit, cableIz) — the same pure functions the Vitest tests use. The editor’s automatic sizing runs on a separate module (protectionDesigner, default cos φ 0.85), so it can give different values from this page (cos φ 0.95).
- The normative condition is Ic ≤ IN ≤ Iadm, with Iadm accounting for the correction factors (Art. 4.3.2.1.3); on top of it the app adds a 1.25 design reserve on the working current, and the cross-section and the MCB are chosen together, so that In never exceeds the corrected Iz
- The normative limits used: common sockets ≤ 2 kW (Art. 5.4.7), dedicated circuits for loads > 2 kW, RCD ≤ 30 mA in bathrooms (Art. 7.1.3.5), SPD in the main board (Art. 4.4.2/4.4.3)
- The page is educational (a single circuit + the board recipe); the complete design of a dwelling is done in the ElectroSchema editor, with I7 validation on the final result
Go deeper on the blog
Designing an installation — step by step
From the load list to circuit sizing, dedicated circuits, protections and balancing.
A. The design method — from loads to circuits
Inventory the loads
List all the loads room by room: lighting, sockets, fixed appliances (hob, oven, water heater, washing machine), air conditioning. For each: the power and whether it is single- or three-phase.
Group them into circuits
Large loads (> 2 kW) get a dedicated circuit; the rest are grouped on common circuits (sockets ≤ 2 kW, separate lighting). Each circuit will have its own protection.
Size and protect each circuit
For each circuit: you calculate Ib, choose the cross-section (with the 1.25 margin and the K factors), then the MCB (Ib ≤ In ≤ Iz) and the RCD where required.
B. Sizing a circuit
Design current Ib
Ib = P / (U × cos φ) · three-phase: Ib = P / (√3 × 400 × cos φ)
E.g.: water heater 3000 W single-phase, cos φ = 0.95 → Ib = 3000 / (230 × 0.95) = 13.7 A.
The cross-section with the design reserve and the K factors
Iz_table × K1 × K2 ≥ Ib (code) · the app adds a 25 % reserve: ≥ Ib × 1.25
Design current = Ib × 1.25 = 17.2 A. In single-phase (2 loaded conductors) 1.5 mm² has only 16.5 A, so the first cross-section with Iz ≥ 17.2 A (at K = 1) is 2.5 mm² (Iz 23 A).
The MCB
In = the first standard rating ≥ Ib (6, 10, 13, 16, 20, 25…). For 13.7 A → 16 A. You check In ≤ Iz: 16 ≤ 23 ✓.
Art. 4.3.2.1.3 — I7-2011
“Ic ≤ IN ≤ Iadm” — the design current ≤ the rated current of the protective device ≤ the current-carrying capacity of the conductor.
C. Dedicated vs common circuits
The 2 kW rule
A common socket circuit does not exceed 2 kW installed power. Above this value (washing machine, air conditioning, hob) → dedicated circuit.
Why dedicated
A large load on its own circuit does not “steal” from the others, has a protection sized exactly for it and can be isolated for maintenance without shutting down the rest.
Art. 5.4.7 — I7-2011
“The power installed on a single-phase socket circuit in residential and social-cultural buildings is 2kW. In dwellings, for loads with powers above 2 kW (e.g. washing machines, air-conditioning units, etc.), separate socket circuits must be provided.”
D. The mandatory protections
RCD ≤ 30 mA and SPD
General-use socket outlets and current-using equipment with In ≤ 32 A (Art. 4.1.5.2.1, amended by the 2023 updates) and all bathroom circuits (Art. 7.1.3.5) are protected by an RCD ≤ 30 mA; the main board gets the first stage of overvoltage protection, usually a type 2 SPD (Art. 4.4.2.1 / 4.4.3). The validator flags their absence as deviations to correct before execution.
AFDD (2023 Amendments)
The final circuits in bedrooms get an AFDD (arc fault detection device) — a new measure from the 2023 amendments, against fires of electrical origin.
Art. 4.1.5.2.1 — I7-2011 (amended by the 2023 updates, point 12)
“In alternating-current systems, additional protection shall be provided by a residual current device (RCD) not exceeding 30 mA for (per the recommendations of SR HD 60364-4-41): — general-use socket outlets and/or current-using equipment with a rated current not exceeding 32 A; — mobile equipment for outdoor use with a rated current not exceeding 32 A; — for lighting circuits, in single-family dwellings.”
E. Balancing and final validation
Balance the phases (three-phase)
On three-phase installations, distribute the single-phase circuits as evenly as possible across R/S/T, so that the imbalance stays below 15 % (see the “Three-phase balance” page).
Run the validator
At the end, the I7 validator checks the whole project: cross-sections, protections, RCD, voltage drop, balance. You correct the flagged errors down to zero.
Free panel designer
Start from scratch: add circuits, choose the equipment, room, type and cross-section — the I7 validator evaluates in real time
Choose the exercise
The client asks you for:
„I just moved into an apartment and I want the bare essentials: the water heater and the washing machine in the bathroom, plus a socket and a light in the kitchen and in the living room. Set them up on circuits properly.”
To install (checked off as you add circuits):
Design score
17%
Loads covered
1/6
I7 deviations
0
No I7 deviations on the added circuits. Complete all the loads requested by the client to finalize the design.
The validator checks your decisions: minimum cross-section per circuit type (V01), high-power appliances on a dedicated circuit (V04/V40) and the cross-section of three-phase circuits (V20). The panel, the main protection (RCCB 30 mA + SPD) and the connections are generated automatically.
Exercises — choose the correct option
You go through each step by choosing the correct answer. Wrong? Try again.
Design a socket circuit
Kitchen: common socket circuit, 2000 W single-phase (cos φ = 0.95).
Step 1: What is the first step in designing the circuit?
Dedicated or common?
You have a 7 kW electric hob and 4 living room sockets.
Step 1: How do you supply the hob?
Three-phase balancing
Three-phase house with 3 large single-phase loads (of similar power).
Step 1: How do you distribute them across the phases?
Mandatory protections
The main board of a new dwelling.
Step 1: What do you put at the entry against overvoltages (lightning)?
Exercises — you calculate each step
You enter the value for each step yourself. You get hints if you go wrong.
Size the water heater circuit
Water heater 3000 W single-phase (cos φ = 0.95), 30 °C, one circuit, copper.
Step 1: Design current Ib = P / (230 × cos φ) = ?
Washing machine — dedicated circuit
Washing machine 4400 W single-phase (cos φ = 1), 30 °C, one circuit, copper.
Step 1: Design current Ib = P / 230 = ?
How many circuits at minimum
Studio flat with: lighting, common sockets, hob (dedicated), water heater (dedicated).
Step 1: The minimum number of separate circuits = ?
Exercises — direct answer
You solve it on your own and give the final answer. The step-by-step solution is available if needed.
Design current
Single-phase load 2000 W, cos φ = 0.95. What is Ib (A)?
Minimum socket cross-section
What minimum cross-section (mm², Cu) do you give a socket circuit?
Three-phase current
Hob 7200 W three-phase (cos φ = 1). What is Ib per phase (A)?
Discussion
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