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)
Engine recommendation (calc-engine)
Design current Ib
9.2 A
Recommended cross-section
1.5 mm²
MCB
10 A · C
Factor K (K1×K2)
1
Calculat cu motorul real al aplicației (calc-engine): Ib din putere, secțiunea cu marja 1.25 și factorii K, disjunctorul din seria standard — aceleași funcții pure folosite și de testele Vitest.
The verdict applies exactly the validator’s condition Ib ≤ In ≤ Iz (V06), over the cross-section recommended by the engine. Change your choices and watch it go from non-compliant to compliant.
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 9 circuits to add for a complete recipe.
Calculation assumptions and scope
- The app’s real engine: the calculations come from `calc-engine` (calcCurrent, recommendCable, recommendBreaker) — the same functions used by the editor’s automatic sizing and by the Vitest tests
- The cross-section is chosen with a 1.25 safety margin (IEC 60364-5-52) and the correction factors K1 (temperature) × K2 (grouping); the MCB = the first standard rating ≥ Ib
- 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
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 margin and K factors
Iz_table × K1 × K2 ≥ Ib × 1.25
Design current = Ib × 1.25 = 17.2 A. The first cross-section with Iz ≥ 17.2 A (at K = 1) is 2.5 mm² (Iz 18 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 ≤ 18 ✓.
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
Sockets and bathrooms are protected by an RCD with ≤ 30 mA; the main board gets a type 2 SPD against overvoltages. Without them, the project does not pass validation.
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
“In alternating voltage systems, additional protection must be provided by a residual current protective device (RCD) not exceeding 30 mA for ... general-use socket-outlets with a rated current not exceeding 20A ...”
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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