House Wiring Simulator — Practice Home Electrical Circuits

The Electrical Wiring Simulator is a hands-on domestic installation trainer. You place realistic components — a consumer unit with breakers, one-way and two-way wall switches, 13 A sockets, ceiling roses, lamp holders and household appliances — onto a workbench, then wire them together with true multicore cables. Each cable end fans out into its individual coloured conductor nodes (brown Line, blue Neutral, green-yellow Earth), exactly like stripping a real cable. Turn the power on and the circuit comes alive: lamps light, fans spin, breakers trip and overloaded cables overheat.

It is built for electrical trainees, vocational students and instructors who want to practise wiring safely before touching real conductors.

• Add a component: tap a palette item to drop it on the board, or drag it straight from the palette to the exact spot you want. Either way you can drag it again on the board to reposition.
• The consumer unit: the Consumer Unit is your origin. Its face is a live meter — a digital display of power (W), voltage (V), current (A) and a load bar — and its three breakers are clickable: tap MAIN to switch the whole supply, the MCB to reset a trip or isolate, and RCD to fit or remove 30 mA protection.
• Protect a section: drop an MCB Breaker in-line on a circuit — it now carries Line and Neutral (Lin/Nin in, Lout/Nout out), switching the Line and passing the Neutral through. Set its rating; it trips if that section is overloaded; tap it to reset. For a cooker or shower use the 45 A Cooker / DP Switch, a double-pole isolator that breaks both poles together.
• Join many wires: use a Connector Block as a distributor — all its terminals are one common node, so you can branch one connection (Line, Neutral or Earth) out to several conductors. Select it and press ↻ Rotate 90° (inspector or toolbar, or R) to turn it to any of four orientations so it lines up neatly with your wiring.
• Add a wire: in the Add Wire panel pick a wire type (single core, Twin & Earth, 3/4/5-core, armoured SWA, flex, power cord…) and a size, then press Insert Wire. It appears with coloured conductor nodes at each end.
• Wire it up: drag a conductor node (the small coloured dot at a cable tip) onto a component terminal to make a connection.
• Join two wires: drag one conductor tip onto another conductor's tip — an insulator connector appears over the splice. Click that connector (or tap either connected conductor) to open the joint again.
• Bend & route a cable: select a cable and grab the round anchor just past either end. Drag it along the cable to extend that side, or drag it sideways (90°) and the cable folds a right-angle corner and continues in that direction — keep dragging and turning to add more corners. Drag the cable body to move the whole run, drag a corner to reshape it (right-click a corner to remove it), and use the ↻ button (or R) to rotate 90°.
• Plug in an appliance: in the Wire Builder pick Power cord — 3-pin plug, add it, and wire its bare end into an appliance's L, N, E. Then drag its moulded 3-pin plug onto a 13A socket — it seats in the face and connects Line, Neutral and Earth automatically. Tap the socket to flip its switch — the red neon glows when it is switched on and live, and the appliance only runs when the socket is on.
• Sockets & junctions: use a single 13A socket, a double socket (two independently switched outlets on one supply — plug an appliance into either face), a fused socket with its own 3/5/13 A cartridge fuse in the live path (it blows before the main breaker on a fault, and you replace it from the inspector), or an unswitched socket (permanently live — for fridges and freezers that must not be switched off). A maintenance-free junction box gives four independent terminals for loop-in lighting (permanent Line, Neutral, switched Line and Earth).
• Quick power cord: instead of dragging a plug in from the palette, select any socket and use its inspector Power cord toggle — a cord appears already seated in the outlet (button reads PLUGGED IN), ready to wire its other end into an appliance. Toggle it off to remove.
• PIR / occupancy sensor: wire L in, N and the switched Load out to a light, then tap the sensor to simulate motion — it switches the load on while motion is detected and shows a motion / no-motion indicator.
• Photocell (dusk-to-dawn) sensor: the opposite of a timer — wire L in, N and the switched Load out, then tap to toggle day / night. It switches the load on automatically when it goes dark and off in daylight (street & security lighting).
• Smoke detector: wire L and N for power (a green LED confirms mains health). Tap it to simulate smoke — it flashes red and sounds; thanks to its battery backup it still alarms with the mains off.
• Switching: choose the right switch for the job — 1-way (on/off), 2-way (a light from two places), an Intermediate crossover switch (drop it between two 2-way switches to control a light from three or more points), or a 2 / 3 / 4-gang switch (one common Line feeding several lights). Tap any switch on the board to operate it.
• Bell push (momentary): a spring-return push that closes COM → L1 only while you press and hold it — the classic doorbell button. Wire the Line through it to a bell or buzzer.
• Rotary dimmer: a resistive dimmer / fan speed controller. Click its ◀ / ▶ sides (or drag the inspector slider) to change the level; the tool computes the series resistance and voltage drop so the lamp visibly dims and draws less power — watch R, V_load and the brightness update live.
• Timer switch (staircase timer): wire L in, N and the switched Load out; tap to run and it holds the load on for a set duration (5–60 s), counts down on its dial, then switches itself off — the landing/corridor light that turns itself off.
• Selector switch: a 3-position rotary that routes the COM input to output 1, 2 or 3 — pick which of several circuits is fed (Manual/Off/Auto, or one of three lamps). Tap to step through the positions.
• Isolator switch: a red rotary double-pole isolator that breaks both Line and Neutral together for safe working — the lock-off point beside an AC unit, boiler or sub-board.
• Generator & changeover (standby power): add a Generator (a second live source — tap to start it) and a Changeover Switch. Wire the consumer unit into the changeover’s Mains side and the generator into its Gen side, then select MAINS / OFF / GEN. On GEN the load runs from the generator — switch Power OFF to simulate a mains failure and watch the generator keep it alive (generator-fed loads are metered on the generator, not the consumer unit).
• Surge Protection Device (SPD): a Type-2 device wired in parallel across L, N and E at the consumer unit. It sits idle in normal use and diverts surges to earth; its window shows green (healthy) or red (end-of-life). Land the incoming L/N/E on it and continue them onward.
• Emergency light: a non-maintained fitting — wire its permanent L and N. While the Line is live the battery charges and the lamp stays off (green LED); the moment the Line loses power (a cut, an upstream trip, or Power OFF) it fires its LED from the internal battery automatically.
• Energise: press Power ON. Toggle switches by tapping them.
• Edit tools (bottom of the canvas): Undo, Redo, Duplicate, Rotate cable, Delete and Clear.
• Multimeter (debug tool): click the meter button in the canvas toolbar (next to Duplicate) to bring up a floating multimeter. Drag its body anywhere, and drag the red and black probes onto any terminals or conductor tips — they clamp on like a connection. Switch between V (voltage between the two points), A (current — the correct way is to clamp one probe onto a wire to read the current it carries without breaking anything, or to break the Line and insert the meter in series so the load is fed through it. Just like a real ammeter, clipping both probes straight across a live pair — Line to Neutral, or across a running appliance — is a dead short, so the meter flashes a shorted! warning instead of a reading) and Ω (continuity — beeps when the two points are on the same net, and works with the power off). Read L–N = 230 V, 230 V across an open switch, 0 V across a closed one, and the live current in any cable. Close it with the meter button again or the × on the meter.
• Resize a component or load: select it and drag the round grip on the bottom-right corner of its outline to scale it between its full size and a compact minimum — every detail stays readable and every switch stays tappable even at the smallest size. You can also set an exact size with the Size slider in the inspector, or right-click and pick Minimum / Maximum size.
• Right-click for quick actions: right-click any item for a menu — Properties, Minimum / Maximum size, Duplicate and Remove for that item, plus Save as Image, Copy Reading and Clear Board.
• Double-click to edit properties: double-click a component, load or cable to open its Properties pop-up — the very same controls as the side inspector (rating, fuse, wattage, state, size). Changes apply live as you make them; press OK to close, or Delete to remove the item.
• Left panel: the Selected Item inspector sits at the top and opens automatically when you select something on the board (and folds away when nothing is selected). Below it the palette is split into industry-standard functional groups — Supply & Protection, Switching & Control, Sockets & Outlets, Connections & Junctions, Sensors/Safety/Emergency, then the load groups Lighting, Motors & Appliances and Heating & High-power. Click any heading to fold that group away.
• Keyboard: Ctrl+Z undo, Ctrl+Shift+Z (or Ctrl+Y) redo, Ctrl+D duplicate, R rotate a selected cable, Delete delete (Shift+Delete clears the board), P power, G generate.
• Save / Open: use Save to download your circuit as a .json file and Open to load one back later — handy for sharing or resuming work.
• Your work is kept automatically: the board is saved in your browser as you go, so if you close the tab or refresh by accident it comes back exactly as you left it — you’ll see “Restored your last circuit”. Opening a shared link always takes priority over the saved board, and nothing is ever uploaded — it stays on your own device.
• Fullscreen: the Fullscreen button (or F) expands the workbench to fill the screen.
• Examples: pick a circuit from the Load an example menu and it loads instantly, fully wired, for you to study or modify.
• Tip banner: the banner across the top of the board explains the loaded example. Your first click on the canvas tucks it away behind a small ℹ info button in the top-left corner — click that button any time to read the tip again (loading a new example brings it back).

Simulate is the wiring workbench. The toolbar gives you Power, an example-circuit menu, a 230 V / 120 V supply toggle, and Save / Open / Fullscreen; the in-canvas tools handle undo, redo, duplicate, rotate, delete and clear. The readout badges show supply voltage, total load current, how many loads are live, and overall status. The fault strip lists any wiring problems it detects:

• Overloaded cable — current exceeds the cable's rating; it heats up and, if the protective device is too big, catches fire. Both the Line and the Neutral conductors carry the load current, so an undersized neutral overheats too.
• Breaker tripped — overload (thermal, after a short delay) or a Line-Neutral short (instant magnetic trip). On a short the nearest protective device operates: a plug fuse or spur fuse blows before the main breaker trips (discrimination).
• Earth fault — Line touching Earth trips the 30 mA RCD; with no RCD fitted, the heavy fault current trips the breaker instead, and the tool explains why an RCD would be safer.
• Neutral–Earth fault — a Neutral connected to Earth trips the RCD as soon as a load draws current; without an RCD it goes unnoticed, which is exactly why it is dangerous.
• Reversed polarity — a load wired with Line and Neutral swapped still runs (AC does not care), but the tool flags it as a danger: the appliance's own switch and fuse end up in the Neutral.
• Missing earth — a metal-bodied (Class I) appliance with no protective earth is a shock hazard.
• Switched neutral — the switch breaks the neutral instead of the line.
• Wrong / blown plug fuse — every 3-pin power cord carries its own BS 1363 plug fuse (3, 5 or 13 A, set in the cable inspector). A fuse bigger than the flex is flagged; a sustained overload blows the fuse, and you replace it from the inspector.
• Socket overloaded — sockets are rated 13, 16 or 32 A (set in the inspector). Draw more than the rating through a socket and its contacts overheat — fit a 32 A socket, or feed fixed heavy loads like a water heater through a Fused Spur (fuse options now up to 32 A).
• Volt drop too high — a long or undersized run can be fine on current yet drop too much voltage. Each cable models mV/A/m; select a cable to set its length and read the live volt drop, and every appliance shows the total drop back to the consumer unit. The tool warns when a run exceeds the 3 % (lighting) / 5 % (power) limit.

In a ring final circuit the readouts show the current genuinely dividing between the two legs of the ring — the shorter leg carries proportionally more — so you can see why a ring lets a 2.5 mm² cable serve a 32 A breaker.

Real installations use multicore sheathed cable, not loose wires. The Add Wire panel lets you choose:

• Domestic types: single-core (individual Line, Neutral or Earth conductors — as used in conduit/trunking or for earth bonding), 2-core (Line + Neutral), Twin & Earth (+ bare earth), 3-core + earth (for two-way switching), 2-core / 3-core flex for appliances, and the Power cord — 3-pin plug (a flex ending in a moulded BS 1363 plug you drag into a socket).
• Industrial types: SWA armoured (steel-wire-armoured sub-main / underground cable, drawn with its armour), and three-phase 4-core (L1 L2 L3 + N) and 5-core (L1 L2 L3 + N + E), plus 4-core / 5-core flex for three-phase motors and machines. Phase cores use the harmonised brown / black / grey colours.
• Size: metric mm² from 1.0 up to 16 and 25 mm² (sub-mains) or the equivalent SWG number, each showing its current rating. Pick a size whose rating exceeds the load current from I = P / V.

The golden rule the simulator grades against is I_load ≤ I_device ≤ I_cable: the fuse or breaker must be bigger than the running current but smaller than the cable rating.

Current rating is only half the job — a cable must also keep voltage drop in check. Every size carries its mV/A/m figure; select a cable to set its run length (or let it estimate from the route) and read the live V drop and %, with the whole-circuit drop shown at each appliance. Keep it under 3 % for lighting and 5 % for power — a long run may pass on current yet fail on volt drop, which is exactly when you step up a cable size.

Explore organises the theory into four categories: Wire & Cable (SWG, mm², ratings, core colours), Components (switches, sockets, consumer unit, FCU), Protection & Safety (MCB, RCD, earthing, fuses) and Circuits (one-way, two-way, ring/radial, loop-in). Each card has a clear explanation and, where relevant, a worked example.

Practice mode mixes calculation problems (find the load current, pick the cable, size the fuse) with wiring-choice questions. Type or choose your answer, press Check, and read the worked solution. Your score is tracked.

Quiz mode presents 5 questions on cable sizing, colours, switching and protection, then gives a score with a star rating and a per-question breakdown.

Test mode runs the electrician's initial-verification suite on the circuit you built: earth (CPC) continuity, polarity, insulation resistance, earth-loop impedance Z_s (with an adjustable external Z_e) and RCD operation — each with a pass/fail against the BS 7671 limits. Dead tests don't need the power on; Z_s and RCD are live tests.

Every current in the tool comes from I = P / V. Example: a 2000 W heater at 230 V draws 2000 / 230 ≈ 8.7 A, so a 1.5 mm² flex (16 A) with a 13 A plug fuse is safe. The same heater on a US 120 V supply would draw 16.7 A — nearly double — which is why the 120 V toggle recomputes every current.

Safety: all current ratings here are teaching nominals. Real installations must be sized and derated per BS 7671 / local code. This simulator is an educational aid, not a substitute for a qualified electrician.