Domestic Wiring Diagram
This is a free printable domestic wiring diagram: download the diagram as SVG or open it and print to paper or PDF.
Understand how a domestic electrical installation is structured, from the supply intake and consumer unit through ring circuits, radial circuits, earthing, and RCD protection.
A domestic electrical installation distributes power from the utility company's supply point to every socket outlet, light fitting, and fixed appliance throughout a home. Understanding how this system is structured — and how each component protects both property and occupants — is essential for anyone specifying, managing, or maintaining residential electrical work.
In the UK, the installation begins at the service head (fuse cut-out), which is owned and maintained by the Distribution Network Operator (DNO). The consumer's cabling then runs through the electricity meter to the consumer unit (CU), also called the fuseboard or distribution board. In most countries, a similar arrangement applies: the service entrance, meter, and main distribution board form the intake section.
In the UK, the standard domestic supply is single-phase 230 V AC, 50 Hz. The consumer unit contains a main isolation switch and individual protective devices — MCBs (Miniature Circuit Breakers) or fuses — for each circuit. Modern consumer units also include at least one 30 mA RCD (Residual Current Device) protecting groups of circuits, or individual RCBOs (combined MCB and RCD) on each circuit.
Domestic circuits in the UK fall into several types. Socket outlet circuits use a ring final circuit topology — the cable runs from the consumer unit, loops through every socket outlet in sequence, and returns to the same consumer unit terminals, creating a ring. This configuration allows each socket to be supplied from either direction around the ring, effectively halving the impedance and doubling the current-carrying capacity compared to a simple radial circuit. A standard UK ring final circuit uses 2.5 mm² flat twin-and-earth cable and is protected by a 32 A MCB.
Lighting circuits are typically wired as radial circuits — the cable runs from the CU to the first light, then to the next, and so on, terminating at the last fitting without returning. Lighting circuits use 1.0 mm² or 1.5 mm² cable and are protected by a 6 A or 10 A MCB.
Fixed appliances such as cookers, showers, and electric ovens are wired on dedicated radial circuits with cable sizes and MCB ratings matched to the appliance's maximum current demand.
All installations must include adequate earthing and protective bonding to prevent dangerous touch voltages on metal parts of the installation and structure. In the UK, main protective bonding connects the incoming water, gas, and oil pipework to the main earthing terminal at the CU using 10 mm² (minimum) green/yellow bonded conductors.
Domestic wiring standards and symbols vary significantly by country. Australian and New Zealand installations follow AS/NZS 3000 (the Wiring Rules) with specific switchboard layouts and circuit arrangements, while UK domestic wiring follows BS 7671 (the IET Wiring Regulations) with ring-main circuits and its own symbol set. Indian students studying domestic wiring for Class 10 science use a simplified model circuit covering a main switch, fuse, energy meter, and parallel branch circuits for lights and fans. You can draw any of these regional layouts free online at circuitdiagrammaker.com.
How to wire domestic wiring diagram
- Understand your supply and earthing arrangement Identify your earthing system: TN-C-S (PME/Protective Multiple Earthing) is the most common in the UK, where the neutral and earth are combined in the distribution network and separated at the service head. TT systems (earth via local earth electrode) are common in rural areas. The earthing system affects how protective bonding and additional earthing is designed — a qualified electrician must assess this.
- Assess the existing consumer unit Determine whether the existing consumer unit has adequate spare capacity for new circuits, whether it contains 30 mA RCD protection for all circuits as required by current regulations (BS 7671:2018+A2:2022), and whether it is in a safe, serviceable condition. Old rewirable fuse boards or split-load boards without RCD protection on all circuits should be considered for replacement when undertaking significant electrical work.
- Plan new circuit routes Plan the cable routes from the consumer unit to each new circuit. Cables must be routed in 'prescribed zones' — within 150 mm of the top of a wall, within 150 mm of the corner of a wall, or horizontally or vertically from an electrical accessory — to protect them from later damage by nails and screws. Alternatively, cables must be in metallic conduit, clipped behind plasterboard with at least 50 mm cover, or at depths established by a cable avoidance tool.
- Size the cable and protective device Select the cable cross-section based on the design current and installation method (e.g., clipped direct, in thermal insulation, grouped with other cables). Then verify the voltage drop from the consumer unit to the furthest point of the circuit does not exceed 3% for lighting or 5% for power circuits. Select an MCB or RCBO with a current rating that does not exceed the cable's tabulated current-carrying capacity.
- Install the cables and accessories Install cables along planned routes, securing with cable clips at intervals specified in BS 7671 (typically 250 mm for horizontal runs, 400 mm for vertical runs of flat twin-and-earth). All cables entering a consumer unit must be identified with a durable circuit label. All terminations must be made in accessible junction boxes or within accessory back boxes — not buried in walls unsupported.
- Connect at the consumer unit With the main isolation switch in the OFF position, terminate new circuit cables at the consumer unit: brown (live) to the MCB or RCBO, blue (neutral) to the neutral bar, green/yellow sleeved earth to the earth bar. Follow the consumer unit manufacturer's maximum torque specifications for all terminal screws — undertightened terminals are a leading cause of arcing and fire.
- Test and certify before energising Perform all required tests in sequence: continuity of protective conductors, ring final circuit continuity (if applicable), insulation resistance (500 V DC), polarity, earth fault loop impedance, and RCD operation. Record all results on an Electrical Installation Certificate (EIC) or Schedule of Test Results. Only energise the new circuits after all tests pass. Notify building control if required by Part P.
Specifications
| Standard UK supply voltage | 230 V AC, 50 Hz (single-phase) |
|---|---|
| Standard UK ring circuit protection | 32 A MCB or RCBO, Type B |
| Standard UK ring circuit cable | 2.5 mm² flat twin-and-earth, BS 6004 |
| Standard UK lighting circuit protection | 6 A or 10 A MCB or RCBO, Type B |
| RCD trip current (all domestic circuits) | 30 mA maximum (BS 7671 regulation 411.3.3) |
| Maximum voltage drop (lighting circuits) | 3% of nominal supply voltage (6.9 V on 230 V) |
| Maximum voltage drop (power circuits) | 5% of nominal supply voltage (11.5 V on 230 V) |
| Main protective bonding conductor minimum size | 10 mm² (TN-C-S / PME systems per BS 7671 Table 54.8) |
Safety warnings
- Domestic electrical installation work in the UK is subject to Part P of the Building Regulations and BS 7671 (IET Wiring Regulations). Work must be carried out by a competent person. In other countries, equivalent regulations apply (NEC/NFPA 70 in the USA, AS/NZS 3000 in Australia/NZ, IEC 60364 internationally). Engaging an unqualified person for notifiable electrical work is illegal and may invalidate buildings insurance and home sale.
- Always isolate the consumer unit main switch and verify the circuit is dead at the point of work using a calibrated voltage tester before touching any conductors. Never work on live circuits.
- The meter tails (cables between the meter and consumer unit) and the service head are owned by the Distribution Network Operator and may only be worked on by an authorised DNO engineer or metering operative. Do not touch these conductors under any circumstances.
- Main protective bonding to gas, water, and oil pipework must be installed and maintained correctly. Missing or disconnected bonding creates a risk of electric shock if a fault energises the pipework.
- Always apply correct torque to consumer unit terminal screws using a calibrated torque screwdriver. Loose terminals are a leading cause of arcing, overheating, and electrical fires — even when connections initially appear secure.
Tools needed
- Insulation resistance tester (Megger or equivalent, 500 V DC)
- Low-resistance ohmmeter or continuity tester
- Earth fault loop impedance tester
- RCD tester (calibrated, 30 mA)
- Calibrated non-contact voltage tester
- Torque screwdriver (for consumer unit terminals)
- Cable detection tool (for locating existing buried cables)
- Wire strippers, side cutters, and screwdrivers
Common mistakes
- Failing to sleeve bare earth conductors in green/yellow insulation at all termination points, leaving the earth conductor indistinguishable from live conductors at a later date.
- Installing socket outlets on a ring circuit using a spur from an existing spur — a spur from a spur is not permitted under BS 7671 and overloads the original socket's wiring.
- Not testing insulation resistance before energising new circuits, missing cable faults or damaged insulation that would cause nuisance RCD tripping or, worse, a fire.
- Burying junction boxes inside wall plaster without providing access, making future fault-finding impossible and creating a non-compliant installation.
- Using the wrong cable size for the installation method — cable clipped in thermal insulation must be derated significantly; using a standard clipped-direct rating in insulation causes the cable to overheat.
- Not labelling circuits at the consumer unit, making future isolation for maintenance or emergency dangerous when the correct circuit cannot be quickly identified.
Troubleshooting
- RCD trips immediately when a specific MCB is switched on
- Cause: Earth fault (insulation breakdown) on that circuit Fix: Isolate the circuit's MCB and disconnect all accessories (sockets, lights) on the circuit. Perform an insulation resistance test at 500 V DC between the live conductor and earth. If the reading is below 1 MΩ, the cable has an insulation fault. Progressively isolate sections of the circuit to locate the fault section.
- Socket outlets on a ring circuit intermittently show no power at one location
- Cause: Broken ring: one section of the ring cable has an open circuit, turning the 'ring' into a radial circuit that overloads the remaining cable Fix: Test ring circuit continuity using the standard BS 7671 ring final circuit test (end-to-end resistance, cross-connected resistance, and Rr/4 method). An open in the ring will be identified by an asymmetric reading when sockets are tested with the ring conductors cross-connected at the CU.
- Lights flicker when high-power appliances are used
- Cause: Excessive voltage drop due to undersized or long wiring; or shared neutral in a system with unbalanced load causing neutral conductor voltage Fix: Measure voltage at the consumer unit and at the flickering fitting under load. Calculate voltage drop. If it exceeds the limits, the circuit cable is undersized for the load or the run length. Also check the neutral conductor terminations at the consumer unit — a loose neutral causes voltage fluctuation on that circuit.
Frequently asked questions
What is the difference between an MCB and an RCBO?
An MCB (Miniature Circuit Breaker) protects against overload current and short circuits — it disconnects when current exceeds its rated value. An RCBO (Residual Current Breaker with Overcurrent protection) combines MCB protection with RCD (earth leakage) protection in a single device. An RCBO disconnects on overcurrent or on a current imbalance between live and neutral exceeding 30 mA, providing both shock protection and overload protection.
Why does the UK use ring final circuits for socket outlets?
A ring final circuit is wired as a continuous loop from and back to the consumer unit. This means each socket has two parallel current paths, each in a different direction around the ring. The ring effectively provides twice the current-carrying capacity of either cable alone, allowing 2.5 mm² cable on a 32 A MCB — a configuration that would be unacceptable on a radial circuit where 2.5 mm² cable is limited to 27 A.
What is the purpose of the RCD in a domestic consumer unit?
An RCD (Residual Current Device) monitors the difference in current between the live and neutral conductors. Under normal conditions, current flowing out equals current returning — the difference is zero. If current leaks to earth through a person or a fault, the difference exceeds 30 mA and the RCD disconnects the circuit within 40 ms, at a level below the threshold for cardiac fibrillation.
What cable is used for domestic wiring in the UK?
The standard domestic cable is flat twin-and-earth PVC-insulated cable to BS 6004. It contains a brown (live) conductor, a blue (neutral) conductor, and a bare copper earth conductor (which must be sleeved in green/yellow when terminated). Common sizes are 1.0 mm² (lighting), 2.5 mm² (socket outlets and ring circuits), 4 mm² and 6 mm² (showers, cookers), and 10 mm² (larger cookers and some shower circuits).
Do I need a permit or inspection for domestic electrical work?
In the UK, most new circuits and consumer unit replacements are notifiable work under Part P of the Building Regulations. Work must either be carried out by a registered competent person (who self-certifies) or be notified to the local authority building control department and inspected. Other countries have equivalent permit and inspection requirements. Consult your local authority before starting any fixed wiring work.
What does a domestic switchboard wiring diagram in Australia look like?
An Australian domestic switchboard diagram shows the main switch (usually a 63 A double-pole isolator), the neutral bar, the earth bar bonded to the MEN (Multiple Earthed Neutral) link, and individual MCBs or RCDs (or RCBO combinations) for each circuit. Circuits typically include a general-purpose outlet circuit (10 A), a lighting circuit (10 A), a stove/oven circuit (20 A or 32 A), and an air-conditioner circuit. All circuits must comply with AS/NZS 3000.
What is a domestic wiring diagram for Class 10?
The Class 10 domestic wiring diagram (Indian school curriculum) shows a simplified household circuit with an energy meter at the supply entry, a main fuse and main switch, and two parallel branches — one for lights and fans, each with its own fuse and switch, and another for high-power appliances (geysers, AC) with separate higher-rated fuses. The key teaching points are parallel connections, the role of fuses as protective devices, and earthing of appliances.
What does a domestic house wiring diagram in the UK look like?
A UK domestic house wiring diagram (to BS 7671) typically shows a consumer unit with a main switch, RCD(s) or RCBO-protected ways, and circuits for ring-main sockets (2.5 mm² cable in a ring from and back to the same MCB), radial lighting circuits (1 mm² or 1.5 mm² cable), a cooker circuit (6 mm² or 10 mm²), shower circuit, and immersion heater circuit. Ring-main circuits are unique to the UK and are not used in most other countries.
What does a domestic switchboard wiring diagram in New Zealand include?
A New Zealand domestic switchboard follows AS/NZS 3000 like Australia and includes a main switch, neutral bar with MEN link, earth bar, and MCBs or RCBOs for each circuit. Typical circuits are lighting (10 A), general-purpose outlets (10 A or 16 A), stove (20 A–32 A), hot water cylinder (10 A), and air conditioning. All socket outlets in NZ must have RCD protection; switchboards installed from 2022 onward must comply with the updated Electrical (Safety) Regulations.
What are the standard UK domestic electrical wiring diagram symbols?
UK domestic electrical symbols follow BS EN 60617 (also used in IET Guidance Note 7). Common symbols include: a circle with a cross for a ceiling light point, a circle with a central dot for a pendant, a rectangle for a socket outlet, a circle in a square for a switched socket, a square with S for a single-pole switch, double parallel lines for a two-way switch, and a rectangle with CB for a circuit breaker. The IET On-Site Guide includes a full symbol reference, and circuitdiagrammaker.com provides a symbol library for drawing these diagrams free online.