Shed Wiring Diagram

Shed Wiring Diagram — interactive diagram. Open it in the editor to customise components and wiring.

This is a free printable shed wiring diagram: download the diagram as SVG or open it and print to paper or PDF.

Plan a safe, code-compliant shed electrical installation with correct SWA cable submains, consumer unit sizing, RCD protection, earthing, and outdoor-rated enclosures.

Wiring a detached shed, workshop, or outbuilding is one of the most commonly misunderstood domestic electrical projects. It is not simply a matter of running an extension lead from the house — a permanent electrical installation in a separate structure must comply with the wiring regulations applicable in your country (BS 7671 in the UK, NEC/NFPA 70 in North America, AS/NZS 3000 in Australia and New Zealand, or IEC 60364 elsewhere) and must be inspected and certified by a competent person or licensed electrician.

The submain cable — the cable running from the main consumer unit (CU) in the house to the shed — must be suitable for the installation method. For underground runs, Steel Wire Armoured (SWA) cable is the standard choice in the UK and many other jurisdictions: the armour provides mechanical protection against accidental damage from digging and acts as an earthing conductor. The cable must be buried at a minimum depth of 500 mm under domestic garden areas (450 mm under concrete), with a cable route marker tape laid 150–200 mm above it to warn future excavators.

Alternatively, the cable can run overhead if the span is short enough to avoid excessive sag and clearance requirements are met (typically 3.5 m minimum above ground level for pedestrian access, 5.2 m for vehicular access per BS 7671). Overhead runs generally require a catenary support wire to carry mechanical load.

At the shed, a dedicated consumer unit with a main switch and at least one RCD (or RCBO protection on individual circuits) is essential. The shed CU should be fed via a separate way in the house CU, with a fuse or MCB rated for the submain cable capacity. In the UK, shed circuits must include 30 mA RCD protection throughout (BS 7671 regulation 411.3.3).

Earthing of the shed requires careful consideration. If SWA cable is used and the armour is correctly terminated into both CUs, the armour provides the circuit protective conductor (CPC). An additional earth rod at the shed is required if the shed is supplied by TT earthing or if the design calls for a separate installation earth. An earth electrode resistance test should be performed and recorded.

A shed wiring diagram needs to cover the supply method (underground SWA cable or overhead), a small consumer unit inside the shed, and the individual circuits for lighting and sockets. UK installations must comply with Part P of the Building Regulations, meaning all shed sub-circuits require RCD protection and correct cable sizing. You can plan the full layout — from the house distribution board to the shed consumer unit and each final circuit — using the free browser-based wiring diagram editor.

How to wire shed wiring diagram

Calculate the shed's maximum electrical demand List every load to be installed: lighting (LED panels are typically 10–40 W each), power sockets (plan for tools that may draw 1000–3000 W), and any fixed equipment (heaters, compressors, EV chargers). Apply diversity factors per your applicable standard (e.g., BS 7671 Appendix 1 in the UK) to calculate the design current. This determines the submain cable size and the main fuse or MCB rating.
Select and size the submain SWA cable Select a cable current rating that exceeds the design current, then check that voltage drop from the house consumer unit to the furthest point in the shed does not exceed 3% of nominal voltage (approximately 6.9 V on a 230 V system). Adjust cable size upward if voltage drop is excessive. Confirm the cable is suitable for the installation method (direct burial, duct, overhead).
Prepare the cable route For underground routes: dig a trench at least 500 mm deep. Lay a 50 mm bed of sand or soft sieved soil in the bottom of the trench. Route the SWA cable along the bottom, avoiding sharp bends tighter than the cable's minimum bending radius. Lay cable route marker tape 150–200 mm above the cable before backfilling with sand, then with excavated soil.
Terminate the SWA cable at the house consumer unit Use a suitable SWA cable gland to terminate the cable into the house consumer unit enclosure (or into an IP-rated junction box feeding the CU). Correctly terminate the armour using the inner gland collar. Connect the conductors to a spare way in the CU — phase to a suitably rated MCB, neutral to the neutral bar, and armour/CPC to the earth bar. The way's MCB rating must not exceed the cable's current-carrying capacity.
Install the shed consumer unit Mount a suitable consumer unit inside the shed in a dry location. The CU must include a main isolator and at least one 30 mA RCD (or RCBOs for individual circuits). Terminate the incoming SWA: phase to main switch input, neutral to neutral bar, armour/CPC to the earth bar. Install MCBs or RCBOs for each circuit — typically a 6 A for lighting and 16 A or 20 A for socket outlet circuits.
Install circuits, sockets, and luminaires Wire the shed circuits using standard cables (1.0 mm² for lighting, 2.5 mm² for socket outlets in the UK) in surface-mounted conduit or trunking, or flush-mounted in the structure. Use outdoor-rated sockets with IP ratings appropriate for the shed environment (IP44 minimum for dusty workshop environments, IP55 for exposed locations).
Test, inspect, and certify Before energising: perform insulation resistance tests, continuity of protective conductors, polarity checks, and earth electrode resistance measurement if an earth rod is installed. After energising: test RCD operation with a calibrated tester. In the UK, issue an Electrical Installation Certificate (EIC) or Minor Electrical Installation Works Certificate (MEIWC) as appropriate. Notify building control if required by Part P.

Specifications

Minimum burial depth (garden areas, UK)	500 mm under BS 7671 / IET Guidance
Maximum voltage drop (origin to furthest point)	3% of nominal supply voltage (6.9 V on 230 V system)
RCD trip current (socket outlet and all shed circuits)	30 mA maximum per BS 7671 regulation 411.3.3
Minimum overhead cable clearance (pedestrian)	3.5 m above ground level (BS 7671)
Minimum overhead cable clearance (vehicular)	5.2 m above ground level (BS 7671)
Cable route marker tape depth above cable	150–200 mm
SWA cable rating standard (UK)	BS 5467 (XLPE insulated) or BS 6724 (LSF sheathed)
Minimum IP rating for outdoor sockets in exposed locations	IP44 (splash-proof); IP55 recommended in exposed conditions

Safety warnings

Shed electrical installations are permanent fixed wiring and must be designed, installed, inspected, and certified by a licensed electrician in accordance with the wiring regulations applicable in your country (BS 7671 in the UK, NEC/NFPA 70 in North America, AS/NZS 3000 in Australia/NZ, IEC 60364). In the UK, new circuits from the house are notifiable under Part P of the Building Regulations.
Always isolate and lock-off the circuit at the house consumer unit before working on any part of the shed electrical installation. Verify the circuit is dead using a calibrated voltage tester at the point of work — not just at the CU — before touching conductors.
Underground SWA cable can be damaged by future digging if not properly protected and marked. Always lay cable route marker tape and keep an accurate record (scale drawing) of the cable route for future reference.
RCD protection at 30 mA is mandatory for all socket outlet circuits in a shed under most modern wiring regulations. Never bypass or omit RCD protection — it is the primary defence against electric shock in an environment where power tools and damp conditions frequently occur together.
If the shed has a metallic structure (steel frame, metal roof sheeting), equipotential bonding of all exposed metalwork to the main earthing terminal is required. Consult a licensed electrician to assess bonding requirements specific to your installation.

Tools needed

Insulation resistance tester (Megger or equivalent)
Continuity tester and low-resistance ohmmeter
RCD tester (calibrated)
Earth electrode resistance tester
Cable stripper and SWA armour cutter
Cable gland spanner set
Trenching spade and sand bedding material
Spirit level and drill with masonry bits

Common mistakes

Using standard PVC twin-and-earth cable for the underground run instead of SWA cable, which leaves the cable vulnerable to mechanical damage and moisture ingress.
Failing to notify building control or use a registered competent person for the work, creating an unverified installation that could affect home insurance and property sale.
Burying the cable too shallow (under 500 mm), making it vulnerable to damage during routine garden work.
Not installing a separate consumer unit in the shed — instead, running long extension leads or multiple socket adapters — creating a fire and shock risk.
Omitting the earthing termination of the SWA armour at one or both ends, leaving the armour unbonded and the installation without a continuous circuit protective conductor.
Failing to measure and record earth electrode resistance where an earth rod is installed, leaving no verification that the earth impedance is low enough for protection to operate.

Troubleshooting

RCD at the shed consumer unit trips immediately on energising: Cause: Insulation fault on a shed circuit, or conductor damaged during cable installation Fix: Isolate all MCBs at the shed CU. Energise the RCD with all MCBs off: if it holds, switch each MCB on one at a time to identify the faulty circuit. Perform an insulation resistance test on the faulty circuit with a 500 V DC insulation tester to locate the fault.
Lights or sockets work intermittently or voltage is low at the shed: Cause: High resistance in the submain cable run — corroded connections, undersized cable, or damaged SWA armour creating a partial short Fix: Measure the voltage at the house CU and at the shed CU under load. Calculate the actual voltage drop. If it exceeds 3% of nominal, check all terminations for tightness and corrosion. Perform a resistance test on each conductor of the submain cable.
Earth continuity fails between house earth bar and shed earth bar: Cause: SWA armour not properly terminated into both cable glands, or armour conductors not connected to earth bars Fix: Inspect both SWA cable glands for correct armour engagement. Measure resistance between the house earth bar and the shed earth bar — it should be less than 1 Ω. Recheck inner gland collar engagement on the armour wires and all earth bar connections.

Frequently asked questions

Does shed wiring need to comply with building regulations or be inspected?

In the UK, adding a new circuit from the house to a shed is notifiable work under Part P of the Building Regulations. This means it must either be carried out by a registered competent person or be notified to the local authority building control and inspected. Other jurisdictions have equivalent permit and inspection requirements. Check with your local authority before starting.

Can I use a standard PVC cable underground from the house to the shed?

Standard PVC twin-and-earth cable (BS 6004) is not rated for direct burial underground. It lacks mechanical protection and has insufficient UV and moisture resistance. Use SWA (Steel Wire Armoured) cable to BS 5467 or BS 6724 for underground runs, or enclose PVC cable inside appropriate conduit (heavy-gauge rigid PVC or galvanised steel) buried at the required depth.

What size cable do I need for a shed supply?

Cable size depends on the maximum load (watts), the cable run length (voltage drop), and the installation method (burial depth, grouping with other cables). A typical domestic shed with lighting and a few power sockets will work on 2.5 mm² SWA for runs under 25 m. A workshop with heavy machinery may need 6 mm² or 10 mm² SWA. Calculate maximum demand, then calculate voltage drop — it must not exceed 3% of supply voltage from origin to furthest point.

Do I need an earth rod at the shed?

It depends on the earthing system. If the supply is via SWA cable with the armour correctly terminated as the CPC, an earth rod is not mandatory. However, for TT earthing arrangements, or where an additional earth electrode is specified by the design (e.g., for equipotential bonding in a workshop with metallic structures), an earth rod is required. The earth electrode resistance must be measured and recorded.

How deep must I bury the underground cable?

In the UK under BS 7671 and the IET Guidance Note 1, SWA cable buried under domestic garden areas should be at minimum 500 mm deep, and under areas subject to excavation (e.g., adjacent to driveways or vegetable plots) 600 mm is recommended. Cable route tiles or marker tape should be laid 150–200 mm above the cable. Regulations vary by country — always consult local requirements.

What should an electrical wiring diagram for a shed include?

A shed electrical wiring diagram should show the supply cable route from the main house consumer unit (typically 2.5 mm² twin-and-earth in conduit or armoured cable buried at the correct depth), a small shed consumer unit with an RCD or RCBO, a lighting circuit, and a socket ring or radial circuit. Earth bonding for metalwork and a main switch should also be shown. Clearly labelling cable sizes and MCB ratings makes the diagram useful for both installation and inspection.

What are the UK wiring requirements for a shed electrical wiring diagram?

In the UK, shed wiring falls under BS 7671 (IET Wiring Regulations) and is a notifiable Part P work if it involves a new consumer unit. The supply must be RCD-protected, the underground cable must be armoured (SWA) or in conduit at a depth of at least 450 mm under a path or 600 mm in open ground, and all accessories must be IP-rated if exposed to moisture. A UK shed wiring diagram should also show the main bonding conductor connecting the shed CU earth to the house earth electrode.