Garden Electrical Installation London — BS 7671 Section 705

Garden circuits fall under general BS 7671 rules plus Section 705 (agricultural/horticultural — relevant for greenhouses) and Section 753 (heating cables, e.g. outdoor underfloor).

Every outdoor socket and lighting circuit must have 30 mA RCD protection. Type A RCD required from BS 7671:2018 + A4:2026 (October 2026) where DC fault current is foreseeable.

Fittings must be IP44 minimum for splash-resistance. IP65 for fully exposed locations.

Cable runs underground must be SWA (Steel Wire Armoured) or buried in conduit at minimum 600mm depth.

SWA cable is the workhorse for outdoor circuits. Steel wire armour provides mechanical protection plus an additional earth path.

Typical sizing: 2.5mm² SWA for sockets up to 32A, 4mm² for high-load circuits like EV chargers, 6mm² or 10mm² for sub-mains feeding garden offices.

Burial depth — 450-600mm minimum to BS 7671. Use marker tape 150mm above the cable to warn future excavators.

Glands at every entry/exit — the SWA armour clamps into a gland that bonds the armour to earth. Loose glands are a common EICR finding.

Cost per metre installed: £18-28 for 2.5mm² SWA, £25-40 for 4mm², £40-60 for 10mm². Add £100-200 for trench preparation per 10m run.

A garden office is effectively a new sub-installation. Treat the run as a sub-main feed from the main consumer unit to a sub-board in the office.

Typical sub-main: 10mm² SWA from house consumer unit to garden office sub-board. Feeds a 40-60A circuit.

Sub-board in the office: small 4-6 way consumer unit with RCBOs for lighting, sockets, heating.

Heating in garden offices is usually electric (panel heaters or low-temperature underfloor). Heat pump option for larger offices.

Total cost for a typical 20m² London garden office electrical: £1,800-3,500 including sub-main, sub-board, internal circuits, lighting and certification.

Single outdoor socket on the rear of the house — typical install £180-280. Branch from existing kitchen ring main via a spur and an IP-rated socket.

Outdoor double socket on a free-standing pillar — £350-550 install. SWA run from house, mounted on a small concrete plinth.

Garden lighting — typically low-voltage (12V or 24V) for safety and ease of install. Transformer in the house or in an IP-rated outdoor enclosure.

Mains-voltage garden lighting needs IP65 fittings, SWA cable runs, and proper earth bonding. Use only for accent or pathway lights where low-voltage is impractical.

Driveway-mounted EV charger — typical install. SWA from the house consumer unit, charger pedestal-mounted or wall-mounted on a garden wall.

Detached garage charger — SWA sub-main to the garage, sub-board in the garage with the charger circuit.

Charging cable must reach the car. Tethered chargers (Ohme Home Pro, Hypervolt 3 Pro tethered) are convenient; untethered allows any cable.

Earthing — every EV charger needs Type A RCD or Type B + DC monitoring per Reg 722. On a PME supply, also needs TT earth electrode or DC monitoring.

Cost — £900-1,500 install for a wall-mounted charger 15m from the consumer unit, less the £350 OZEV grant where eligible.

C2 — outdoor socket without RCD protection. Common in pre-2010 installs.

C2 — SWA gland loose or damaged at house entry. Earth bonding compromised.

C2 — cable buried at less than 200mm without conduit. Risk of mechanical damage.

C3 — Type AC RCD on a circuit serving an EV charger. Recommend Type A RCBO.

C3 — outdoor lighting with cable run not protected against UV degradation. Recommend SWA or conduit-protected run.

FI — outdoor circuit termination not visible (e.g. buried junction box). Investigate to confirm safety.