How to install garden lighting safely

Helpful video reference. The video above is "Installing Lights In The Garden" from the Electricians Life UK channel, published in January 2023. It shows a UK domestic electrician installing garden spike lights with outdoor-rated fittings and proper weatherproof connections, which is a good practical view of what the work looks like on site.

1. Decide on the supply

There are three realistic options for a UK garden lighting installation:

• Plug-in transformer into an existing outdoor socket. The easiest and safest DIY route. The transformer steps the voltage down to 12 V or 24 V and the low-voltage cable runs to the spike or path lights. The socket must be on a 30 mA RCD circuit. No notifiable work involved.
• Spur from an existing indoor or outdoor circuit. Adding an outdoor lighting circuit as a spur from an existing socket ring is possible, but connecting it at the consumer unit end and running cable outdoors is Part P notifiable work.
• New dedicated circuit from the consumer unit. The cleanest solution for a larger garden lighting scheme. Requires a registered electrician to install the circuit, RCBO protection and Part P certification.

For most homeowners, option 1 (low-voltage plug-in transformer) is the most practical. For anything wired directly at 230 V, call an electrician.

2. Choose the right fittings for outdoors

IP ratings matter outdoors. The IP number tells you how well the fitting is sealed against dust and water. For UK garden use:

• IP44: Minimum for outdoor fittings in a covered or sheltered position (under a pergola, porch soffit or canopy). Protects against water splashing from any direction.
• IP65: Suitable for exposed positions that see direct rain. Required for spike lights and path lights set into damp ground.
• IP67 or IP68: Submersible or near-submersible. Required for in-ground or pond fittings.

Check the IP rating on the fitting datasheet, not just the packaging. Some fittings claim "outdoor use" on the box but carry an IP44 rating that is not adequate for open exposure. LED spike lights in the UK most commonly need IP65.

3. Check and confirm RCD protection

Before connecting any outdoor electrical fitting, confirm the supplying circuit is on a 30 mA residual current device. On a modern RCBO consumer unit, individual circuits have their own RCD protection. On an older split-load board, outdoor circuits should be on the RCD side. On a very old board with a single RCD or no RCD at all, this is a conversation to have with an electrician before proceeding.

Test the RCD using the test button on the device (monthly is good practice, but test it now before connecting outdoor equipment). The board should trip instantly when the button is pressed. If it does not, do not use that circuit for outdoor work until the RCD is repaired or replaced.

4. Plan and mark the cable route

For a transformer-fed low-voltage system, the 12 V or 24 V cable runs from the transformer to each light. Low-voltage cable of this type does not need to be buried deeply or in conduit (it carries too little voltage to be dangerous if cut), but it should be secured out of the way of lawnmowers and garden tools. Cable clips along a fence base or a shallow trench of around 100 mm is typical.

For a mains (230 V) cable run underground, the requirements are stricter. Use SWA (steel wire armoured) cable of the correct cross-section for the load and run length. Bury at least 500 mm deep in garden areas that might be dug over, 600 mm under driveways or paths. Place cable warning tape in the trench above the cable before backfilling.

Avoid burying cable under areas where trees may be planted or where significant digging is expected. Mark the cable route on a sketch and photograph the trench before filling it.

5. Connect fittings in weatherproof enclosures

Every connection and joint in an outdoor electrical installation must be in an IP-rated enclosure, never made in open air or buried in soil. For garden lighting this typically means a weatherproof junction box (Wiska boxes are a common choice on UK installations) at each branching point, with appropriate Wago connectors or screw terminals inside.

At each spike or path light fitting, follow the manufacturer's instructions for connecting the supply leads. Use the correct cable gland where the cable enters the fitting, and tighten it to seal around the cable. A loose gland lets water track along the cable into the fitting.

For low-voltage systems fed by a transformer, connections are at the transformer output terminals and at each fitting. The transformer itself plugs into the indoor or outdoor socket and must be weatherproof if it is going to be exposed to the elements.

6. Test before backfilling, then commission

Before backfilling any cable trench, test the circuit. For a mains installation: test for correct polarity (L and N the right way round), continuity of the protective conductor, and insulation resistance between the conductors. These require a multifunction tester and should be done by whoever is doing the Part P work.

For a low-voltage plug-in system, plug the transformer in, switch on, and verify every fitting works before covering any cable runs. Faults are obvious now and invisible once the garden is back to normal.

Set any dusk-to-dawn sensor or timer on the transformer according to the manufacturer's guide. Most have a simple dial or app. Get the on and off times set correctly before the first evening, otherwise you may find the lights running during the day.

When to call us

Richard installs outdoor socket circuits, garden lighting supplies and exterior light fittings across Sandwich and east Kent. If you want a properly wired outdoor lighting scheme with Part P certification, get in touch for a quote.