Why does my garden lighting RCD keep tripping?

The most common causes are water ingress into a connector or fitting, a damaged cable where it has been cut by a spade, or a faulty driver in one of the fittings. Disconnect each fitting in turn to identify which one is the source.

Can I bury garden lighting cable without conduit?

Low-voltage cable for 12 V garden lighting systems can be buried without conduit at 300 mm depth, but a 230 V mains run to a garden lighting circuit must use SWA armoured cable or be in conduit and buried at 500 mm. Either way, mark the route before you bury it.

Do garden lights need an RCD?

Yes. BS 7671 Regulation 411.3.3 requires 30 mA RCD protection on all outdoor socket and fixed equipment circuits. A 30 mA RCBO or RCD in the consumer unit covers the garden lighting circuit.

How to Fault-Find Garden Lighting (UK)

Helpful video reference. We use Cory and Oscar from Electrician Life's garden lighting fault-finding video as the video reference here. It is a real UK domestic job filmed start to finish, which is rare. Watch it before you start so you know what to expect at each stage.

Before you start. Garden lighting runs on a live 230 V supply from the consumer unit, even if the fittings themselves are 12 V. Always isolate at the consumer unit and confirm dead with a voltage tester before opening any junction box or weatherproof connector outdoors. Do not assume a tripped breaker means the circuit is safe elsewhere.

1. Start at the consumer unit

Look for a tripped RCBO or the RCD section that covers your garden circuit. A tripped RCBO sits visibly between on and off. Try resetting it: if it holds, you may have had a temporary fault (a slug crossing a connector, most likely). If it trips again immediately, leave it off and keep going.

If the MCB and RCD are both showing on and the lights are still dead, the fault is downstream, not at the board.

2. Check the fused connection unit

Most garden lighting circuits are fed via a fused connection unit (FCU) inside the house, garage or outbuilding. Check that it is switched on, then remove the fuse carrier and test the fuse with a continuity tester. A 3 A fuse is typical for LED garden lighting; a blown fuse means excess current was drawn somewhere on the run.

If the fuse is fine and the FCU is switched on, use a voltage tester at the load terminals of the FCU to confirm supply is arriving. No supply here points back to the board or the cable between them.

3. Test at the first outdoor fitting

With the circuit live, use a non-contact voltage tester at the first fitting in the run. Presence of voltage here tells you supply is reaching the garden. Dead here means the cable from the FCU to the first fitting is broken or the connection at the FCU load terminals is loose.

The cable from the FCU into the garden is usually armoured SWA or 1.5 mm twin and earth in conduit. If it is plain twin and earth directly buried with no protection, note this for the report.

4. Work along the run fitting by fitting

Garden lighting runs are almost always daisy-chained: supply arrives at fitting 1, a cable loops to fitting 2, another to fitting 3, and so on. If fitting 1 is live but 2 and 3 are dead, the cable between fittings 1 and 2 is where the fault lies, or the in-line connector between them has failed.

Test at each fitting in sequence until you find the last live one. The fault is between that fitting and the next dead one.

5. Open and inspect outdoor connectors

Outdoor cable connectors take a beating from frost, rain and UV. Open the connector between the last live fitting and the first dead one. Look for:

Green corrosion on the terminals or conductors
Water pooled inside the connector body
A conductor that has pulled back out of its terminal
A conductor that has corroded and snapped just inside the insulation

If you find any of these, dry the connector with a cloth, cut back the conductor to clean copper, re-terminate in a new IP67-rated weatherproof connector, and retest. Many garden lighting faults end here.

6. Test the fittings and lamps

If supply is present at a fitting but it does not light, swap the lamp for a known-good one first. LED garden lamps can fail silently. If a good lamp does not light, the driver inside the fitting has failed. Most driver failures in garden lights show as nothing: no light, no noise, no heat. Replace the fitting or the driver, if it is a separate part.

Some garden fittings use a 12 V transformer or driver shared across a small cluster of lights. A failed transformer takes out every fitting on its output. Test the transformer secondary output with a multimeter on AC volts. If it reads 0 V with supply present at the primary, replace the transformer.

7. Underground cable damage

If you have traced the fault to a section of cable that is buried and the RCD trips the moment you try to energise it, the cable has been cut through or crushed. This is a job for an electrician: the buried section must be replaced with correctly rated armoured cable and buried at the right depth with cable protection tiles above it. Do not try to splice into buried cable without proper waterproof jointing boxes.

Stop and call an electrician if: the RCD trips immediately on reset and will not hold, you find the buried cable has been cut or damaged, there is visible scorching around any fitting, the cable run is unarmoured twin and earth buried directly in soil, or any conductor has fabric or rubber insulation indicating very old wiring.

When to call us

Underground cable replacement and any new outdoor circuit work is Part P notifiable. In Sandwich, Richard can run a new SWA cable, install the right connectors and certify the work for less than you might expect. Small fault-finding visits are £10 per 10 minutes.

Garden lighting fault in Sandwich?

Richard diagnoses outdoor electrical faults efficiently and carries the right connectors and fuses on the van.

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How to fault-find garden lighting