Why have my garden lights stopped working?

The most common causes are: a tripped RCD or MCB at the consumer unit, a failed transformer (for low-voltage systems), damaged cable (cut during gardening or gnawed by animals), failed lamp or lamp holder, or water ingress into a fitting that is not rated for outdoor use. Check the consumer unit first — if the outdoor circuit breaker or RCD has tripped, reset it carefully and observe. If it trips again immediately, there is a fault to earth that requires an electrician.

Do garden lights need RCD protection?

Yes. BS 7671:2018+A4:2026 requires 30mA RCD protection on garden lighting circuits under two regulations: Regulation 411.3.4 mandates additional RCD protection (IΔn not exceeding 30mA) for all AC final circuits supplying luminaires in domestic premises — this covers hard-wired garden lighting circuits directly. Regulation 411.3.3 separately requires 30mA RCD protection for socket-outlets rated up to 32A, covering outdoor sockets that feed plug-in garden lighting. This is not optional — it is a requirement under the wiring regulations and is also a condition of Part P Building Regulations compliance. If your garden lighting circuit does not have RCD protection, it is a potentially dangerous (C2) finding that should be rectified by a qualified electrician.

What IP rating do garden lights need?

Garden lights must have an appropriate IP rating for their location. The minimum for a sheltered porch or covered outdoor area is IP44 (protected against splashing water from any direction). For lights fully exposed to rain, the minimum is IP65 (dust-tight and protected against water jets). Lights used in or near water features (ponds, fountains) require IP67 or IP68 (protected against temporary or permanent immersion). Using an indoor-rated light outside will cause rapid failure and creates a safety hazard.

Why does my garden lighting transformer hum?

A slight hum from a magnetic (toroidal) transformer is normal. A loud buzzing or vibrating hum indicates the transformer is overloaded (too many lamps connected), a lamp has partially failed causing high current draw, or the transformer is failing. Check the total wattage of connected lamps against the transformer rating. If the transformer is overloaded, reduce the number of lamps or upgrade to a higher-rated transformer.

How deep do garden lighting cables need to be buried?

Under BS 7671 (Regulation 522.8.10), buried cables in gardens must be installed at sufficient depth to avoid foreseeable damage from ground disturbance. BS 7671 does not prescribe a single fixed figure for all situations — the required depth depends on the type of mechanical protection used and the assessed risk of excavation. Unprotected cables require greater depth than cables within armoured sheaths (SWA) or protective conduit, which offer additional mechanical protection and may permit shallower installation where the local risk is assessed as acceptable. Cable route records (sketch or photograph) should always be provided to the customer to prevent future accidental damage.

What should I do if a garden light fitting fills with water?

Switch off the circuit at the consumer unit immediately. Allow the fitting to dry out completely (at least 48 to 72 hours in a warm, dry environment) before attempting to power it again. Check the IP rating of the fitting — if it is not rated for outdoor use, replace it with a correctly rated fitting. Inspect the fitting for cracks, failed gaskets, or poorly sealed cable entries. Even if the fitting dries out and works, degraded insulation from water ingress will eventually cause an earth fault and RCD tripping.

FAULT FINDING GUIDE

Garden Lighting Not Working: Outdoor Electrical Fault Finding

Complete fault finding guide for garden and outdoor lighting — RCD protection requirements under BS 7671, IP ratings explained, RCD tripping diagnosis, cable damage, transformer faults, waterproofing failures, and typical repair costs for 2026.

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12 min readUpdated 2026-06-10Andrew Moore, Founder of Elec-Mate

Written and reviewed by Andrew Moore, founder of Elec-Mate, against BS 7671:2018+A4:2026, IET Guidance Note 3 and the IET On-Site Guide.

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Key Takeaways

1Hard-wired garden lighting circuits in domestic premises must be protected by a 30mA RCD under BS 7671 Regulation 411.3.4 (A4:2026), which requires additional RCD protection for all AC final circuits supplying luminaires in domestic properties. Regulation 411.3.3 separately mandates 30mA RCD protection for socket-outlets rated up to 32A. If your garden lights are on a circuit without RCD protection, this is a C2 (potentially dangerous) finding that must be rectified.
2Garden lighting cables buried underground must comply with BS 7671 wiring regulations — either armoured cable (SWA) or cables in protective conduit at sufficient depth, with cable protection warning tape above.
3IP (Ingress Protection) ratings indicate how well a light fitting is protected against water and dust. Garden luminaires should be rated at minimum IP44 (splash-proof); fittings exposed to heavy rain or immersion require IP65 or higher.
4Low-voltage garden lighting systems (typically 12V) use a transformer to step down the mains voltage. Transformer failure is a common and easily replaced fault — most low-voltage garden lighting sets use plug-in or hard-wired transformers costing £20 to £80.
5Any new outdoor lighting circuit or significant modification in England and Wales is notifiable work under Part P of the Building Regulations, requiring either competent person scheme self-certification or local authority building control inspection.

01 · Fault Finding Guide

Outdoor Electrical Safety — The Key Risks

Outdoor electrical installations face hazards that do not exist indoors: rain, condensation, UV degradation, ground movement, mechanical damage from gardening tools, and contact with vegetation. These factors make outdoor electrical faults more common and more dangerous than equivalent indoor faults.

Outdoor electrical faults can be fatal

Water dramatically reduces the resistance of the human body. Contact with a live conductor in a wet outdoor environment — even at garden lighting voltages when mains-powered — can cause cardiac arrest. Never investigate an outdoor electrical fault without first switching off and proving dead at the consumer unit.

Safe isolation first — switch off the outdoor lighting circuit MCB at the consumer unit. If there is a dedicated outdoor circuit, this will be labelled. If not, switch off the ring main or radial that feeds the outdoor socket or junction box. Prove dead at the garden light supply point with a GS38-compliant voltage indicator before touching any connections.
Never assume plug-in is safe — garden lights connected via a plug to an outdoor socket are still live at mains voltage (230V) to the point of the transformer. Always unplug before investigating connections or luminaire faults.
Low-voltage systems still require care — 12V garden lighting systems are safer than mains voltage, but the transformer primary side is still mains voltage (230V). The secondary (12V) side is safe to touch but the transformer connections must not be accessed without isolating the primary supply first.

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02 · Fault Finding Guide

RCD Protection Requirements for Outdoor Circuits

Residual Current Device (RCD) protection is mandatory for all outdoor circuits under BS 7671:2018+A4:2026 (the 18th Edition Wiring Regulations). This requirement exists because outdoor environments dramatically increase the risk of electric shock.

Regulation 411.3.4 (A4:2026) — within domestic premises, requires additional protection by an RCD with a rated residual operating current (IΔn) not exceeding 30mA for all AC final circuits supplying luminaires. This is the primary regulation requiring 30mA RCD protection on hard-wired garden lighting circuits in domestic properties.
Regulation 411.3.3 — requires 30mA RCD protection for all socket-outlets with a rated current not exceeding 32A (with limited exceptions for non-dwellings only). This applies to outdoor socket circuits feeding plug-in garden lighting.
Where to fit the RCD — the RCD can be at the consumer unit (an RCD-protected circuit or RCBO), at an outdoor consumer unit or distribution board, or as an inline RCD socket. For plug-in garden lighting connected to an existing indoor socket, an RCD plug adapter (BS 1363 with 30mA RCD) provides protection at the point of use.
Missing RCD protection — if your outdoor lighting circuit was installed before RCD protection was mandatory (pre-2008 installations), it may lack RCD protection. This is a C2 (potentially dangerous) observation on an EICR and should be rectified by a qualified electrician.
RCD testing — outdoor RCDs should be tested monthly using the test button on the device. The test button verifies the mechanical trip mechanism: the RCD should trip promptly when the button is pressed with the circuit energised. If it does not trip at all, the device has failed and must be replaced immediately. The test button alone does not measure trip time or operating current; use a calibrated RCD tester for formal periodic verification.

03 · Fault Finding Guide

IP Ratings for Garden Lighting Explained

IP (Ingress Protection) ratings are defined in BS EN 60529 and indicate how well an electrical fitting is protected against solid particles (first digit) and water (second digit). Understanding IP ratings is essential for choosing and diagnosing outdoor lighting faults.

IP44 — protected against solid objects over 1mm and against splashing water from any direction. Suitable for covered porches and sheltered outdoor areas. Not suitable for exposed garden positions that receive direct rain.
IP54 / IP55 — dust-protected and splash-proof / water jet resistant. Suitable for most exposed garden locations including wall lights and post lights.
IP65 — fully dust-tight and protected against low-pressure water jets. The minimum recommended rating for exposed garden spotlights, path lights, and ground-spike fittings.
IP67 / IP68 — protected against temporary immersion (IP67) or continuous immersion (IP68). Required for pond lights, fountain lights, and in-ground fittings that may flood in heavy rain.

Using a fitting with a lower IP rating than required for its location is a common cause of garden lighting faults. Water ingress causes corrosion of terminals, short circuits, and degraded insulation — all of which can cause RCD tripping or complete failure. Always check the IP rating label on the fitting and match it to the installation environment.

04 · Fault Finding Guide

RCD Tripping on the Garden Lighting Circuit

An outdoor RCD that trips repeatedly has detected an earth leakage fault. The most common sources in garden lighting installations are:

Water-ingressed fitting — water inside the fitting creates a leakage path to earth. The RCD trips when the circuit is energised. Disconnect each fitting in turn, starting with any that appear wet or corroded, and reset the RCD between each disconnection. When the RCD holds after disconnecting a particular fitting, that fitting is the fault source.
Damaged underground cable — a nick, cut, or crush in the cable insulation allows moisture to penetrate and create an earth fault. The RCD trips reliably, regardless of which fitting is connected. Isolate all fittings and perform an insulation resistance test on the cable to identify a cable fault.
Failed transformer — if the transformer insulation has broken down, leakage current from the primary winding to the casing (earth) will trip the RCD. Disconnect the transformer and test it in isolation. If the RCD holds with the transformer disconnected, the transformer is the fault source.
Nuisance tripping from natural capacitance — long outdoor cable runs have significant capacitance to earth. In wet conditions, this capacitance can produce enough leakage current to trip a sensitive 10mA RCD. If you have a 10mA RCD on the garden circuit, consider upgrading to a 30mA RCD (which is the BS 7671 requirement anyway).

05 · Fault Finding Guide

Cable Damage in Garden Installations

Damaged or incorrectly installed cable is a primary cause of garden lighting faults. Underground cable is vulnerable to physical damage, and aerial cable is subject to UV degradation and mechanical damage.

Spade or fork damage — the most common cause of underground cable damage. A spade through a buried cable causes an immediate open circuit (lights go out) or a direct earth fault (RCD trips). If you suspect cable damage from gardening, mark the area and call an electrician — do not dig to investigate without first isolating the circuit.
Animal damage — rats, squirrels, and rabbits regularly chew through outdoor cable. Low-voltage garden lighting cable (typically 1.5mm² unarmoured) is particularly vulnerable. Armoured cable (SWA) or cable in conduit provides much better protection against animal damage.
UV degradation — standard PVC cable insulation degrades rapidly when exposed to direct sunlight. Cable run above ground or attached to fences must be rated for outdoor UV exposure (typically XLPE or LSF outdoor-grade cable) or protected in UV-resistant conduit.
Underburied cable — if cable was installed without being properly buried (or has been partially exposed by soil erosion), it is at immediate risk of damage. Cable must be reinstalled at the correct depth with armoured cable or in protective conduit with warning tape above.

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06 · Fault Finding Guide

Transformer Faults in Low-Voltage Garden Lighting

Low-voltage garden lighting systems (typically 12V DC or AC) use a transformer to convert the mains 230V supply to a safe low voltage. Transformer failure is common in cheaper systems and in systems that have been overloaded or exposed to water ingress.

Overloaded transformer — the transformer is rated for a maximum total wattage of connected lamps. Adding more lamps than the rated capacity causes the thermal protection to trip repeatedly or the transformer to fail permanently. Calculate the total wattage of all connected lamps and ensure it is below 80% of the transformer capacity.
Transformer not resetting — most transformers have internal thermal protection that cuts out when overloaded or overheated. Allow the transformer to cool for 30 minutes before testing. If it powers up after cooling but cuts out again under load, the transformer is overloaded or has a partially failed winding that runs hot.
Testing a plug-in transformer — plug the transformer into a known working indoor socket (not the outdoor socket, in case that is the fault). Measure the output voltage at the transformer terminals with a multimeter. A 12V transformer should read 11 to 14V AC (or DC depending on type) with no load connected. No output voltage confirms transformer failure.
Transformer replacement — plug-in garden lighting transformers cost £20 to £80 depending on capacity and quality. Hard-wired transformers require an electrician to disconnect and replace. Always match the replacement transformer to the voltage (12V AC or DC) and wattage requirements of the lighting system.

07 · Fault Finding Guide

Waterproofing Issues & Water Ingress

Water ingress into garden lighting fittings causes corrosion, short circuits, and earth faults. Even fittings with an appropriate IP rating can fail if seals deteriorate over time or if the fitting is incorrectly installed.

Failed gaskets and seals — the rubber gaskets that seal the lens or diffuser of a garden fitting degrade with UV exposure and thermal cycling. Inspect gaskets annually and replace when cracked, compressed, or no longer sealing correctly. Replacement gaskets are available from the fitting manufacturer or electrical wholesalers.
Cable entry points — cable glands must be correctly sized for the cable and tightened to form a watertight seal. Loose or incorrectly sized glands allow water to track along the cable into the fitting body. If a fitting is repeatedly ingressing water at the cable entry, re-gland or seal the entry with self-amalgamating tape.
Condensation inside the fitting — even IP65-rated fittings can develop condensation inside if there is a temperature differential between the inside and outside. A small silica gel desiccant bag placed inside the fitting during installation can help, but is not practical in all fitting types. Fittings that repeatedly develop condensation despite correct IP rating may need to be relocated to a less exposed position.

08 · Fault Finding Guide

Garden Lighting Repair Costs — 2026 Prices

The cost of repairing garden lighting depends heavily on whether the fault is in the luminaire, the transformer, or the underground cable. Here are typical UK costs for 2026:

Transformer replacement (plug-in) — £20 to £80 for the part. DIY replacement is possible for plug-in units. No electrician required.
Transformer replacement (hard-wired) — £80 to £200 all-in. Transformer £30 to £80, labour £50 to £120. A Minor Works Certificate must be issued.
Luminaire replacement — £20 to £150 per fitting depending on type and quality. Lamp replacements for LED fittings are typically £5 to £25 per lamp. Labour for fitting replacement is £30 to £60 per fitting.
Underground cable repair — £150 to £400 for a simple repair. Excavating to find and repair a cable fault, fitting an underground junction box, and reinstating the ground. Longer cable runs or deep excavation cost more.
RCD installation on existing circuit — £80 to £200. Adding RCD protection to an existing outdoor circuit, including an RCBO or RCD at the consumer unit. Notifiable work under Part P — a Minor Works Certificate must be issued.
New outdoor lighting circuit — £300 to £700 from consumer unit to garden positions. Includes armoured cable, consumer unit connection, RCD protection, and Electrical Installation Certificate.

09 · Fault Finding Guide

For Electricians: Garden Lighting Work

Garden lighting installation is notifiable work under Part P of the Building Regulations in England and Wales when it involves a new circuit or significant modification to an existing circuit. Work in a garden is included in the scope of Part P. Electricians registered with NICEIC, NAPIT, or ELECSA can self-certify outdoor electrical work and issue the relevant certificate on completion.

Key BS 7671 requirements to verify on any outdoor lighting installation:

30mA RCD additional protection on hard-wired luminaire circuits in domestic premises (Regulation 411.3.4, A4:2026) and on socket-outlet circuits rated up to 32A (Regulation 411.3.3)
Appropriate IP rating on all fittings for their installed location
Underground cable at sufficient depth to avoid foreseeable ground disturbance (Regulation 522.8.10) — SWA or cable in protective conduit, with cable route records provided to the customer
Section 714 (Outdoor Lighting Installations) compliance — A4:2026 revised Section 714 with updated automatic disconnection requirements and additional protection measures for outdoor lighting installations. Verify disconnection criteria against the amended Section 714 alongside Regulations 411.3.3 and 411.3.4
AFDD consideration (Regulation 421.1.7, A4:2026) — Regulation 421.1.7 recommends the installation of arc fault detection devices (AFDDs) in AC final circuits of a fixed installation to mitigate fire risk from arc fault currents. When installing a new hard-wired outdoor lighting circuit, assess whether an AFDD is appropriate

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Frequently Asked Questions — Garden Lighting Faults

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Garden Lighting Not Working: Outdoor Electrical Fault Finding

Key Takeaways

Outdoor Electrical Safety — The Key Risks

Get the BS 7671 A4:2026 Cheat Sheet — free

RCD Protection Requirements for Outdoor Circuits

IP Ratings for Garden Lighting Explained

RCD Tripping on the Garden Lighting Circuit

Cable Damage in Garden Installations

Try Elec-Mate free for 7 days

Transformer Faults in Low-Voltage Garden Lighting

Waterproofing Issues & Water Ingress

Garden Lighting Repair Costs — 2026 Prices

For Electricians: Garden Lighting Work

Issue Certificates On Site

Complete outdoor electrical certificates on your phone

Frequently Asked Questions — Garden Lighting Faults

Why have my garden lights stopped working?

Do garden lights need RCD protection?

What IP rating do garden lights need?

Can I install garden lights myself?

Why does my garden lighting transformer hum?

How deep do garden lighting cables need to be buried?

What should I do if a garden light fitting fills with water?

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