How to install outdoor festoon lights safely

Helpful video reference. The Screwfix channel video "How to install 4lite Festoon 20m Outdoor IP44" shows the full unboxing and installation of a typical IP44 festoon set. It covers connector assembly, bulb fitting and how the cable hangs correctly. Screwfix is one of the UK's largest trade and DIY retailers and their product demonstrations are practical and UK-specific.

1. Choose a safe supply point

The right supply for outdoor festoon lights is a permanently installed weatherproof socket mounted on the house wall or outbuilding, rated at least IP44. These are typically a double socket in a surface-mounted enclosure with a hinged or sprung cover over each outlet.

If there is no outdoor socket on the property, you have two options: have one installed (this is Part P notifiable work that requires an electrician), or use a purpose-made outdoor RCD extension lead rated for outdoor use and run it from the nearest indoor socket to a point just inside the door - not trailing through a gap.

Avoid using an indoor socket with a long extension lead routed outside. Standard indoor extension leads are not weatherproof and a coiled lead left outdoors becomes a fire risk.

2. Check the IP rating of the festoon set

Every festoon set sold for outdoor use should carry an IP rating on the packaging and ideally moulded into the connector bodies. IP44 means protection against solid particles greater than 1 mm and water splashing from any direction - adequate for temporary garden use. IP65 is better if the lights are to be left out all season.

Check the rating applies to the cable, the individual bulb holders and the end connector, not just the cable itself. On cheaper sets the connectors are often the weak point. If a bulb holder cracks or the connector does not seal properly, water ingress is possible even in a set sold as IP44.

3. Confirm RCD protection on the circuit

Under BS 7671 Regulation 411.3.3, all socket outlets outside the main equipotential bonding zone - which means every outdoor socket - must be protected by a 30 mA RCD. Most consumer units installed since 2008 include this. On older boards there may be no RCD protection at all on the outdoor circuit.

To check: plug something into the outdoor socket, then press the test button on the RCD in your consumer unit that covers that circuit. The circuit should go dead immediately. If nothing happens, or if you cannot identify which RCD covers the outdoor circuit, use an RCD adaptor in the socket and do not proceed without one.

If the board has no RCD at all on the outdoor circuit, this is a C2 fault under BS 7671 - call an electrician.

4. Plan the route and fix the support points

Walk the garden and work out where the cable will run. Festoon lights should hang in a relaxed catenary curve between support points - not pulled taut and not lying on the ground. The cable wants to be above head height in any area where people will walk underneath it.

Fix screw-in hooks, eye bolts or purpose-made festoon cable clips to fences, pergola uprights, house walls or posts before threading the cable. Space supports at no more than 1 to 1.5 metres to prevent the cable sagging down. On masonry walls, a hammer-drill pilot hole and a plastic plug takes a cup hook in about two minutes.

5. Thread the cable and fit the bulbs

Thread the festoon cable through the hooks first, letting it hang in the intended curve, before fitting any of the bulbs. On most 4lite-style sets the bulb holders have a bayonet or screw fitting - finger-tight is sufficient, do not overtighten or you may crack the polycarbonate housing.

Some sets have bulbs pre-fitted in the holders and separate screw-cap weatherproof covers. Fit the cover first, thread the cable, then screw the holder in. If the set has a single strand of five or more bulbs to a connector block, check whether the blocks daisy-chain correctly before hanging the full run.

6. Connect to the outdoor socket

Plug the festoon set directly into the outdoor socket. Do not use an indoor extension lead or a standard trailing socket outdoors. If the run is long and you need to extend it, use an outdoor-rated extension lead (IP44 minimum, clearly labelled for outdoor use) that is fully uncoiled and lying flat on a dry surface, not coiled or hanging in a loop.

Turn on the outdoor socket circuit at the consumer unit if it has its own switch, then switch on at the socket.

7. Test and inspect the full run

Walk the complete run and check every bulb holder is seated and every connector is clicked home. Look for any holders where water may collect. Press the test button on the RCD (or RCD adaptor) to confirm it trips cleanly and note the reset position.

Leave the lights on for ten to fifteen minutes and walk the run again to check for any fittings that are warm to the touch. LED festoon sets run cool at the holder but a failing bulb or a loose connection can generate heat. Any warmth beyond what you expect from a lit bulb is a reason to switch off and inspect.

A permanent outdoor socket makes everything easier

If you find yourself running cable through a window every summer, the right answer is a permanently installed IP66 double socket on the outside wall, fed from a dedicated spur on the house ring circuit. It is Part P work in England and must be done by an electrician, but it costs far less than you might expect and makes the garden usable year-round. Richard installs outdoor sockets in Sandwich and east Kent regularly - the job usually takes less than two hours.