Outdoor Christmas lights: ratings, power and safety
An outdoor set is three things: bulbs and cable sealed against rain, a transformer that drops the mains to a low voltage, and a maker’s rating that says it is for outside. Get those three right and the rest is clips and common sense.
IP ratings
The IP code on a set has two digits. The first is protection against solids, the second against water. For Christmas lights the second digit is the one that matters.
| Rating | Water protection | Use |
|---|---|---|
| IP20 | None | Indoors only |
| IP44 | Splashes from any direction | Minimum for outdoors; sheltered rooflines, porches, trees |
| IP65 | Water jets; dust tight | Exposed fences, gutters, open gardens |
The rating applies to the lights and cable, not to the transformer or the plug, which are rarely sealed. The weakest part of the installation sets its real rating: an IP65 set plugged into an indoor extension lead lying on the lawn is an indoor installation.
Low voltage
Nearly all the outdoor sets we sell run at 24V or 31V through a transformer that plugs into the mains. The cable in the garden carries that low voltage, so a nick in the insulation or water in a joint is a fault, not a danger. Mains-voltage sets, where 230V runs the whole length of the cable, are now rare for garden use and we do not recommend them where a low-voltage set will do.
Where the transformer goes
Indoors, with the lead run through a window or a door, is simplest. If the socket is outside, use an RCD-protected outdoor socket and put the transformer and plug in a weatherproof enclosure such as a Dri-Box, raised off the ground and with the cable glands facing down. Never leave a transformer on the soil or in a puddle, and never wrap one in a plastic bag, which traps condensation.
Marks to look for
UKCA or CE marking on the transformer and packaging; BS EN 60598-2-20, the standard for lighting chains; and an IP rating printed on the set. A proper moulded UK plug and the maker’s name and address on the box are the signs of a set that has been through conformity testing. All the sets here are from established UK suppliers (Premier, Festive, Snow Time, Noma, Lumineo) and carry the marks.
Fixing without damage
Use gutter clips, suction hooks and cable clips, spaced every 30 to 50cm, rather than nails or staples, which pierce the insulation. Keep connectors off the ground and pointing down so water drains away. Stake lights push fully into soil; weight or plant them on hard surfaces. Check the set after a storm.
Running cost
LED sets draw very little. A 500 LED set is typically around 15W, which at the current price cap of about 26p per kWh costs roughly 0.4p an hour, or 2.4p for a six-hour evening on the timer. A whole house front of 3,000 LEDs is still under 15p a night. The wattage is on the transformer label.
Common questions
Can I use indoor lights outside if it is dry?
No. Dew, frost and condensation reach an indoor set even without rain, and the transformer is not rated for cold damp air. Use only sets rated outdoor or indoor and outdoor.
Does the transformer need to be IP rated?
It needs to be kept dry. Most are not sealed, which is why they belong indoors or in a weatherproof enclosure off the ground.
Do I need an outdoor socket?
Not necessarily. Running the lead through a window to an indoor socket is the simplest safe arrangement. If you use an outdoor socket, it should have RCD protection.