These common eBay strings of lights are delightfully trashy. They seem a complete bargain at just £3.50 shipped (twice that or more at Christmas time). But the low price comes at the cost of safety. They are made down to a price, and that means they run directly at mains voltage with the incoming supply being converted from AC to DC and then used to run long strings of LEDs in series with a smattering of undersized resistors soldered to the first few LEDs.
In some instances these LED strings do have applications, but only indoors out of reach of humans and pets. And only used in static mode if the resistors in the first few LEDs of the string don't rapidly start going brown!
If used outdoors around handrails or foliage there is a risk of current flow if water wicks into the LED sleeves and bridges to conductive material. Worse still, that current leakage will be DC, which can defeat some older RCDs/GFCIs and even desensitise them to other leakage faults elsewhere.
The fake 13A plug to make them look UK compliant is just scraping the barrel. Especially the matching fake fuse that isn't even connected in circuit.
If you want safe Christmas lights then choose the ones with the plug in low-voltage power supplies. Kids and pets are attracted to strings of fairy lights, so it makes sense to pay a bit extra for safe ones that won't give an electric shock when played with or chewed.
The really annoying thing is that these strings of lights are so close to being safer. Better wire, double sleeving, more resistors and preferably just a rectifier and no flashing patterns to get rid of that nasty control box. It could make for quite useable lights.
Note that any heat shrink sleeved LED lighting strings will wick in water and corrode when used outdoors. If you have a project you want to last more than one or two seasons in a wet environment, then choose the much more expensive rubber cable municipal lights with the LEDs and their resistors potted individually in resin filled caps.
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